Short blog post today. These are a couple of generic serialize and deserialize methods that can be easily used when needing to serialize and deserialize classes. The methods work with any .Net type. That includes built-in .Net types and custom classes that you might create yourself. These methods will only serialize PUBLIC properties of a class. Also, the XML will be human-readable instead of one long line of text. Serialize Method /// /// Serializes the data in the object to the designated file path /// /// Type of Object to serialize /// Object to serialize /// FilePath for the XML file public static void Serialize(T dataToSerialize, string filePath) { try { using (Stream stream = File.Open(filePath, FileMode.Create, FileAccess.ReadWrite)) { XmlSerializer serializer = new XmlSerializer(typeof(T)); XmlTextWriter writer = new XmlTextWriter(stream, Encoding.Default); writer.Formatting = Formatting.Indented; serializer.Serialize(writer, dataToSerialize); writer.Close(); } } catch { throw; } } Deserialize Method /// /// Deserializes the data in the XML file into an object /// /// Type of object to deserialize /// FilePath to XML file /// Object containing deserialized data public static T Deserialize(string filePath) { try { XmlSerializer serializer = new XmlSerializer(typeof(T)); T serializedData; using (Stream stream = File.Open(filePath, FileMode.Open, FileAccess.Read)) { serializedData = (T)serializer.Deserialize(stream); } return serializedData; } catch { throw; } } Here is some sample code to show the methods in action. Person p = new Person() { Name = "John Doe", Age = 42 }; XmlHelper.Serialize(p, @"D:\text.xml"); Person p2 = new Person(); p2 = XmlHelper.Deserialize(@"D:\text.xml"); Console.WriteLine("Name: {0}", p2.Name); Console.WriteLine("Age: {0}", p2.Age); Console.Read();

Check out an example of the volatile Java keyword.

CSS3 Fade slider Today I would like to show you how to create nice and smooth css3 slider. It uses fade effect to switch between slides. Plus, you can use custom promo text for each slide. We will use basic UL-LI unordered list to make this slider. We don’t need to click anywhere to switch slides – everything is automatically (css3 animation). Live Demo download result So, lets start Step 1. HTML Html markup is very easy. There are four slides. Each slide consists of image (as background) and promo text in DIV. If you need – you always can add more slides here. Promo text #1 Promo text #2 Promo text #3 Promo text #4 Step 2. CSS Now, it’s time to define css styles for our slider. Here are styles for main slider element, inner slides and for promo titles: /* fade slider */ .slides { height:300px; margin:50px auto; overflow:hidden; position:relative; width:900px; } .slides ul { list-style:none; position:relative; } /* keyframes #anim_slides */ @-webkit-keyframes anim_slides { 0% { opacity:0; } 6% { opacity:1; } 24% { opacity:1; } 30% { opacity:0; } 100% { opacity:0; } } @-moz-keyframes anim_slides { 0% { opacity:0; } 6% { opacity:1; } 24% { opacity:1; } 30% { opacity:0; } 100% { opacity:0; } } .slides ul li { opacity:0; position:absolute; top:0; /* css3 animation */ -webkit-animation-name: anim_slides; -webkit-animation-duration: 24.0s; -webkit-animation-timing-function: linear; -webkit-animation-iteration-count: infinite; -webkit-animation-direction: normal; -webkit-animation-delay: 0; -webkit-animation-play-state: running; -webkit-animation-fill-mode: forwards; -moz-animation-name: anim_slides; -moz-animation-duration: 24.0s; -moz-animation-timing-function: linear; -moz-animation-iteration-count: infinite; -moz-animation-direction: normal; -moz-animation-delay: 0; -moz-animation-play-state: running; -moz-animation-fill-mode: forwards; } /* css3 delays */ .slides ul li:nth-child(2), .slides ul li:nth-child(2) div { -webkit-animation-delay: 6.0s; -moz-animation-delay: 6.0s; } .slides ul li:nth-child(3), .slides ul li:nth-child(3) div { -webkit-animation-delay: 12.0s; -moz-animation-delay: 12.0s; } .slides ul li:nth-child(4), .slides ul li:nth-child(4) div { -webkit-animation-delay: 18.0s; -moz-animation-delay: 18.0s; } .slides ul li img { display:block; } /* keyframes #anim_titles */ @-webkit-keyframes anim_titles { 0% { left:100%; opacity:0; } 5% { left:10%; opacity:1; } 20% { left:10%; opacity:1; } 25% { left:100%; opacity:0; } 100% { left:100%; opacity:0; } } @-moz-keyframes anim_titles { 0% { left:100%; opacity:0; } 5% { left:10%; opacity:1; } 20% { left:10%; opacity:1; } 25% { left:100%; opacity:0; } 100% { left:100%; opacity:0; } } .slides ul li div { background-color:#000000; border-radius:10px 10px 10px 10px; box-shadow:0 0 5px #FFFFFF inset; color:#FFFFFF; font-size:26px; left:10%; margin:0 auto; padding:20px; position:absolute; top:50%; width:200px; /* css3 animation */ -webkit-animation-name: anim_titles; -webkit-animation-duration: 24.0s; -webkit-animation-timing-function: linear; -webkit-animation-iteration-count: infinite; -webkit-animation-direction: normal; -webkit-animation-delay: 0; -webkit-animation-play-state: running; -webkit-animation-fill-mode: forwards; -moz-animation-name: anim_titles; -moz-animation-duration: 24.0s; -moz-animation-timing-function: linear; -moz-animation-iteration-count: infinite; -moz-animation-direction: normal; -moz-animation-delay: 0; -moz-animation-play-state: running; -moz-animation-fill-mode: forwards; } You can see that I use two css3 animations here: anim_slides and anim_titles. First one is for separated slides, second one – for promo texts. In order to switch between slides – we change opacity of slides. For titles – we change Left position and opacity too. Live Demo download result Conclusion That is all for today. We have just created new cool pure CSS3-based slider with Fade effect. I hope that you like it. Good luck!

from timeit import default_timer class Timer(object): def __init__(self, verbose=False): self.verbose = verbose self.timer = default_timer def __enter__(self): self.start = self.timer() return self def __exit__(self, *args): end = self.timer() self.elapsed_secs = end - self.start self.elapsed = self.elapsed_secs * 1000 # millisecs if self.verbose: print 'elapsed time: %f ms' % self.elapsed To use the Timer (context manager object), invoke it using Python's `with` statement. The duration of the context (code inside your `with` block) will be timed. It uses the appropriate timer for your platform, via the `timeit` module. Timer is used like this: with Timer() as target: # block of code goes here. # result (elapsed time) is stored in `target` properties. Example script: timing a web request (HTTP GET), using the `requests` module. #!/usr/bin/env python import requests from timer import Timer url = 'https://github.com/timeline.json' with Timer() as t: r = requests.get(url) print 'fetched %r in %.2f millisecs' % (url, t.elapsed) Output: fetched 'https://github.com/timeline.json' in 458.76 millisecs `timer.py` in GitHub Gist form, with more examples: #!/usr/bin/env python # # Python Timer Class - Context Manager for Timing Code Blocks # Corey Goldberg - 2012 # from timeit import default_timer class Timer(object): def __init__(self, verbose=False): self.verbose = verbose self.timer = default_timer def __enter__(self): self.start = self.timer() return self def __exit__(self, *args): end = self.timer() self.elapsed_secs = end - self.start self.elapsed = self.elapsed_secs * 1000 # millisecs if self.verbose: print 'elapsed time: %f ms' % self.elapsed if __name__ == '__main__': # example: # 'HTTP GET' from requests module, inside timer blocks. # invoke the Timer context manager using the `with` statement. import requests url = 'https://github.com/timeline.json' # verbose (auto) timer output with Timer(verbose=True): r = requests.get(url) # print stored elapsed time in milliseconds with Timer() as t: r = requests.get(url) print 'response time (millisecs): %.2f' % t.elapsed # print stored elapsed time in seconds with Timer() as t: r = requests.get(url) print 'response time (secs): %.3f' % t.elapsed_secs # example output: # # $ python timer.py # elapsed time: 652.403831 ms # response time (millisecs): 635.49 # response time (secs): 0.624

Performance problems are one of the biggest challenges to expect when designing and implementing Java EE related technologies.

There are several cool ways to create PDFs with Python. In this article we will be focusing on a cool little tool called rst2pdf, which takes a text file that contains Restructured Text and converts it to a PDF. The rst2pdf package requires Reportlab to function. This won’t be a tutorial on Restructured Text, although we’ll have to discuss it to some degree just to understand what’s going on. Getting Started First off we’ll need to create a document with the required markup. Let’s do that first. Here’s some simple restructured text with a couple of directives mixed in. We’ll explain everything after you’ve had a chance to read the code: .. header:: Python Rules! - page ###Page### ===== Title ===== This is some blah blah blah .. raw:: pdf PageBreak oneColumn New section =========== yada yada yada import urllib import urllib2 import webbrowser url = "http://duckduckgo.com/html" data = urllib.urlencode({'q': 'Python'}) results = urllib2.urlopen(url, data) with open("results.html", "w") as f: f.write(results.read()) webbrowser.open("results.html") The first couple lines define the header that will be on every page. In this case, we’re going to have “Python Rules!” printed at the top of every page along with a page number. There are several other special hash-mark insert directives available. You should check out the official documentation for more information on those. Then we have a Title. Note that it is preceded and followed by a bunch of equal signs that are the same length as the text. This tells us that this text will be styled and centered. The following line is just a lame sentence for demonstration purposes. Next up is another special directive which tells rst2pdf to insert a page break. The second page contains a section header, a lame sentence and a code example that’s color-coded. To generate the PDF, you’ll need to do something like this on the command line: rst2pdf test.rst -o out.pdf You can also run rst2pdf against a config file to control some of the special PDF directives, like header and footer, etc. The information about how to make the config file get read is a little confusing though. It sounds like you have to place the file in a specific location: /etc/rst2pdf.conf and ~/.rst2pdf/config. There’s also a –config flag you can pass, but I’ve found various reports online that that doesn’t work, so your mileage may vary. There’s a sample config file in the project’s repo that you’ll find instructive. Wrapping Up I was hoping that rst2pdf would allow an easy way to specify absolute positions and create lines and boxes so I could replace an XSL / XML project I was working on with something much more simple. Alas, rst2pdf just doesn’t support the lines and boxes that reportlab itself does at the time of this writing. However if you need something easy to use to create your documents with and you already know restructured text, I think this is a very good way to go. You can also take your restructured text skills and use them with the Sphinx documentation project.

Apache Camel has a very powerful bean injection framework which allows developers to focus only on solving business problems. However there are situations when you need to do a little bit more. Read below to see how easy it is to setup aspects (AspectJ) in Apache Camel. Use case In Qualitas I have an installation route which consists of 10 mandatory and 2 optional processors. Some processors like property resolvers or validators don't modify contents of message's body so I have to always copy body from the in message to out message. Also, all my processors require some headers to function properly. Finally, I would like to get a status updated after each of my processors either finishes processing successfully or fails. Setting up AspectJ This is just a plain Spring configuration frankly. All you have to do is: Apache Camel processor aspect To define aspect in AspectJ I used AspectJ-specific @Aspect and @Around annotations: @Aspect @Component @Order(Ordered.LOWEST) public class HeadersAndBodyCopierAspect { @Around("execution(* com.googlecode.qualitas.internal.installation..*.process(org.apache.camel.Exchange)) && args(exchange) && target(org.apache.camel.Processor)") public Object copyHeadersAndBody(ProceedingJoinPoint pjp, Exchange exchange) throws Throwable { Object retValue = pjp.proceed(); Message in = exchange.getIn(); Message out = exchange.getOut(); // always copy headers out.setHeaders(in.getHeaders()); // if output body is empty copy it from input if (out.getBody() == null) { out.setBody(in.getBody()); } return retValue; } } I also used @Order Spring-specific annotation to control the order of execution of my aspects and @Component for automatic context scanning. Now, the join point is defined as execution(* com.googlecode.qualitas.internal.installation..*.process(org.apache.camel.Exchange)) && args(exchange) && target(org.apache.camel.Processor) which basically means: apply this aspect to all process methods which are defined in all classes in com.googlecode.qualitas.internal.installation or subpackages and which take Exchange object as an argument there can be many custom methods whose names may be process and whose argument may be Exchange, so I added one more constraint, this class has to be an instance of Processor args(exchange) allows me to add Exchange object as an argument to my aspect More complex aspects and source code Of course in Spring you can inject other beans directly into your aspects. I used it in my ProcessStatusUpdaterAspect aspect which you can find in Qualitas repo on GoogleCode or GitHub. If you are interested in trying out the whole Qualitas system take a look at the following two links: BuildingTheProject and RunningTheProject. cheers, Łukasz

This article is part 2 of our NoClassDefFoundError troubleshooting series. It will focus and describe the simplest type of NoClassDefFoundError problem. This article is ideal for Java beginners and I highly recommend that you compile and run the sample Java program yourself. The following writing format will be used going forward and will provide you with: - Description of the problem case and type of NoClassDefFoundError - Sample Java program “simulating” the problem case - ClassLoader chain view - Recommendations and resolution strategies NoClassDefFoundError problem case 1 – missing JAR file The first problem case we will cover is related to a Java program packaging and / or classpath problem. A typical Java program can include one or many JAR files created at compile time. NoClassDefFoundError can often be observed when you forget to add JAR file(s) containing Java classes referenced by your Java or Java EE application. This type of problem is normally not hard to resolve once you analyze the Java Exception and missing Java class name. Sample Java program The following simple Java program is split as per below: - The main Java program NoClassDefFoundErrorSimulator - The caller Java class CallerClassA - The referencing Java class ReferencingClassA - A util class for ClassLoader and logging related facilities JavaEETrainingUtil This program is simple attempting to create a new instance and execute a method of the Java class CallerClassA which is referencing the class ReferencingClassA.It will demonstrate how a simple classpath problem can trigger NoClassDefFoundError. The program is also displaying detail on the current class loader chain at class loading time in order to help you keep track of this process. This will be especially useful for future and more complex problem cases when dealing with larger class loader chains. #### NoClassDefFoundErrorSimulator.java package org.ph.javaee.training1; import org.ph.javaee.training.util.JavaEETrainingUtil; /** * NoClassDefFoundErrorTraining1 * @author Pierre-Hugues Charbonneau * */ public class NoClassDefFoundErrorSimulator { /** * @param args */ public static void main(String[] args) { System.out.println("java.lang.NoClassDefFoundError Simulator - Training 1"); System.out.println("Author: Pierre-Hugues Charbonneau"); System.out.println("http://javaeesupportpatterns.blogspot.com"); // Print current Classloader context System.out.println("\nCurrent ClassLoader chain: "+JavaEETrainingUtil.getCurrentClassloaderDetail()); // 1. Create a new instance of CallerClassA CallerClassA caller = new CallerClassA(); // 2. Execute method of the caller caller.doSomething(); System.out.println("done!"); } } #### CallerClassA.java package org.ph.javaee.training1; import org.ph.javaee.training.util.JavaEETrainingUtil; /** * CallerClassA * @author Pierre-Hugues Charbonneau * */ public class CallerClassA { private final static String CLAZZ = CallerClassA.class.getName(); static { System.out.println("Classloading of "+CLAZZ+" in progress..."+JavaEETrainingUtil.getCurrentClassloaderDetail()); } public CallerClassA() { System.out.println("Creating a new instance of "+CallerClassA.class.getName()+"..."); } public void doSomething() { // Create a new instance of ReferencingClassA ReferencingClassA referencingClass = new ReferencingClassA(); } } #### ReferencingClassA.java package org.ph.javaee.training1; import org.ph.javaee.training.util.JavaEETrainingUtil; /** * ReferencingClassA * @author Pierre-Hugues Charbonneau * */ public class ReferencingClassA { private final static String CLAZZ = ReferencingClassA.class.getName(); static { System.out.println("Classloading of "+CLAZZ+" in progress..."+JavaEETrainingUtil.getCurrentClassloaderDetail()); } public ReferencingClassA() { System.out.println("Creating a new instance of "+ReferencingClassA.class.getName()+"..."); } public void doSomething() { //nothing to do... } } #### JavaEETrainingUtil.java package org.ph.javaee.training.util; import java.util.Stack; import java.lang.ClassLoader; /** * JavaEETrainingUtil * @author Pierre-Hugues Charbonneau * */ public class JavaEETrainingUtil { /** * getCurrentClassloaderDetail * @return */ public static String getCurrentClassloaderDetail() { StringBuffer classLoaderDetail = new StringBuffer(); Stack classLoaderStack = new Stack(); ClassLoader currentClassLoader = Thread.currentThread().getContextClassLoader(); classLoaderDetail.append("\n-----------------------------------------------------------------\n"); // Build a Stack of the current ClassLoader chain while (currentClassLoader != null) { classLoaderStack.push(currentClassLoader); currentClassLoader = currentClassLoader.getParent(); } // Print ClassLoader parent chain while(classLoaderStack.size() > 0) { ClassLoader classLoader = classLoaderStack.pop(); // Print current classLoaderDetail.append(classLoader); if (classLoaderStack.size() > 0) { classLoaderDetail.append("\n--- delegation ---\n"); } else { classLoaderDetail.append(" **Current ClassLoader**"); } } classLoaderDetail.append("\n-----------------------------------------------------------------\n"); return classLoaderDetail.toString(); } } Problem reproduction In order to replicate the problem, we will simply “voluntary” omit one of the JAR files from the classpath that contains the referencing Java class ReferencingClassA. The Java program is packaged as per below: - MainProgram.jar (contains NoClassDefFoundErrorSimulator.class and JavaEETrainingUtil.class) - CallerClassA.jar (contains CallerClassA.class) - ReferencingClassA.jar (contains ReferencingClassA.class) Now, let’s run the program as is: ## Baseline (normal execution) .\bin>java -classpath CallerClassA.jar;ReferencingClassA.jar;MainProgram.jar org.ph.javaee.training1.NoClassDefFoundErrorSimulator java.lang.NoClassDefFoundError Simulator - Training 1 Author: Pierre-Hugues Charbonneau http://javaeesupportpatterns.blogspot.com Current ClassLoader chain: ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Classloading of org.ph.javaee.training1.CallerClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Creating a new instance of org.ph.javaee.training1.CallerClassA... Classloading of org.ph.javaee.training1.ReferencingClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Creating a new instance of org.ph.javaee.training1.ReferencingClassA... done! For the initial run (baseline), the main program was able to create a new instance of CallerClassA and execute its method successfully; including successful class loading of the referencing class ReferencingClassA. ## Problem reproduction run (with removal of ReferencingClassA.jar) ../bin>java -classpath CallerClassA.jar;MainProgram.jar org.ph.javaee.training1.NoClassDefFoundErrorSimulator java.lang.NoClassDefFoundError Simulator - Training 1 Author: Pierre-Hugues Charbonneau http://javaeesupportpatterns.blogspot.com Current ClassLoader chain: ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Classloading of org.ph.javaee.training1.CallerClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- Creating a new instance of org.ph.javaee.training1.CallerClassA... Exception in thread "main" java.lang.NoClassDefFoundError: org/ph/javaee/training1/ReferencingClassA at org.ph.javaee.training1.CallerClassA.doSomething(CallerClassA.java:25) at org.ph.javaee.training1.NoClassDefFoundErrorSimulator.main(NoClassDefFoundErrorSimulator.java:28) Caused by: java.lang.ClassNotFoundException: org.ph.javaee.training1.ReferencingClassA at java.net.URLClassLoader$1.run(Unknown Source) at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 2 more What happened? The removal of the ReferencingClassA.jar, containing ReferencingClassA, did prevent the current class loader to locate this referencing Java class at runtime leading to ClassNotFoundException and NoClassDefFoundError. This is the typical Exception that you will get if you omit JAR file(s) from your Java start-up classpath or within an EAR / WAR for Java EE related applications. ClassLoader view Now let’s review the ClassLoader chain so you can properly understand this problem case. As you saw from the Java program output logging, the following Java ClassLoaders were found: Classloading of org.ph.javaee.training1.CallerClassA in progress... ----------------------------------------------------------------- sun.misc.Launcher$ExtClassLoader@17c1e333 --- delegation --- sun.misc.Launcher$AppClassLoader@214c4ac9 **Current ClassLoader** ----------------------------------------------------------------- ** Please note that the Java bootstrap class loader is responsible to load the core JDK classes and is written in native code ** ## sun.misc.Launcher$AppClassLoader This is the system class loader responsible to load our application code found from the Java classpath specified at start-up. ##sun.misc.Launcher$ExtClassLoader This is the extension class loader responsible to load code in the extensions directories (/lib/ext, or any other directory specified by the java.ext.dirs system property). As you can see from the Java program logging output, the extension class loader is the actual super parent of the system class loader. Our sample Java program was loaded at the system class loader level. Please note that this class loader chain is very simple for this problem case since we did not create child class loaders at this point. This will be covered in future articles. Recommendations and resolution strategies Now find below my recommendations and resolution strategies for NoClassDefFoundError problem case 1: - Review the java.lang.NoClassDefFoundError error and identify the missing Java class - Verify and locate the missing Java class from your compile / build environment - Determine if the missing Java class is from your application code, third part API or even the Java EE container itself. Verify where the missing JAR file(s) is / are expected to be found - Once found, verify your runtime environment Java classpath for any typo or missing JAR file(s) - If the problem is triggered from a Java EE application, perform the same above steps but verify the packaging of your EAR / WAR file for missing JAR and other library file dependencies such as MANIFEST Please feel free to post any question or comment. The part 3 will be available shortly.

There are several code analysis tools for Python. The most well known is pylint. Then there’s pychecker and now we’re moving on to pyflakes. The pyflakes project is a part of something known as the Divmod Project. Pyflakes doesn’t actually execute the code it checks, unlike pychecker. Of course, pylint also doesn’t execute the code. Regardless, we’ll take a quick look at it and see how pyflakes works and if it’s better than the competition. Getting Started As you have probably guessed, pyflakes is not a part of the Python distribution. You will need to download it from PyPI or from the project’s launchpad page. Once you have it installed, you can run it against some of your own code. Or you can follow along and see how it works with our test script. Running pyflakes We’ll be using a super simple and pretty silly example script. In fact, it’s the same one we used for the pylint and pychecker articles. Here it is again for your viewing pleasure: import sys ######################################################################## class CarClass: """""" #---------------------------------------------------------------------- def __init__(self, color, make, model, year): """Constructor""" self.color = color self.make = make self.model = model self.year = year if "Windows" in platform.platform(): print "You're using Windows!" self.weight = self.getWeight(1, 2, 3) #---------------------------------------------------------------------- def getWeight(this): """""" return "2000 lbs" As was noted in the other articles, this dumb code has 4 issues, 3 of which would stop the programming from running. Let’s see what pyflakes can find! Try running the following command and you’ll see the following output: C:\Users\mdriscoll\Desktop>pyflakes crummy_code.py crummy_code.py:1: 'sys' imported but unused crummy_code.py:15: undefined name 'platform' While pyflakes was super fast at returning this output, it didn’t find all the errors. The getWeight method call is passing too many arguments and getWeight method itself is defined incorrectly as it doesn’t have a “self” argument. If you fixed your code according to what pyflakes told you, you’re code still wouldn’t work. Wrapping Up The pyflakes website claims that pyflakes is faster than pychecker and pylint. I didn’t test this, but anyone who wants to can do so pretty easily by just running it against some big files. Maybe grab the BeautifulSoup file or run it (and the others) against something complex like PySide or SQLAlchemy and see how they compare. I personally am disappointed that it didn’t catch all the issues I was looking for. I think for my purposes, I’ll be sticking with pylint. This might be a handy tool for a quick and dirty test or just to make you feel better after a particularly poor result from a pylint scan.

Let’s assume that you’re writing code that’d track the price of mobile phones. Now, let’s say you have a collection of objects representing different Mobile phone vendors (MobileVendor), and each vendor has a collection of objects representing the PhoneModels they offer. To put it simple, there’s exists a one-to-many relationship between MobileVendor:PhoneModel. MobileVendor Class Class MobileVendor{ long vendor_id; PhoneModel[] phoneModels; ... } Okay, so you want to print out all the details of phone models. A naive O/R implementation would SELECT all mobile vendors and then do N additional SELECTs for getting the information of PhoneModel for each vendor. -- Get all Mobile Vendors SELECT * FROM MobileVendor; -- For each MobileVendor, get PhoneModel details SELECT * FROM PhoneModel WHERE MobileVendor.vendorId=? As you see, the N+1 problem can happen if the first query populates the primary object and the second query populates all the child objects for each of the unique primary objects returned. Resolve N+1 SELECTs problem (i) HQL fetch join "from MobileVendor mobileVendor join fetch mobileVendor.phoneModel PhoneModels" Corresponding SQL would be (assuming tables as follows: t_mobile_vendor for MobileVendor and t_phone_model for PhoneModel) SELECT * FROM t_mobile_vendor vendor LEFT OUTER JOIN t_phone_model model ON model.vendor_id=vendor.vendor_id (ii) Criteria query Criteria criteria = session.createCriteria(MobileVendor.class); criteria.setFetchMode("phoneModels", FetchMode.EAGER); In both cases, our query returns a list of MobileVendor objects with the phoneModels initialized. Only one query needs to be run to return all the PhoneModel and MobileVendor information required.

Today we’ll spend some time looking at three different ways to make Python submit a web form. In this case, we will be doing a web search with duckduckgo.com searching on the term “python” and saving the result as an HTML file. We will use Python’s included urllib modules and two 3rd party packages: requests and mechanize. We have three small scripts to cover, so let’s get cracking! Submitting a web form with urllib We will start with urllib and urllib2 since they are included in Python’s standard library. We’ll also import the webbrowser to open the search results for viewing. Here’s the code: import urllib import urllib2 import webbrowser url = "http://duckduckgo.com/html" data = urllib.urlencode({'q': 'Python'}) results = urllib2.urlopen(url, data) with open("results.html", "w") as f: f.write(results.read()) webbrowser.open("results.html") The first thing you have to do when you want to submit a web form is figure out what the form is called and what the url is that you will be posting to. If you go to duckduckgo’s website and view the source, you’ll notice that its action is pointing to a relative link, “/html”. So our url is “http://duckduckgo.com/html”. The input field is named “q”, so to pass duckduckgo a search term, we have to pass it to the “q” field. This is where the urllib.urlencode line comes in. It encodes our search term correctly and then we open the url and search. The results are read and written to disk. Finally, we open our saved results using the webbrowser module. Now let’s find out how this process differs when using the requests package. Submitting a web form with requests The requests package does form submissions a little bit more elegantly. Let’s take a look: import requests url = "http://duckduckgo.com/html" payload = {'q':'python'} r = requests.post(url, payload) with open("requests_results.html", "w") as f: f.write(r.content) With requests, you just need to create a dictionary with the field name as the key and the search term as the value. Then you use requests.post to do the search. Finally you use the resulting requests object, “r”, and access its content property which you save to disk. We skipped the webbrowser part in this example (and the next) for brevity. Now we should be ready to see how mechanize does its thing. Submitting a web form with mechanize The mechanize module has lots of fun features for browsing the internet with Python. Sadly it doesn’t support javascript. Anyway, let’s get on with the show! import mechanize url = "http://duckduckgo.com/html" br = mechanize.Browser() br.set_handle_robots(False) # ignore robots br.open(url) br.select_form(name="x") br["q"] = "python" res = br.submit() content = res.read() with open("mechanize_results.html", "w") as f: f.write(content) As you can see, mechanize is a little more verbose than the other two methods were. We also need to tell it to ignore the robots.txt directive or it will fail. Of course, if you want to be a good netizen, then you shouldn’t ignore it. Anyway, to start off, you need a Browser object. Then you open the url, select the form (in this case, “x”) and set up a dictionary with the search parameters as before. Note that in each method, the dict setup is a little different. Next you submit the query and read the result. Finally you save the result to disk and you’re done! Wrapping Up Of the three, requests was probably the simplest with urllib being a close second. Mechanize is made for doing a lot more then the other two though. It’s made for screen scraping and website testing, so it’s no surprise it’s a little more verbose. You can also do form submission with selenium, but you can read about that in this blog’s archives. I hope you found this article interesting and perhaps inspiring. See you next time!

A couple years ago I started a series of articles on XML parsing. I covered lxml’s etree and Python builtin minidom XML parsing library. For whatever reason I didn’t notice lxml’s objectify sub-package, but I saw it recently and decided to check it out. In my mind, the objectify module seems to be even more “Pythonic” than etree is. Let’s take some time and go over my old XML examples using objectify and see how it’s different! Let’s Get This Party Started! If you haven’t already, go out and download lxml or you won’t be able to follow along very well. Once you have it, we can continue. We’ll be using the following piece of XML for our parsing pleasure: 1181251680 040000008200E000 1181572063 1800 Bring pizza home 1234360800 1800 Check MS Office website for updates 604f4792-eb89-478b-a14f-dd34d3cc6c21-1234360800 dismissed Now we need to write some code that can parse and modify the XML. Let’s take a look at this little demo that shows a bunch of the neat abilities that objectify provides. from lxml import etree, objectify #---------------------------------------------------------------------- def parseXML(xmlFile): """""" with open(xmlFile) as f: xml = f.read() root = objectify.fromstring(xml) # returns attributes in element node as dict attrib = root.attrib # how to extract element data begin = root.appointment.begin uid = root.appointment.uid # loop over elements and print their tags and text for e in root.appointment.iterchildren(): print "%s => %s" % (e.tag, e.text) # how to change an element's text root.appointment.begin = "something else" print root.appointment.begin # how to add a new element root.appointment.new_element = "new data" # print the xml obj_xml = etree.tostring(root, pretty_print=True) print obj_xml # remove the py:pytype stuff #objectify.deannotate(root) etree.cleanup_namespaces(root) obj_xml = etree.tostring(root, pretty_print=True) print obj_xml # save your xml with open("new.xml", "w") as f: f.write(obj_xml) #---------------------------------------------------------------------- if __name__ == "__main__": f = r'path\to\sample.xml' parseXML(f) The code is pretty well commented, but we’ll spend a little time going over it anyway. First we pass it our sample XML file and objectify it. If you want to get access to a tag’s attributes, use the attrib property. It will return a dictionary of the attribute’s of the tag. To get to sub-tag elements, you just use dot notation. As you can see, to get to the begin tag’s value, we can just do something like this: begin = root.appointment.begin If you need to iterate over the children elements, you can use iterchildren. You may have to use a nested for loop structure to get everything. Changing an element’s value is as simple as just assigning it a new value. And if you need to create a new element, just add a period and the name of the new element (see below): root.appointment.new_element = "new data" When we add or change items using objectify, it will add some annotations to the XML, such as xmlns:py="http://codespeak.net/lxml/objectify/pytype" py:pytype="str". You may not want that included, so you'll have to call the following method to remove that stuff: [python] etree.cleanup_namespaces(root) You can also use “objectify.deannotate(root)” to do some deannotation chores, but I wasn’t able to get it to work for this example. To save the new XML, you actually seem to need lxml’s etree module to convert it to a string so you can save it. At this point, you should be able to parse most XML documents and edit them effectively with lxml’s objectify. I thought it was very intuitive and easy to pick up. Hopefully you will find it useful in your endeavors as well.

After my article Connection Pooling in a Java Web Application with Glassfish and NetBeans IDE, here are the instructions for Tomcat. Requirements NetBeans IDE (this tutorial uses NetBeans 7) Tomcat (this tutorial uses Tomcat 7 that is bundled within NetBeans) MySQL database MySQL Java Driver Steps Assuming your MySQL database is ready, connect to it and create a database. Lets call it connpool: mysql> create database connpool; Now we create and populate the table from which we will fetch the data: mysql> use connpool; mysql> create table data(id int(5) not null unique auto_increment, name varchar(255) not null); mysql> insert into data(name) values("Fred Flintstone"), ("Pink Panther"), ("Wayne Cramp"), ("Johnny Bravo"), ("Spongebob Squarepants"); That is it for the database part. We now create our web application. In NetBeans IDE, click File → New Project... Select Java Web → Web Application: Click Next and give the project the name TomPool. Click Next Choose the server as Tomcat and, since we are not going to use any frameworks, click Finish. The project will be created and the start page, index.jsp, opened for us in the IDE. Now we create the connection pooling parameters. In the Projects window, expand configuration files and open "context.xml". You will see that the IDE has added this code for us: Delete the last line: and then add the following to the context.xml file. I have explained the sections along the way. Make sure you edit your MySQL username and password appropriately: Next, expand the Web Pages node, right-click WEB-INF → New → Other → XML → XML Document. Click Next and type web for the File Name. Click next and choose Well-Formed Document then Finish. You will now have the file "web.xml": Delete everything in the file and paste this code: MySQL Test App DB Connection connpool javax.sql.DataSource Container That is it for the connection pool. We now edit our code to make use of it. Edit index.jsp by adding this code just after the initial coments but before Edit the section of the page: Data in my Connection Pooled Database Now, we test the connection pool by running the application: If you want to have the one connection pool used in multiple applications, you need to edit the following two files: 1. /conf/web.xml Just before the closing tag, add the code DB Connection connpool javax.sql.DataSource Container 2. /conf/context.xml Just before the closing tag, add the code Now you can use the pool without editing XML files in each of your applications. Just use the sample code as given in index.jsp That's it folks!

Some time ago I came across What's the purpose of AsyncContext.start(...) in Servlet 3.0? question. Quoting the Javadoc of aforementioned method: Causes the container to dispatch a thread, possibly from a managed thread pool, to run the specified Runnable. To remind all of you, AsyncContext is a standard way defined in Servlet 3.0 specification to handle HTTP requests asynchronously. Basically HTTP request is no longer tied to an HTTP thread, allowing us to handle it later, possibly using fewer threads. It turned out that the specification provides an API to handle asynchronous threads in a different thread pool out of the box. First we will see how this feature is completely broken and useless in Tomcat and Jetty - and then we will discuss why the usefulness of it is questionable in general. Our test servlet will simply sleep for given amount of time. This is a scalability killer in normal circumstances because even though sleeping servlet is not consuming CPU, but sleeping HTTP thread tied to that particular request consumes memory - and no other incoming request can use that thread. In our test setup I limited the number of HTTP worker threads to 10 which means only 10 concurrent requests are completely blocking the application (it is unresponsive from the outside) even though the application itself is almost completely idle. So clearly sleeping is an enemy of scalability. @WebServlet(urlPatterns = Array("/*")) class SlowServlet extends HttpServlet with Logging { protected override def doGet(req: HttpServletRequest, resp: HttpServletResponse) { logger.info("Request received") val sleepParam = Option(req.getParameter("sleep")) map {_.toLong} TimeUnit.MILLISECONDS.sleep(sleepParam getOrElse 10) logger.info("Request done") } } Benchmarking this code reveals that the average response times are close to sleep parameter as long as the number of concurrent connections is below the number of HTTP threads. Unsurprisingly the response times begin to grow the moment we exceed the HTTP threads count. Eleventh connection has to wait for any other request to finish and release worker thread. When the concurrency level exceeds 100, Tomcat begins to drop connections - too many clients are already queued. So what about the the fancy AsyncContext.start() method (do not confuse with ServletRequest.startAsync())? According to the JavaDoc I can submit any Runnable and the container will use some managed thread pool to handle it. This will help partially as I no longer block HTTP worker threads (but still another thread somewhere in the servlet container is used). Quickly switching to asynchronous servlet: @WebServlet(urlPatterns = Array("/*"), asyncSupported = true) class SlowServlet extends HttpServlet with Logging { protected override def doGet(req: HttpServletRequest, resp: HttpServletResponse) { logger.info("Request received") val asyncContext = req.startAsync() asyncContext.setTimeout(TimeUnit.MINUTES.toMillis(10)) asyncContext.start(new Runnable() { def run() { logger.info("Handling request") val sleepParam = Option(req.getParameter("sleep")) map {_.toLong} TimeUnit.MILLISECONDS.sleep(sleepParam getOrElse 10) logger.info("Request done") asyncContext.complete() } }) } } We are first enabling the asynchronous processing and then simply moving sleep() into a Runnable and hopefully a different thread pool, releasing the HTTP thread pool. Quick stress test reveals slightly unexpected results (here: response times vs. number of concurrent connections): Guess what, the response times are exactly the same as with no asynchronous support at all (!) After closer examination I discovered that when AsyncContext.start() is called Tomcat submits given task back to... HTTP worker thread pool, the same one that is used for all HTTP requests! This basically means that we have released one HTTP thread just to utilize another one milliseconds later (maybe even the same one). There is absolutely no benefit of calling AsyncContext.start() in Tomcat. I have no idea whether this is a bug or a feature. On one hand this is clearly not what the API designers intended. The servlet container was suppose to manage separate, independent thread pool so that HTTP worker thread pool is still usable. I mean, the whole point of asynchronous processing is to escape the HTTP pool. Tomcat pretends to delegate our work to another thread, while it still uses the original worker thread pool. So why I consider this to be a feature? Because Jetty is "broken" in exactly same way... No matter whether this works as designed or is only a poor API implementation, using AsyncContext.start() in Tomcat and Jetty is pointless and only unnecessarily complicates the code. It won't give you anything, the application works exactly the same under high load as if there was no asynchronous logic at all. But what about using this API feature on correct implementations like IBM WAS? It is better, but still the API as is doesn't give us much in terms of scalability. To explain again: the whole point of asynchronous processing is the ability to decouple HTTP request from an underlying thread, preferably by handling several connections using the same thread. AsyncContext.start() will run the provided Runnable in a separate thread pool. Your application is still responsive and can handle ordinary requests while long-running request that you decided to handle asynchronously are processed in a separate thread pool. It is better, unfortunately the thread pool and thread per connection idiom is still a bottle-neck. For the JVM it doesn't matter what type of threads are started - they still occupy memory. So we are no longer blocking HTTP worker threads, but our application is not more scalable in terms of concurrent long-running tasks we can support. In this simple and unrealistic example with sleeping servlet we can actually support thousand of concurrent (waiting) connections using Servlet 3.0 asynchronous support with only one extra thread - and without AsyncContext.start(). Do you know how? Hint: ScheduledExecutorService. Postscriptum: Scala goodness I almost forgot. Even though examples were written in Scala, I haven't used any cool language features yet. Here is one: implicit conversions. Make this available in your scope: implicit def blockToRunnable[T](block: => T) = new Runnable { def run() { block } } And suddenly you can use code block instead of instantiating Runnable manually and explicitly: asyncContext start { logger.info("Handling request") val sleepParam = Option(req.getParameter("sleep")) map { _.toLong} TimeUnit.MILLISECONDS.sleep(sleepParam getOrElse 10) logger.info("Request done") asyncContext.complete() } Sweet!

In my last two blog posts, I showed examples of using Selenium WebDriver to capture screenshots, and running in a headless (no X-server) mode. This example combines the two solutions to capture screenshots inside a virtual display. To achieve this, I use a combination of Selenium WebDriver and pyvirtualdisplay (which uses xvfb) to run a browser in a virtual display and capture screenshots. the setup you need is: Selenium 2 Python bindings: PyPI pyvirtualdisplay Python package (depends on xvfb): PyPI On Debian/Ubuntu Linux systems, you can install everything with: $ sudo apt-get install python-pip xvfb xserver-xephyr $ sudo pip install selenium once you have it setup, the following code example should work: #!/usr/bin/env python from pyvirtualdisplay import Display from selenium import webdriver display = Display(visible=0, size=(800, 600)) display.start() browser = webdriver.Firefox() browser.get('http://www.google.com') browser.save_screenshot('screenie.png') browser.quit() display.stop() this will: launch a virtual display launch Firefox browser inside the virtual display navigate to google.com capture and save a screenshot close the browser stop the virtual display

Introduction In recent times, many programming languages that run on JVM have emerged. Many of these languages support the concept of writing code in a functional style. Programmers have started realizing the benefits of functional programming and are beginning to rediscover the powerful style of this programming paradigm. The emergence of multiple languages on JVM have only helped to reignite the strong interest in this paradigm. Java at its core is an imperative programming language. However in recent past many new languages like Scala, Clojure, Groovy etc. have become popular which supports functional programming style and yet run on JVM. However none of these languages can be considered as pure functional language since all of them allow Java code to be called from within them and Java on its own is not a functional language. Still they have different degree of support for writing code in functional style and have their own benefits. Functional programming requires different kind of thinking and has its own advantages as compared to imperative programming. It seems that Java has also realized functional programming advantages and is slowly inching towards it. First sign of this can be seen in the form of Lambda Expressions that will be supported in Java 8. Although it's too early to comment on this as the draft for Java 8 is still under review and is expected to be released next year, but it does show that Java has plans of supporting functional programming style going forward. In this article we will first discuss what functional programming is and how it is different from imperative programming. Later we will see where does each of the above mentioned Java based programming languages i.e. Scala, Clojure and Groovy fits in the world of functional programming and what each of them has to offer. And at the last we will sneak-peak into Java 8's lambda expressions. Why Functional Programming? Computers of current era are shipped with multicore processors. Going forward the number of processors in a machine is only going to increase. The code we write today and tomorrow will probably never run on a single processor system. In order to get best out of this, software must be designed to make more and more use of concurrency and hence keep all available processors busy. Java does provide concurrency concepts like threads, synchronization, locks etc. to execute code in parallel. But shared memory multi-threading approach in Java causes more trouble than solving the problem. Java based functional programming languages like Scala, Clojure, Groovy etc. looks into these problems with a different angle and provides less complex and less error-prone solutions as compared to imperative programming. They provide immutability concepts out of the box and hence eliminate need of synchronization and associated risk of deadlocks or livelocks. Concepts like Actors, Agents and DataFlow variables provide high level concurrency abstraction and makes very easy to write concurrent programs. What is Functional Programming? Functional Programming is a concept which treats functions as first class citizens. At the core of functional programming is immutability. It emphasizes on application of functions in contrast to imperative programming style which emphasizes on change in state. Functional programming has no side effects whereas programming in imperative style can result in side-effects. Let's elaborate more on each of these characteristics to understand the concept behind functional programming. Immutable state - The state of an object doesn't change and hence need not be protected or synchronized. That might sound a bit awkward at first, since if nothing changes, one might think that we are not writing a useful program. However that's not what immutable state means. In functional programming, change in state occurs via series of transformations which keeps the object immutable and yet achieves change in state. Functions as first class citizens - There was a major shift in the way programs were written when Object oriented concepts came into picture. Everything was conceptualized as object and any action to be performed was treated as method call on objects. Hence there is a series of method calls executed on objects to get the desired work done. In functional programming world, it's more about thinking in terms of communication chain between functions than method calls on objects. This makes functions as first class citizens of functional programming since everything is modelled around functions. Higher-order functions - Functions in functional programming are higher order functions since following actions can be performed with them. 1. Functions can be passed within functions as arguments. 2. Functions can be created within functions just as objects can be created in functions 3. Functions can be returned from functions Functions with no side-effects - In functional programming, function execution has no side-effects. In other words a function code will always return same result for same argument when called multiple times. It doesn't change anything outside its boundaries and is also not affected by any external change outside it's boundary. It doesn't change input value and can only produce new output. However once the output has been produced and returned by function, it also becomes immutable and cannot be modified by any other function. In other words, they support referential transparency i.e. if a function takes an input and returns some output, multiple invocation of that function at different point of time will always return same output as long as input remains same. This is one of the main motivations behind using functional language as it makes easy to understand and predict behaviour of program. Characteristics like immutability and no side-effects are extremely helpful while writing multi-threaded code and developers need not to worry for synchronizing the state. Hence functional code is very easy to distribute across multiple cores as they don't have any side effects. JVM based Functional Programming Languages There are many JVM based languages which supports functional programming paradigm. However I intend to limit discussion around following. Scala Clojure Groovy Lambda Expressions in Java 8 Lambda Expressions is not a programming language but a feature that will be supported in Java8. The reason for including it in this article is to emphasize on the fact that going forward Java will also support writing code in functional style. Scala Scala is a statically typed multi-paradigm programming language designed to integrate features of object oriented programming and functional programming. Since it is static, one cannot change class definition at run time i.e. one cannot add new methods or variables at run-time. However Scala does provide functional programming concepts i.e. immutability, higher-order functions, nested functions etc. Apart from supporting Java's concurrency model, it also provides concept of Actor model out of the box for event based asynchronous message passing between objects. The code written in Scala gets compiled into very efficient bytecode which can then be executed on JVM. Creating immutable list in Scala is very simple and doesn't require any extra effort. "val" keyword does the trick. val numbers = List(1,2,3,4) Functions can be passed as arguments. Let's see this with an example. Suppose we have a list of 10 numbers and we want to calculate sum of all the numbers in list. val numbers = List(1,2,3,4,5,6,7,8,9,10) val total = numbers.foldLeft(0){(a,b) => a+b } As can be seen in above example, we are passing a function to add two variables "a" and "b" to another function "foldLeft" which is provided by Scala library on collections. We have also not used any iteration logic and temporary variable to calculate the sum. "foldLeft" method eliminates the need to maintain state in temporary variable which would have otherwise be required if we were to write this code in pure Java way (as mentioned below). int total = 0; for(int number in numbers){ total+=number; } Scala function can easily be executed in parallel without any need for synchronization since it does not mutate state. This was just a small example to showcase the power of Scala as functional programming language. There are whole lot of features available in Scala to write code in functional style. Clojure Clojure is a dynamic language with an excellent support for writing code in functional style. It is a dialect of "lisp" programming language with an efficient and robust infrastructure for multithreaded programming. Clojure is predominantly a functional programming language, and features a rich set of immutable, persistent data structures. When mutable state is needed, Clojure offers a software transactional memory system and reactive Agent system that ensure clean, correct multithreaded designs. Apart from this since Clojure is a dynamic language, it allows to modify class definition at run time by adding new methods or modifying existing one at run time. This makes it different from Scala which is a statically typed language. Immutability is in the root of Clojure. To create immutable list just following needs to be done. By default list in Clojure is immutable, so does not require any extra effort. (def numbers (list 1 2 3 4 5 6 7 8 9 10)) To add numbers without maintaining state, reduce function can be used as mentioned below (reduce + 0 '(1 2 3 4 5 6 7 8 9 10)) As can be seen, adding list of numbers just requires one line of code without mutating any state. This is the beauty about functional programming languages and plays an important role for parallel execution. Groovy Groovy is again a dynamic language with some support for functional programming. Amongst the 3 languages, Groovy can be considered weakest in terms of functional programming features. However because of it's dynamic nature and close resemblance to Java, it has been widely accepted and considered good alternative to Java. Groovy does not provide immutable objects out of the box but has excellent support for higher order functions. Immutable objects can be created with annotation @Immutation, but it's far less flexible than immutablity support in Scala and Clojure. In Groovy functions can be passed around just as any other variable in the form of Closures. The same example in Groovy can be written as follows def numbers = [1,2,3,4,5,6,7,8,9,10] def total = numbers.inject(0){a,b -> a+b } However the point to be noted is that variables "numbers" and "total" are not immutable and can be modified at any point of time. Hence writing multithreaded code can be a bit challenging. But Groovy does provide the concept of Actors, Agents and DataFlow variables via library called GPars(Groovy Parallel System) which reduces the challenges associated with multithreaded code to a greater extent. Java8 Lambda Expression Java has finally realized the power of writing code in functional style and is going to support the concept of closures starting from Java8. JSR 335 - Lambda Expressions for the JavaTM Programming Language aims to support programming in a multicore environment by adding closures and related features to the Java language. So it will finally be possible to pass around functions similar to variables in pure Java code. Currently if someone wants to try out and play around lambda expressions, Project Lambda of OpenJDK provides prototype implementation of JSR-335. Following code snippet should run fine with OpenJDK Project Lambda compiler. ExecutorService executor = Executors.newCachedThreadPool(); executor.submit(() -> {System.out.println("I am running")}) As can be seen above, a closure(function) has been passed to executor's submit method. It does not take any argument and hence empty brackets () have been placed. This function just prints "I am running" when executed. Just as we can pass functions to function, it will also be possible to create closure within functions and return closure from function. I would recommend to try out OpenJDK to get a feel of lambda expressions which is going to be part of Java8 Conclusion So this was all about functional programming, it's concepts, benefits and options available on JVM to write function code. Functional programming requires a different mind-set and can be very useful if used correctly. Functional Programming along with Object Oriented Programming can be a jewel in crown. As discussed there are various options available to write code in functional style that can be executed on JVM. Choice depends on various factors and there is no one language that can be considered best in all aspects. However one thing is for sure, going forward we are going to see more and more usage of functional programming.

At my employer we have a local NuGet server to host all of our internal packages. Occasionally, I’ll be working on a project and realize that I need to tweak something in one of my NuGet packages. Initially, I got into the habit of opening up a second instance of Visual Studio, making the necessary changes and using the NuGet web interface to re-upload the package. I quickly realized that manually uploading the package was too time consuming. Therefore, I started looking for a way to automate the process instead. Eventually that led me to the PowerShell script you see below. $nugetServer = "https://" $apiKey = "" $packageName = "" $latestRelease = nuget list $packageName $version = $latestRelease.split(" ")[1]; $versionTokens = $version.split(".") $buildNumber = [System.Double]::Parse($versionTokens[$versionTokens.Count -1]) $versionTokens[$versionTokens.Count -1] = $buildNumber +1 $newVersion = [string]::join('.', $versionTokens) echo $newVersion get-childitem | where {$_.extension -eq ".nupkg"} | foreach ($_) {remove-item $_.fullname} nuget pack -Version $newVersion $package = get-childitem | where {$_.extension -eq ".nupkg"} nuget push -Source $nugetServer $package $apiKey The script needs a few variables defined in order for it to run. The first variable ($nugetServer) is the URL of the NuGet Server. The second variable ($apiKey) is your personal API key. You can get your API key by logging into your NuGet Server with a browser. After you log in, click on your username in the upper right hand corner. This will take you to your account page. On the bottom of the “My Account” page there is a box which you can click on to make your API key visible. Finally the last variable ($packageName) is the name of the package you are uploading. This can be easily acquired by looking at your project properties and copying the Assembly name from the Application tab. Depending on how your machine is configured you may have the option to Run with PowerShell on your context menu. If not, you can take a look at this blog post in order to configure it manually. Alternatively you can use the following command instead. powershell.exe "\publish.ps1" If you have any problems running the script then please refer to the following TechNet article or send me a question and I’ll be glad to help.

Learn how Apache Camel implements the EIPs and offers a standardized, internal domain-specific language (DSL) to integrate applications.

This article will describe the complete root cause analysis of a recent Java deadlock problem observed from a Weblogic 11g production system running on the IBM JVM 1.6.This case study will also demonstrate the importance of mastering Thread Dump analysis skills; including for the IBM JVM Thread Dump format. Environment specification Java EE server: Oracle Weblogic Server 11g & Spring 2.0 OS: AIX 5.3 Java VM: IBM JRE 1.6.0 Platform type: Portal & ordering application Monitoring and troubleshooting tools JVM Thread Dump (IBM JVM format) Compuware Server Vantage (Weblogic JMX monitoring & alerting) Problem overview A major stuck Threads problem was observed & reported from Compuware Server Vantage and affecting 2 of our Weblogic 11g production managed servers causing application impact and timeout conditions from our end users. Gathering and validation of facts As usual, a Java EE problem investigation requires gathering of technical and non-technical facts so we can either derived other facts and/or conclude on the root cause. Before applying a corrective measure, the facts below were verified in order to conclude on the root cause: · What is the client impact? MEDIUM (only 2 managed servers / JVM affected out of 16) · Recent change of the affected platform? Yes (new JMS related asynchronous component) · Any recent traffic increase to the affected platform? No · How does this problem manifest itself? A sudden increase of Threads was observed leading to rapid Thread depletion · Did a Weblogic managed server restart resolve the problem? Yes, but problem is returning after few hours (unpredictable & intermittent pattern) - Conclusion #1: The problem is related to an intermittent stuck Threads behaviour affecting only a few Weblogic managed servers at the time - Conclusion #2: Since problem is intermittent, a global root cause such as a non-responsive downstream system is not likely Thread Dump analysis – first pass The first thing to do when dealing with stuck Thread problems is to generate a JVM Thread Dump. This is a golden rule regardless of your environment specifications & problem context. A JVM Thread Dump snapshot provides you with crucial information about the active Threads and what type of processing / tasks they are performing at that time. Now back to our case study, an IBM JVM Thread Dump (javacore.xyz format) was generated which did reveal the following Java Thread deadlock condition below: 1LKDEADLOCK Deadlock detected !!! NULL --------------------- NULL 2LKDEADLOCKTHR Thread "[STUCK] ExecuteThread: '8' for queue: 'weblogic.kernel.Default (self-tuning)'" (0x000000012CC08B00) 3LKDEADLOCKWTR is waiting for: 4LKDEADLOCKMON sys_mon_t:0x0000000126171DF8 infl_mon_t: 0x0000000126171E38: 4LKDEADLOCKOBJ weblogic/jms/frontend/FESession@0x07000000198048C0/0x07000000198048D8: 3LKDEADLOCKOWN which is owned by: 2LKDEADLOCKTHR Thread "[STUCK] ExecuteThread: '10' for queue: 'weblogic.kernel.Default (self-tuning)'" (0x000000012E560500) 3LKDEADLOCKWTR which is waiting for: 4LKDEADLOCKMON sys_mon_t:0x000000012884CD60 infl_mon_t: 0x000000012884CDA0: 4LKDEADLOCKOBJ weblogic/jms/frontend/FEConnection@0x0700000019822F08/0x0700000019822F20: 3LKDEADLOCKOWN which is owned by: 2LKDEADLOCKTHR Thread "[STUCK] ExecuteThread: '8' for queue: 'weblogic.kernel.Default (self-tuning)'" (0x000000012CC08B00) This deadlock situation can be translated as per below: - Weblogic Thread #8 is waiting to acquire an Object monitor lock owned by Weblogic Thread #10 - Weblogic Thread #10 is waiting to acquire an Object monitor lock owned by Weblogic Thread #8 Conclusion: both Weblogic Threads #8 & #10 are waiting on each other; forever! Now before going any deeper in this root cause analysis, let me provide you a high level overview on Java Thread deadlocks. Java Thread deadlock overview Most of you are probably familiar with Java Thread deadlock principles but did you really experience a true deadlock problem? From my experience, true Java deadlocks are rare and I have only seen ~5 occurrences over the last 10 years. The reason is that most stuck Threads related problems are due to Thread hanging conditions (waiting on remote IO call etc.) but not involved in a true deadlock condition with other Thread(s). A Java Thread deadlock is a situation for example where Thread A is waiting to acquire an Object monitor lock held by Thread B which is itself waiting to acquire an Object monitor lock held by Thread A. Both these Threads will wait for each other forever. This situation can be visualized as per below diagram: Thread deadlock is confirmed…now what can you do? Once the deadlock is confirmed (most JVM Thread Dump implementations will highlight it for you), the next step is to perform a deeper dive analysis by reviewing each Thread involved in the deadlock situation along with their current task & wait condition.Find below the partial Thread Stack Trace from our problem case for each Thread involved in the deadlock condition: ** Please note that the real application Java package name was renamed for confidentiality purposes ** Weblogic Thread #8 "[STUCK] ExecuteThread: '8' for queue: 'weblogic.kernel.Default (self-tuning)'" J9VMThread:0x000000012CC08B00, j9thread_t:0x00000001299E5100, java/lang/Thread:0x070000001D72EE00, state:B, prio=1 (native thread ID:0x111200F, native priority:0x1, native policy:UNKNOWN) Java callstack: at weblogic/jms/frontend/FEConnection.stop(FEConnection.java:671(Compiled Code)) at weblogic/jms/frontend/FEConnection.invoke(FEConnection.java:1685(Compiled Code)) at weblogic/messaging/dispatcher/Request.wrappedFiniteStateMachine(Request.java:961(Compiled Code)) at weblogic/messaging/dispatcher/DispatcherImpl.syncRequest(DispatcherImpl.java:184(Compiled Code)) at weblogic/messaging/dispatcher/DispatcherImpl.dispatchSync(DispatcherImpl.java:212(Compiled Code)) at weblogic/jms/dispatcher/DispatcherAdapter.dispatchSync(DispatcherAdapter.java:43(Compiled Code)) at weblogic/jms/client/JMSConnection.stop(JMSConnection.java:863(Compiled Code)) at weblogic/jms/client/WLConnectionImpl.stop(WLConnectionImpl.java:843) at org/springframework/jms/connection/SingleConnectionFactory.closeConnection(SingleConnectionFactory.java:342) at org/springframework/jms/connection/SingleConnectionFactory.resetConnection(SingleConnectionFactory.java:296) at org/app/JMSReceiver.receive() …………………………………………………………………… Weblogic Thread #10 "[STUCK] ExecuteThread: '10' for queue: 'weblogic.kernel.Default (self-tuning)'" J9VMThread:0x000000012E560500, j9thread_t:0x000000012E35BCE0, java/lang/Thread:0x070000001ECA9200, state:B, prio=1 (native thread ID:0x4FA027, native priority:0x1, native policy:UNKNOWN) Java callstack: at weblogic/jms/frontend/FEConnection.getPeerVersion(FEConnection.java:1381(Compiled Code)) at weblogic/jms/frontend/FESession.setUpBackEndSession(FESession.java:755(Compiled Code)) at weblogic/jms/frontend/FESession.consumerCreate(FESession.java:1025(Compiled Code)) at weblogic/jms/frontend/FESession.invoke(FESession.java:2995(Compiled Code)) at weblogic/messaging/dispatcher/Request.wrappedFiniteStateMachine(Request.java:961(Compiled Code)) at weblogic/messaging/dispatcher/DispatcherImpl.syncRequest(DispatcherImpl.java:184(Compiled Code)) at weblogic/messaging/dispatcher/DispatcherImpl.dispatchSync(DispatcherImpl.java:212(Compiled Code)) at weblogic/jms/dispatcher/DispatcherAdapter.dispatchSync(DispatcherAdapter.java:43(Compiled Code)) at weblogic/jms/client/JMSSession.consumerCreate(JMSSession.java:2982(Compiled Code)) at weblogic/jms/client/JMSSession.setupConsumer(JMSSession.java:2749(Compiled Code)) at weblogic/jms/client/JMSSession.createConsumer(JMSSession.java:2691(Compiled Code)) at weblogic/jms/client/JMSSession.createReceiver(JMSSession.java:2596(Compiled Code)) at weblogic/jms/client/WLSessionImpl.createReceiver(WLSessionImpl.java:991(Compiled Code)) at org/springframework/jms/core/JmsTemplate102.createConsumer(JmsTemplate102.java:204(Compiled Code)) at org/springframework/jms/core/JmsTemplate.doReceive(JmsTemplate.java:676(Compiled Code)) at org/springframework/jms/core/JmsTemplate$10.doInJms(JmsTemplate.java:652(Compiled Code)) at org/springframework/jms/core/JmsTemplate.execute(JmsTemplate.java:412(Compiled Code)) at org/springframework/jms/core/JmsTemplate.receiveSelected(JmsTemplate.java:650(Compiled Code)) at org/springframework/jms/core/JmsTemplate.receiveSelected(JmsTemplate.java:641(Compiled Code)) at org/app/JMSReceiver.receive() …………………………………………………………… As you can see in the above Thread Strack Traces, such deadlock did originate from our application code which is using the Spring framework API for the JMS consumer implementation (very useful when not using MDB’s). The Stack Traces are quite interesting and revealing that both Threads are in a race condition against the same Weblogic JMS consumer session / connection and leading to a deadlock situation: - Weblogic Thread #8 is attempting to reset and close the current JMS connection - Weblogic Thread #10 is attempting to use the same JMS Connection / Session in order to create a new JMS consumer - Thread deadlock is triggered! Root cause: non Thread safe Spring JMS SingleConnectionFactory implementation A code review and a quick research from Spring JIRA bug database did reveal the following Thread safe defect below with a perfect correlation with the above analysis: # SingleConnectionFactory's resetConnection is causing deadlocks with underlying OracleAQ's JMS connection https://jira.springsource.org/browse/SPR-5987 A patch for Spring SingleConnectionFactory was released back in 2009 which did involve adding proper synchronized{} block in order to prevent Thread deadlock in the event of a JMS Connection reset operation: synchronized (connectionMonitor) { //if condition added to avoid possible deadlocks when trying to reset the target connection if (!started) { this.target.start(); started = true; } } Solution Our team is currently planning to integrate this Spring patch in to our production environment shortly. The initial tests performed in our test environment are positive. Conclusion I hope this case study has helped understand a real-life Java Thread deadlock problem and how proper Thread Dump analysis skills can allow you to quickly pinpoint the root cause of stuck Thread related problems at the code level. Please don’t hesitate to post any comment or question.

Cross-site request forgery attacks (CSRF) are very common in web applications and can cause significant harm if allowed. If you have never heard of CSRF I recommend you check out OWASPs page about it. Luckily preventing CSRF attacks is quite simple, I’ll try to show you how they work and how we can defend from them in the least obtrusive way possible in Java based web apps. Imagine you are about to perform a money transfer in your bank’s secure web page, when you click on the transfer option a form page is loaded that allows you to choose the debit and credit accounts, and enter the amount of money to move. When you are satisfied with your options you press “submit” and send the form information to your bank’s web server, which in turns performs the transaction. Now add the following to the picture, a malicious website (which you think harmless of course) is open on another window/tab of your browser while you are innocently moving all your millions in your bank’s site. This evil site knows the bank’s web forms structure, and as you browse through it, it tries to post transactions withdrawing money from your accounts and depositing it on the evil overlord’s accounts, it can do it because you have an open and valid session with the banks site in the same browser! This is the basis for a CSRF attack. One simple and effective way to prevent it is to generate a random (i.e. unpredictable) string when the initial transfer form is loaded and send it to the browser. The browser then sends this piece of data along with the transfer options, and the server validates it before approving the transaction for processing. This way, malicious websites cannot post transactions even if they have access to a valid session in a browser. To implement this mechanism in Java I choose to use two filters, one to create the salt for each request, and another to validate it. Since the users request and subsequent POST or GETs that should be validated do not necessarily get executed in order, I decided to use a time based cache to store a list of valid salt strings. The first filter, used to generate a new salt for a request and store it in the cache can be coded as follows: package com.ricardozuasti.csrf; import com.google.common.cache.Cache; import com.google.common.cache.CacheBuilder; import com.google.common.cache.CacheLoader; import com.google.common.cache.LoadingCache; import java.io.IOException; import java.security.SecureRandom; import java.util.concurrent.ExecutionException; import java.util.concurrent.TimeUnit; import javax.servlet.*; import javax.servlet.http.HttpServletRequest; import org.apache.commons.lang.RandomStringUtils; public class LoadSalt implements Filter { @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // Assume its HTTP HttpServletRequest httpReq = (HttpServletRequest) request; // Check the user session for the salt cache, if none is present we create one Cache csrfPreventionSaltCache = (Cache) httpReq.getSession().getAttribute("csrfPreventionSaltCache"); if (csrfPreventionSaltCache == null){ csrfPreventionSaltCache = CacheBuilder.newBuilder() .maximumSize(5000) .expireAfterWrite(20, TimeUnit.MINUTES) .build(); httpReq.getSession().setAttribute("csrfPreventionSaltCache", csrfPreventionSaltCache); } // Generate the salt and store it in the users cache String salt = RandomStringUtils.random(20, 0, 0, true, true, null, new SecureRandom()); csrfPreventionSaltCache.put(salt, Boolean.TRUE); // Add the salt to the current request so it can be used // by the page rendered in this request httpReq.setAttribute("csrfPreventionSalt", salt); chain.doFilter(request, response); } @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void destroy() { } } I used Guava CacheBuilder to create the salt cache since it has both a size limit and an expiration timeout per entry. To generate the actual salt I used Apache Commons RandomStringUtils, powered by Java 6 SecureRandom to ensure a strong generation seed. This filter should be used in all requests ending in a page that will link, post or call via AJAX a secured transaction, so in most cases it’s a good idea to map it to every request (maybe with the exception of static content such as images, CSS, etc.). It’s mapping in your web.xml should look similar to: ... loadSalt com.ricardozuasti.csrf.LoadSalt ... loadSalt * ... As I said, to validate the salt before executing secure transactions we can write another filter: package com.ricardozuasti.csrf; import com.google.common.cache.Cache; import java.io.IOException; import javax.servlet.*; import javax.servlet.http.HttpServletRequest; public class ValidateSalt implements Filter { @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // Assume its HTTP HttpServletRequest httpReq = (HttpServletRequest) request; // Get the salt sent with the request String salt = (String) httpReq.getParameter("csrfPreventionSalt"); // Validate that the salt is in the cache Cache csrfPreventionSaltCache = (Cache) httpReq.getSession().getAttribute("csrfPreventionSaltCache"); if (csrfPreventionSaltCache != null && salt != null && csrfPreventionSaltCache.getIfPresent(salt) != null){ // If the salt is in the cache, we move on chain.doFilter(request, response); } else { // Otherwise we throw an exception aborting the request flow throw new ServletException("Potential CSRF detected!! Inform a scary sysadmin ASAP."); } } @Override public void init(FilterConfig filterConfig) throws ServletException { } @Override public void destroy() { } } You should configure this filter for every request that needs to be secure (i.e. retrieves or modifies sensitive information, move money, etc.), for example: ... validateSalt com.ricardozuasti.csrf.ValidateSalt ... validateSalt /transferMoneyServlet ... After configuring both servlets all your secured requests should fail :). To fix it you have to add, to each link and form post that ends in a secure URL, the csrfPreventionSalt parameter containing the value of the request parameter with the same name. For example, in an HTML form within a JSP page: ... ... ... Of course you can write a custom tag, a nice Javascript code or whatever you prefer to inject the new parameter in every needed link/form.