Spring Batch Tutorial with Spring Boot and Java Configuration
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Join For FreeI’ve been working on migrating some batch jobs for Podcastpedia.org to Spring Batch. Before, these jobs were developed in my own kind of way, and I thought it was high time to use a more “standardized” approach. Because I had never used Spring with java configuration before, I thought this were a good opportunity to learn about it, by configuring the Spring Batch jobs in java. And since I am all into trying new things with Spring, why not also throw Spring Boot into the boat…
Before you begin with this tutorial I recommend you read first Spring’s Getting started – Creating a Batch Service, because the structure and the code presented here builds on that original.
1. What I’ll build
So, as mentioned, in this post I will present Spring Batch in the context of configuring it and developing with it some batch jobs for Podcastpedia.org. Here’s a short description of the two jobs that are currently part of the Podcastpedia-batch project:
- addNewPodcastJob
- reads podcast metadata (feed url, identifier, categories etc.) from a flat file
- transforms (parses and prepares episodes to be inserted with Http Apache Client) the data
- and in the last step, insert it to the Podcastpedia database and inform the submitter via emailabout it
- notifyEmailSubscribersJob – people can subscribe to their favorite podcasts on Podcastpedia.orgvia email. For those who did it is checked on a regular basis (DAILY, WEEKLY, MONTHLY) if new episodes are available, and if they are the subscribers are informed via email about those; read from database, expand read data via JPA, re-group it and notify subscriber via email
Source code:
The source code for this tutorial is available on GitHub – Podcastpedia-batch.
Note: Before you start I also highly recommend you read the Domain Language of Batch, so that terms like “Jobs”, “Steps” or “ItemReaders” don’t sound strange to you.
2. What you’ll need
- A favorite text editor or IDE
- JDK 1.7 or later
- Maven 3.0+
3. Set up the project
The project is built with Maven. It uses Spring Boot, which makes it easy to create stand-alone Spring based Applications that you can “just run”. You can learn more about the Spring Boot by visiting theproject’s website.
3.1. Maven build file
Because it uses Spring Boot it will have the spring-boot-starter-parent
as its parent, and a couple of other spring-boot-starters that will get for us some libraries required in the project:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.podcastpedia.batch</groupId> <artifactId>podcastpedia-batch</artifactId> <version>0.1.0</version> <properties> <sprinb.boot.version>1.1.6.RELEASE</sprinb.boot.version> <java.version>1.7</java.version> </properties> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>1.1.6.RELEASE</version> </parent> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-batch</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>4.3.5</version> </dependency> <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpcore</artifactId> <version>4.3.2</version> </dependency> <!-- velocity --> <dependency> <groupId>org.apache.velocity</groupId> <artifactId>velocity</artifactId> <version>1.7</version> </dependency> <dependency> <groupId>org.apache.velocity</groupId> <artifactId>velocity-tools</artifactId> <version>2.0</version> <exclusions> <exclusion> <groupId>org.apache.struts</groupId> <artifactId>struts-core</artifactId> </exclusion> </exclusions> </dependency> <!-- Project rome rss, atom --> <dependency> <groupId>rome</groupId> <artifactId>rome</artifactId> <version>1.0</version> </dependency> <!-- option this fetcher thing --> <dependency> <groupId>rome</groupId> <artifactId>rome-fetcher</artifactId> <version>1.0</version> </dependency> <dependency> <groupId>org.jdom</groupId> <artifactId>jdom</artifactId> <version>1.1</version> </dependency> <!-- PID 1 --> <dependency> <groupId>xerces</groupId> <artifactId>xercesImpl</artifactId> <version>2.9.1</version> </dependency> <!-- MySQL JDBC connector --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.31</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-freemarker</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-remote-shell</artifactId> <exclusions> <exclusion> <groupId>javax.mail</groupId> <artifactId>mail</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>javax.mail</groupId> <artifactId>mail</artifactId> <version>1.4.7</version> </dependency> <dependency> <groupId>javax.inject</groupId> <artifactId>javax.inject</artifactId> <version>1</version> </dependency> <dependency> <groupId>org.twitter4j</groupId> <artifactId>twitter4j-core</artifactId> <version>[4.0,)</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <artifactId>maven-compiler-plugin</artifactId> </plugin> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>
Note: One big advantage of using thespring-boot-starter-parent
as the project’s parent is that you only have to upgrade the version of the parent and it will get the “latest” libraries for you. When I started the project spring boot was in version1.1.3.RELEASE
and by the time of finishing to write this post is already at1.1.6.RELEASE
.
3.2. Project directory structure
I structured the project in the following way:
└── src └── main └── java └── org └── podcastpedia └── batch └── common └── jobs └── addpodcast └── notifysubscribers
Note:
- the
org.podcastpedia.batch.jobs
package contains sub-packages having specific classes to particular jobs. - the
org.podcastpedia.batch.jobs.common
package contains classes used by all the jobs, like for example the JPA entities that both the current jobs require.
4. Create a batch Job configuration
I will start by presenting the Java configuration class for the first batch job:
package org.podcastpedia.batch.jobs.addpodcast; import org.podcastpedia.batch.common.configuration.DatabaseAccessConfiguration; import org.podcastpedia.batch.common.listeners.LogProcessListener; import org.podcastpedia.batch.common.listeners.ProtocolListener; import org.podcastpedia.batch.jobs.addpodcast.model.SuggestedPodcast; import org.springframework.batch.core.Job; import org.springframework.batch.core.Step; import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing; import org.springframework.batch.core.configuration.annotation.JobBuilderFactory; import org.springframework.batch.core.configuration.annotation.StepBuilderFactory; import org.springframework.batch.item.ItemProcessor; import org.springframework.batch.item.ItemReader; import org.springframework.batch.item.ItemWriter; import org.springframework.batch.item.file.FlatFileItemReader; import org.springframework.batch.item.file.LineMapper; import org.springframework.batch.item.file.mapping.BeanWrapperFieldSetMapper; import org.springframework.batch.item.file.mapping.DefaultLineMapper; import org.springframework.batch.item.file.transform.DelimitedLineTokenizer; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Import; import org.springframework.core.io.ClassPathResource; import com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException; @Configuration @EnableBatchProcessing @Import({DatabaseAccessConfiguration.class, ServicesConfiguration.class}) public class AddPodcastJobConfiguration { @Autowired private JobBuilderFactory jobs; @Autowired private StepBuilderFactory stepBuilderFactory; // tag::jobstep[] @Bean public Job addNewPodcastJob(){ return jobs.get("addNewPodcastJob") .listener(protocolListener()) .start(step()) .build(); } @Bean public Step step(){ return stepBuilderFactory.get("step") .<SuggestedPodcast,SuggestedPodcast>chunk(1) //important to be one in this case to commit after every line read .reader(reader()) .processor(processor()) .writer(writer()) .listener(logProcessListener()) .faultTolerant() .skipLimit(10) //default is set to 0 .skip(MySQLIntegrityConstraintViolationException.class) .build(); } // end::jobstep[] // tag::readerwriterprocessor[] @Bean public ItemReader<SuggestedPodcast> reader(){ FlatFileItemReader<SuggestedPodcast> reader = new FlatFileItemReader<SuggestedPodcast>(); reader.setLinesToSkip(1);//first line is title definition reader.setResource(new ClassPathResource("suggested-podcasts.txt")); reader.setLineMapper(lineMapper()); return reader; } @Bean public LineMapper<SuggestedPodcast> lineMapper() { DefaultLineMapper<SuggestedPodcast> lineMapper = new DefaultLineMapper<SuggestedPodcast>(); DelimitedLineTokenizer lineTokenizer = new DelimitedLineTokenizer(); lineTokenizer.setDelimiter(";"); lineTokenizer.setStrict(false); lineTokenizer.setNames(new String[]{"FEED_URL", "IDENTIFIER_ON_PODCASTPEDIA", "CATEGORIES", "LANGUAGE", "MEDIA_TYPE", "UPDATE_FREQUENCY", "KEYWORDS", "FB_PAGE", "TWITTER_PAGE", "GPLUS_PAGE", "NAME_SUBMITTER", "EMAIL_SUBMITTER"}); BeanWrapperFieldSetMapper<SuggestedPodcast> fieldSetMapper = new BeanWrapperFieldSetMapper<SuggestedPodcast>(); fieldSetMapper.setTargetType(SuggestedPodcast.class); lineMapper.setLineTokenizer(lineTokenizer); lineMapper.setFieldSetMapper(suggestedPodcastFieldSetMapper()); return lineMapper; } @Bean public SuggestedPodcastFieldSetMapper suggestedPodcastFieldSetMapper() { return new SuggestedPodcastFieldSetMapper(); } /** configure the processor related stuff */ @Bean public ItemProcessor<SuggestedPodcast, SuggestedPodcast> processor() { return new SuggestedPodcastItemProcessor(); } @Bean public ItemWriter<SuggestedPodcast> writer() { return new Writer(); } // end::readerwriterprocessor[] @Bean public ProtocolListener protocolListener(){ return new ProtocolListener(); } @Bean public LogProcessListener logProcessListener(){ return new LogProcessListener(); } }
The @EnableBatchProcessing
annotation adds many critical beans that support jobs and saves us configuration work. For example you will also be able to @Autowired
some useful stuff into your context:
- a
JobRepository
(bean name “jobRepository”) - a
JobLauncher
(bean name “jobLauncher”) - a
JobRegistry
(bean name “jobRegistry”) - a
PlatformTransactionManager
(bean name “transactionManager”) - a
JobBuilderFactory
(bean name “jobBuilders”) as a convenience to prevent you from having to inject the job repository into every job, as in the examples above - a
StepBuilderFactory
(bean name “stepBuilders”) as a convenience to prevent you from having to inject the job repository and transaction manager into every step
The first part focuses on the actual job configuration:
@Bean public Job addNewPodcastJob(){ return jobs.get("addNewPodcastJob") .listener(protocolListener()) .start(step()) .build(); } @Bean public Step step(){ return stepBuilderFactory.get("step") .<SuggestedPodcast,SuggestedPodcast>chunk(1) //important to be one in this case to commit after every line read .reader(reader()) .processor(processor()) .writer(writer()) .listener(logProcessListener()) .faultTolerant() .skipLimit(10) //default is set to 0 .skip(MySQLIntegrityConstraintViolationException.class) .build(); }
The first method defines a job and the second one defines a single step. As you’ve read in The Domain Language of Batch, jobs are built from steps, where each step can involve a reader, a processor, and a writer.
In the step definition, you define how much data to write at a time (in our case 1 record at a time). Next you specify the reader, processor and writer.
5. Spring Batch processing units
Most of the batch processing can be described as reading data, doing some transformation on it and then writing the result out. This mirrors somehow the Extract, Transform, Load (ETL) process, in case you know more about that. Spring Batch provides three key interfaces to help perform bulk reading and writing: ItemReader
, ItemProcessor
and ItemWriter
.
5.1. Readers
ItemReader is an abstraction providing the mean to retrieve data from many different types of input: flat files, xml files, database, jms etc., one item at a time. See the Appendix A. List of ItemReaders and ItemWriters for a complete list of available item readers.
In the Podcastpedia batch jobs I use the following specialized ItemReaders:
5.1.1. FlatFileItemReader
which, as the name implies, reads lines of data from a flat file that typically describe records with fields of data defined by fixed positions in the file or delimited by some special character (e.g. Comma). This type of ItemReader
is being used in the first batch job, addNewPodcastJob. The input file used is named suggested-podcasts.in, resides in the classpath (src/main/resources) and looks something like the following:
FEED_URL; IDENTIFIER_ON_PODCASTPEDIA; CATEGORIES; LANGUAGE; MEDIA_TYPE; UPDATE_FREQUENCY; KEYWORDS; FB_PAGE; TWITTER_PAGE; GPLUS_PAGE; NAME_SUBMITTER; EMAIL_SUBMITTER http://www.5minutebiographies.com/feed/; 5minutebiographies; people_society, history; en; Audio; WEEKLY; biography, biographies, short biography, short biographies, 5 minute biographies, five minute biographies, 5 minute biography, five minute biography; https://www.facebook.com/5minutebiographies;https://twitter.com/5MinuteBios; ; Adrian Matei; adrianmatei@gmail.com http://notanotherpodcast.libsyn.com/rss; NotAnotherPodcast; entertainment; en; Audio; WEEKLY; Comedy, Sports, Cinema, Movies, Pop Culture, Food, Games; https://www.facebook.com/notanotherpodcastusa;https://twitter.com/NAPodcastUSA;https://plus.google.com/u/0/103089891373760354121/posts; Adrian Matei; adrianmatei@gmail.com
As you can see the first line defines the names of the “columns”, and the following lines contain the actual data (delimited by “;”), that needs translating to domain objects relevant in the context.
Let’s see now how to configure the FlatFileItemReader
:
@Bean public ItemReader<SuggestedPodcast> reader(){ FlatFileItemReader<SuggestedPodcast> reader = new FlatFileItemReader<SuggestedPodcast>(); reader.setLinesToSkip(1);//first line is title definition reader.setResource(new ClassPathResource("suggested-podcasts.in")); reader.setLineMapper(lineMapper()); return reader; }
You can specify, among other things, the input resource, the number of lines to skip, and a line mapper.
5.1.1.1. LineMapper
The LineMapper
is an interface for mapping lines (strings) to domain objects, typically used to map lines read from a file to domain objects on a per line basis. For the Podcastpedia job I used the DefaultLineMapper
, which is two-phase implementation consisting of tokenization of the line into a FieldSet
followed by mapping to item:
@Bean public LineMapper<SuggestedPodcast> lineMapper() { DefaultLineMapper<SuggestedPodcast> lineMapper = new DefaultLineMapper<SuggestedPodcast>(); DelimitedLineTokenizer lineTokenizer = new DelimitedLineTokenizer(); lineTokenizer.setDelimiter(";"); lineTokenizer.setStrict(false); lineTokenizer.setNames(new String[]{"FEED_URL", "IDENTIFIER_ON_PODCASTPEDIA", "CATEGORIES", "LANGUAGE", "MEDIA_TYPE", "UPDATE_FREQUENCY", "KEYWORDS", "FB_PAGE", "TWITTER_PAGE", "GPLUS_PAGE", "NAME_SUBMITTER", "EMAIL_SUBMITTER"}); BeanWrapperFieldSetMapper<SuggestedPodcast> fieldSetMapper = new BeanWrapperFieldSetMapper<SuggestedPodcast>(); fieldSetMapper.setTargetType(SuggestedPodcast.class); lineMapper.setLineTokenizer(lineTokenizer); lineMapper.setFieldSetMapper(suggestedPodcastFieldSetMapper()); return lineMapper; }
- the
DelimitedLineTokenizer
splits the input String via the “;” delimiter. - if you set the
strict
flag tofalse
then lines with less tokens will be tolerated and padded with empty columns, and lines with more tokens will simply be truncated. - the columns names from the first line are set
lineTokenizer.setNames(...);
- and the
fieldMapper
is set (line 14)
Note:
TheFieldSet
is an “interface used by flat file input sources to encapsulate concerns of converting an array of Strings to Java native types. A bit like the role played byResultSet
in JDBC, clients will know the name or position of strongly typed fields that they want to extract.“
5.1.1.2. FieldSetMapper
The FieldSetMapper
is an interface that is used to map data obtained from a FieldSet
into an object. Here’s my implementation which maps the fieldSet to the SuggestedPodcast
domain object that will be further passed to the processor:
public class SuggestedPodcastFieldSetMapper implements FieldSetMapper<SuggestedPodcast> { @Override public SuggestedPodcast mapFieldSet(FieldSet fieldSet) throws BindException { SuggestedPodcast suggestedPodcast = new SuggestedPodcast(); suggestedPodcast.setCategories(fieldSet.readString("CATEGORIES")); suggestedPodcast.setEmail(fieldSet.readString("EMAIL_SUBMITTER")); suggestedPodcast.setName(fieldSet.readString("NAME_SUBMITTER")); suggestedPodcast.setTags(fieldSet.readString("KEYWORDS")); //some of the attributes we can map directly into the Podcast entity that we'll insert later into the database Podcast podcast = new Podcast(); podcast.setUrl(fieldSet.readString("FEED_URL")); podcast.setIdentifier(fieldSet.readString("IDENTIFIER_ON_PODCASTPEDIA")); podcast.setLanguageCode(LanguageCode.valueOf(fieldSet.readString("LANGUAGE"))); podcast.setMediaType(MediaType.valueOf(fieldSet.readString("MEDIA_TYPE"))); podcast.setUpdateFrequency(UpdateFrequency.valueOf(fieldSet.readString("UPDATE_FREQUENCY"))); podcast.setFbPage(fieldSet.readString("FB_PAGE")); podcast.setTwitterPage(fieldSet.readString("TWITTER_PAGE")); podcast.setGplusPage(fieldSet.readString("GPLUS_PAGE")); suggestedPodcast.setPodcast(podcast); return suggestedPodcast; } }
5.2. JdbcCursorItemReader
In the second job, notifyEmailSubscribersJob, in the reader, I only read email subscribers from a single database table, but further in the processor a more detailed read(via JPA) is executed to retrieve all the new episodes of the podcasts the user subscribed to. This is a common pattern employed in the batch world. Follow this link for more Common Batch Patterns.
For the initial read, I chose the JdbcCursorItemReader
, which is a simple reader implementation that opens a JDBC cursor and continually retrieves the next row in the ResultSet
:
@Bean public ItemReader<User> notifySubscribersReader(){ JdbcCursorItemReader<User> reader = new JdbcCursorItemReader<User>(); String sql = "select * from users where is_email_subscriber is not null"; reader.setSql(sql); reader.setDataSource(dataSource); reader.setRowMapper(rowMapper()); return reader; }
Note I had to set the sql
, the datasource
to read from and a RowMapper
.
5.2.1. RowMapper
The RowMapper
is an interface used by JdbcTemplate
for mapping rows of a Result’set on a per-row basis. My implementation of this interface, , performs the actual work of mapping each row to a result object, but I don’t need to worry about exception handling:
public class UserRowMapper implements RowMapper<User> { @Override public User mapRow(ResultSet rs, int rowNum) throws SQLException { User user = new User(); user.setEmail(rs.getString("email")); return user; } }
5.2. Writers
ItemWriter
is an abstraction that represents the output of a Step
, one batch or chunk of items at a time. Generally, an item writer has no knowledge of the input it will receive next, only the item that was passed in its current invocation.
The writers for the two jobs presented are quite simple. They just use external services to send email notifications and post tweets on Podcastpedia’s account. Here is the implementation of the ItemWriter
for the first job – addNewPodcast:
package org.podcastpedia.batch.jobs.addpodcast; import java.util.Date; import java.util.List; import javax.inject.Inject; import javax.persistence.EntityManager; import org.podcastpedia.batch.common.entities.Podcast; import org.podcastpedia.batch.jobs.addpodcast.model.SuggestedPodcast; import org.podcastpedia.batch.jobs.addpodcast.service.EmailNotificationService; import org.podcastpedia.batch.jobs.addpodcast.service.SocialMediaService; import org.springframework.batch.item.ItemWriter; import org.springframework.beans.factory.annotation.Autowired; public class Writer implements ItemWriter<SuggestedPodcast>{ @Autowired private EntityManager entityManager; @Inject private EmailNotificationService emailNotificationService; @Inject private SocialMediaService socialMediaService; @Override public void write(List<? extends SuggestedPodcast> items) throws Exception { if(items.get(0) != null){ SuggestedPodcast suggestedPodcast = items.get(0); //first insert the data in the database Podcast podcast = suggestedPodcast.getPodcast(); podcast.setInsertionDate(new Date()); entityManager.persist(podcast); entityManager.flush(); //notify submitter about the insertion and post a twitt about it String url = buildUrlOnPodcastpedia(podcast); emailNotificationService.sendPodcastAdditionConfirmation( suggestedPodcast.getName(), suggestedPodcast.getEmail(), url); if(podcast.getTwitterPage() != null){ socialMediaService.postOnTwitterAboutNewPodcast(podcast, url); } } } private String buildUrlOnPodcastpedia(Podcast podcast) { StringBuffer urlOnPodcastpedia = new StringBuffer( "http://www.podcastpedia.org"); if (podcast.getIdentifier() != null) { urlOnPodcastpedia.append("/" + podcast.getIdentifier()); } else { urlOnPodcastpedia.append("/podcasts/"); urlOnPodcastpedia.append(String.valueOf(podcast.getPodcastId())); urlOnPodcastpedia.append("/" + podcast.getTitleInUrl()); } String url = urlOnPodcastpedia.toString(); return url; } }
As you can see there’s nothing special here, except that the write
method has to be overriden and this is where the injected external services EmailNotificationService
and SocialMediaService
are used to inform via email the podcast submitter about the addition to the podcast directory, and if a Twitter page was submitted a tweet will be posted on the Podcastpedia’s wall. You can find detailed explanation on how to send email via Velocity and how to post on Twitter from Java in the following posts:
- How to compose html emails in Java with Spring and Velocity
- How to post to Twittter from Java with Twitter4J in 10 minutes
5.3. Processors
ItemProcessor
is an abstraction that represents the business processing of an item. While theItemReader
reads one item, and the ItemWriter
writes them, the ItemProcessor
provides access to transform or apply other business processing. When using your own Processors
you have to implement the ItemProcessor<I,O>
interface, with its only method O process(I item) throws Exception
, returning a potentially modified or a new item for continued processing. If the returned result is null, it is assumed that processing of the item should not continue.
While the processor of the first job requires a little bit of more logic, because I have to set the etag
andlast-modified
header attributes, the feed attributes, episodes, categories and keywords of the podcast:
public class SuggestedPodcastItemProcessor implements ItemProcessor<SuggestedPodcast, SuggestedPodcast> { private static final int TIMEOUT = 10; @Autowired ReadDao readDao; @Autowired PodcastAndEpisodeAttributesService podcastAndEpisodeAttributesService; @Autowired private PoolingHttpClientConnectionManager poolingHttpClientConnectionManager; @Autowired private SyndFeedService syndFeedService; /** * Method used to build the categories, tags and episodes of the podcast */ @Override public SuggestedPodcast process(SuggestedPodcast item) throws Exception { if(isPodcastAlreadyInTheDirectory(item.getPodcast().getUrl())) { return null; } String[] categories = item.getCategories().trim().split("\\s*,\\s*"); item.getPodcast().setAvailability(org.apache.http.HttpStatus.SC_OK); //set etag and last modified attributes for the podcast setHeaderFieldAttributes(item.getPodcast()); //set the other attributes of the podcast from the feed podcastAndEpisodeAttributesService.setPodcastFeedAttributes(item.getPodcast()); //set the categories List<Category> categoriesByNames = readDao.findCategoriesByNames(categories); item.getPodcast().setCategories(categoriesByNames); //set the tags setTagsForPodcast(item); //build the episodes setEpisodesForPodcast(item.getPodcast()); return item; } ...... }
the processor from the second job uses the ‘Driving Query’ approach, where I expand the data retrieved from the Reader with another “JPA-read” and I group the items on podcasts with episodes so that it looks nice in the emails that I am sending out to subscribers:
@Scope("step") public class NotifySubscribersItemProcessor implements ItemProcessor<User, User> { @Autowired EntityManager em; @Value("#{jobParameters[updateFrequency]}") String updateFrequency; @Override public User process(User item) throws Exception { String sqlInnerJoinEpisodes = "select e from User u JOIN u.podcasts p JOIN p.episodes e WHERE u.email=?1 AND p.updateFrequency=?2 AND" + " e.isNew IS NOT NULL AND e.availability=200 ORDER BY e.podcast.podcastId ASC, e.publicationDate ASC"; TypedQuery<Episode> queryInnerJoinepisodes = em.createQuery(sqlInnerJoinEpisodes, Episode.class); queryInnerJoinepisodes.setParameter(1, item.getEmail()); queryInnerJoinepisodes.setParameter(2, UpdateFrequency.valueOf(updateFrequency)); List<Episode> newEpisodes = queryInnerJoinepisodes.getResultList(); return regroupPodcastsWithEpisodes(item, newEpisodes); } ....... }
Note:
If you’d like to find out more how to use the Apache Http Client, to get theetag
andlast-modified
headers, you can have a look at my post – How to use the new Apache Http Client to make a HEAD request
6. Execute the batch application
Batch processing can be embedded in web applications and WAR files, but I chose in the beginning the simpler approach that creates a standalone application, that can be started by the Java main()
method:
package org.podcastpedia.batch; //imports ...; @ComponentScan @EnableAutoConfiguration public class Application { private static final String NEW_EPISODES_NOTIFICATION_JOB = "newEpisodesNotificationJob"; private static final String ADD_NEW_PODCAST_JOB = "addNewPodcastJob"; public static void main(String[] args) throws BeansException, JobExecutionAlreadyRunningException, JobRestartException, JobInstanceAlreadyCompleteException, JobParametersInvalidException, InterruptedException { Log log = LogFactory.getLog(Application.class); SpringApplication app = new SpringApplication(Application.class); app.setWebEnvironment(false); ConfigurableApplicationContext ctx= app.run(args); JobLauncher jobLauncher = ctx.getBean(JobLauncher.class); if(ADD_NEW_PODCAST_JOB.equals(args[0])){ //addNewPodcastJob Job addNewPodcastJob = ctx.getBean(ADD_NEW_PODCAST_JOB, Job.class); JobParameters jobParameters = new JobParametersBuilder() .addDate("date", new Date()) .toJobParameters(); JobExecution jobExecution = jobLauncher.run(addNewPodcastJob, jobParameters); BatchStatus batchStatus = jobExecution.getStatus(); while(batchStatus.isRunning()){ log.info("*********** Still running.... **************"); Thread.sleep(1000); } log.info(String.format("*********** Exit status: %s", jobExecution.getExitStatus().getExitCode())); JobInstance jobInstance = jobExecution.getJobInstance(); log.info(String.format("********* Name of the job %s", jobInstance.getJobName())); log.info(String.format("*********** job instance Id: %d", jobInstance.getId())); System.exit(0); } else if(NEW_EPISODES_NOTIFICATION_JOB.equals(args[0])){ JobParameters jobParameters = new JobParametersBuilder() .addDate("date", new Date()) .addString("updateFrequency", args[1]) .toJobParameters(); jobLauncher.run(ctx.getBean(NEW_EPISODES_NOTIFICATION_JOB, Job.class), jobParameters); } else { throw new IllegalArgumentException("Please provide a valid Job name as first application parameter"); } System.exit(0); } }
The best explanation for SpringApplication
-, @ComponentScan
- and @EnableAutoConfiguration
-magic you get from the source – Getting Started – Creating a Batch Service:
“The main()
method defers to the SpringApplication
helper class, providing Application.class
as an argument to its run()
method. This tells Spring to read the annotation metadata from Application
and to manage it as a component in the Spring application context.
The @ComponentScan
annotation tells Spring to search recursively through theorg.podcastpedia.batch
package and its children for classes marked directly or indirectly with Spring’s @Component
annotation. This directive ensures that Spring finds and registers BatchConfiguration
, because it is marked with @Configuration
, which in turn is a kind of @Component
annotation.
The @EnableAutoConfiguration
annotation switches on reasonable default behaviors based on the content of your classpath. For example, it looks for any class that implements the CommandLineRunner
interface and invokes its run()
method.”
Execution construction steps:
- the
JobLauncher
, which is a simple interface for controlling jobs, is retrieved from the ApplicationContext. Remember this is automatically made available via the@EnableBatchProcessing
annotation. - now based on the first parameter of the application (
args[0]
), I will retrieve the correspondingJob
from theApplicationContext
- then the
JobParameters
are prepared, where I use the current date -.addDate("date", new Date())
, so that the job executions are always unique. - once everything is in place, the job can be executed:
JobExecution jobExecution = jobLauncher.run(addNewPodcastJob, jobParameters);
- you can use the returned
jobExecution
to gain access toBatchStatus
, exit code, or job name and id.
Note: I highly recommend you read and understand the Meta-Data Schema for Spring Batch. It will also help you better understand the Spring Batch Domain objects.
6.1. Running the application on dev and prod environments
To be able to run the Spring Batch / Spring Boot application on different environments I make use of the Spring Profiles capability. By default the application runs with development data (database). But if I want the job to use the production database I have to do the following:
- provide the following environment argument
-Dspring.profiles.active=prod
- have the production database properties configured in the
application-prod.properties
file in the classpath, right besides the defaultapplication.properties
file
Summary
In this tutorial we’ve learned how to configure a Spring Batch project with Spring Boot and Java configuration, how to use some of the most common readers in batch processing, how to configure some simple jobs, and how to start Spring Batch jobs from a main method.
Note:
As I mentioned, I am fairly new to Spring Batch, and especially to Spring Boot and Spring Configuration with Java, so if you see any potential for improvement (code, job design etc.) please make a pull request or leave a comment below. Thanks a lot.
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