Using a Java Servlet Filter to intercept the response HTTP status code with NetBeans IDE 7 and Maven
Join the DZone community and get the full member experience.
Join For FreeVersion 2.3 of the Java servlet spec introduced the concept of filters. According to the documentation from Oracle’s site: “A filter dynamically intercepts requests and responses to transform or use the information contained in the requests or responses”. Today I’ll show you how to build a simple filter to intercept the response HTTP response code using annotations introduced in the Servlet 3.0 specification.
With NetBeans IDE 7 create a new Maven Java Web Application called: Intercept
Delete the index.jsp file under the Web Pages folder. Right-click on the project and add a new servlet called: MainServlet
Since we are using the new Servlet 3 annotations we don’t need to set a whole lot of properties.
Maven generates a decent MainServlet.java file for us, I just removed the comments for the output. My file looks like this:
package com.giantflyingsaucer.intercept;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "MainServlet", urlPatterns = {"/"})
public class MainServlet extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet MainServlet</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Servlet MainServlet</h1>");
out.println("</body>");
out.println("</html>");
} finally {
out.close();
}
}
// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
* Handles the HTTP <code>GET</code> method.
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Handles the HTTP <code>POST</code> method.
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Returns a short description of the servlet.
* @return a String containing servlet description
*/
@Override
public String getServletInfo() {
return "Short description";
}// </editor-fold>
}
Right-click on the project and add a Filter called: InterceptFilter
We will add the following two lines to the doFilter method.
HttpServletResponse hsr = (HttpServletResponse) response;
System.out.println("HTTP Status: " + hsr.getStatus());
My doFilter method looks like this:
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)
throws IOException, ServletException {
if (debug) {
log("InterceptFilter:doFilter()");
}
doBeforeProcessing(request, response);
HttpServletResponse hsr = (HttpServletResponse) response;
System.out.println("HTTP Status: " + hsr.getStatus());
Throwable problem = null;
try {
chain.doFilter(request, response);
} catch (Throwable t) {
problem = t;
t.printStackTrace();
}
doAfterProcessing(request, response);
if (problem != null) {
if (problem instanceof ServletException) {
throw (ServletException) problem;
}
if (problem instanceof IOException) {
throw (IOException) problem;
}
sendProcessingError(problem, response);
}
}
Clean and Build the project and deploy it to Apache Tomcat. Access the URL with a browser and take a look at your catalina.out file and you should see the HTTP response code.
Note: You shouldn’t need to do any changes to the web.xml file for this project to work.
Opinions expressed by DZone contributors are their own.
Comments