Using a Java Servlet Filter to intercept the response HTTP status code with NetBeans IDE 7 and Maven
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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.
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