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servlet-filterlistener: How to Write Servlet Filters and Listeners

Author: Jonathan Fuerth
Level: Intermediate
Technologies: Servlet Filter, Servlet Listener
Summary: The servlet-filterlistener quickstart demonstrates how to use Servlet filters and listeners in an application.
Target Product: JBoss EAP
Source: https://github.com/jboss-developer/jboss-eap-quickstarts/

What is it?

The servlet-filterlistener quickstart demonstrates how to use Servlet filters and listeners in Red Hat JBoss Enterprise Application Platform.

This example contains the following classes:

  • FilterExampleServlet: A simple servlet that prints a form that contains an input field and a Send button.
  • VowelRemoverFilter: A servlet filter that removes the vowels from the text entered in the form.
  • ParameterDumpingRequestListener: A simple servlet request listener that creates a map of the original HTTP request parameter values before the filter is applied.

System Requirements

The application this project produces is designed to be run on Red Hat JBoss Enterprise Application Platform 7.1 or later.

All you need to build this project is Java 8.0 (Java SDK 1.8) or later and Maven 3.3.1 or later. See Configure Maven for JBoss EAP 7.1 to make sure you are configured correctly for testing the quickstarts.

Use of EAP7_HOME

In the following instructions, replace EAP7_HOME with the actual path to your JBoss EAP installation. The installation path is described in detail here: Use of EAP7_HOME and JBOSS_HOME Variables.

Start the Server

  1. Open a command prompt and navigate to the root of the JBoss EAP directory.

  2. The following shows the command line to start the server:

     For Linux:   EAP7_HOME/bin/standalone.sh
 For Windows: EAP7_HOME\bin\standalone.bat

Build and Deploy the Quickstart

  1. Make sure you have started the JBoss EAP server as described above.

  2. Open a command prompt and navigate to the root directory of this quickstart.

  3. Type this command to build and deploy the archive:

     mvn clean install wildfly:deploy

  4. This will deploy target/servlet-filterlistener.war to the running instance of the server.

Access the Application

The application will be running at the following URL http://localhost:8080/servlet-filterlistener/.

You are presented with a form containing an input field and a Send button. To test the quickstart:

  1. Enter some text in the field, for example:

     This is only a test!

  2. Click Send.

  3. The servlet filter intercepts and removes the vowels from the text entered in the form and displays:

     You Typed: Ths s nly tst!

  4. The server console displays the following log messages.

    The following messages appear in the log when you access the application URL. This is because the ParameterDumpingRequestListener, which is a ServletRequestListener, and the VowelRemoverFilter both map to the application context and print logs for every request. Note that the VowelRemoveFilter contains logic to handle empty input field arguments.

     INFO  [io.undertow.servlet] (default task-46) ParameterDumpingRequestListener: request has been initialized. It has 0 parameters:
 INFO  [io.undertow.servlet] (default task-46) VowelRemoverFilter initialized
 INFO  [io.undertow.servlet] (default task-46) VowelRemoverFilter invoking filter chain...
 INFO  [io.undertow.servlet] (default task-46) VowelRemoverFilter done filtering request
 INFO  [io.undertow.servlet] (default task-46) ParameterDumpingRequestListener: request has been destroyed
 INFO  [io.undertow.servlet] (default task-48) ParameterDumpingRequestListener: request has been initialized. It has 0 parameters:
 INFO  [io.undertow.servlet] (default task-48) VowelRemoverFilter invoking filter chain...
 INFO  [io.undertow.servlet] (default task-48) VowelRemoverFilter done filtering request
 INFO  [io.undertow.servlet] (default task-48) ParameterDumpingRequestListener: request has been destroyed

    The following messages appear in the log when you type "This is only a test!" in the input field and click Send.

     INFO  [io.undertow.servlet] (default task-50) ParameterDumpingRequestListener: request has been initialized. It has 1 parameters:
 INFO  [io.undertow.servlet] (default task-50)   userInput=This is only a test!
 INFO  [io.undertow.servlet] (default task-50) VowelRemoverFilter invoking filter chain...
 INFO  [io.undertow.servlet] (default task-50) VowelRemoverFilter done filtering request
 INFO  [io.undertow.servlet] (default task-50) ParameterDumpingRequestListener: request has been destroyed

Undeploy the Archive

  1. Make sure you have started the JBoss EAP server as described above.

  2. Open a command prompt and navigate to the root directory of this quickstart.

  3. When you are finished testing, type this command to undeploy the archive:

     mvn wildfly:undeploy

Run the Quickstart in Red Hat JBoss Developer Studio or Eclipse

You can also start the server and deploy the quickstarts or run the Arquillian tests from Eclipse using JBoss tools. For general information about how to import a quickstart, add a JBoss EAP server, and build and deploy a quickstart, see Use JBoss Developer Studio or Eclipse to Run the Quickstarts.

Debug the Application

If you want to debug the source code of any library in the project, run the following command to pull the source into your local repository. The IDE should then detect it.

    mvn dependency:sources