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README.adoc
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README.adoc

servlet-filterlistener: How to Write Servlet Filters and Listeners

The servlet-filterlistener quickstart demonstrates how to use Servlet filters and listeners in an application.

What is it?

The servlet-filterlistener quickstart demonstrates how to use Servlet filters and listeners in {productNameFull}.

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.

Access the Application

The application will be running at the following URL http://localhost:8080/{artifactId}/.

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