Debugging Servlets using Netbeans

It is possible to execute and debug servlets from within NetBeans. This is done by using the internal Tomcat server that comes with NetBeans. In order to allow unregistered servlets to run, you should modify web.xml and server.xml in the conf directory.

• Which conf is mine?
• Declaring the Invoker Servlet and Enabling Servlet Mapping
• Mount the Directory where you want a context
• Add a context
• Try to Debug
• No web modules in repository

Which conf directory is mine?

In NetBeans, Tomcat is set up in a multi-user format. Your conf, logs, and webapps directories are located under
C:\Documents and Settings\your userid\.netbeans\3.6\jakarta-tomcat-5.0.19_base

This is the location of the conf directory where you will find the web.xml and server.xml files for your deployment of Tomcat.

Declaring the Invoker Servlet and Enabling Servlet Mapping

I recommend that you declare the Invoker Servlet in the web.xml file that is located in the conf directory. The following code should be placed after the servlet tags for the default servlet.

   <servlet>
      <servlet-name>invoker</servlet-name>
      <servlet-class>org.apache.catalina.servlets.InvokerServlet</servlet-class>
      <init-param>
        <param-name>debug</param-name>
        <param-value>0</param-value>
      </init-param>
      <load-on-startup>2</load-on-startup>
   </servlet>

I also recommend that you enable servlet mapping throughout your deployment. Add the following code where all the other servlet mappings are located in the web.xml file. Place this after the servlet mapping for the default servlet.

  <servlet-mapping>
    <servlet-name>invoker</servlet-name>
    <url-pattern>/servlet/*</url-pattern>
  </servlet-mapping>

Mount the directory where you want a context.

Create a context and mount this file system in NetBeans.

• File
• Mount File System
• Local Directory
• Browse to the directory for the context. This will be the directory that will contain WEB-INF/classes.

Add a Context

Add the context to the internal Tomcat of NetBeans

• Open the Explorer window in NetBeans (from the View menu)
• Click on the Runtime tab
• Open the Server Registry entry
• Click on Installed Servers
• Click on Tomcat 4.0. If it doesn't open, then right click and click Explore From Here
• Click on Internal
• Right click on localhost and select Add Context
• Select the directory that you just mounted. You can also specify the name to be used in the URL.

Be sure that the context is reloadable

• In the Explorer, right click on Internal
• Select Configure (edit server.xml)
• Find the new context and be sure to add
  reloadable="true"

Try to Debug a file

When you execute a servlet in NetBeans, it will try to start the internal Tomcat. Since Tomcat is running inside of NetBeans, you will be able to set breakpoints in the code and stop execution of the servlet. You will still use the browser to interact with the servlet, but control will return to NetBeans when a breakpoint is encountered.

• Create a servlet in the classes directory of the new context.
  • If you use the Servlet Template to create your servlet, then NetBeans already knows that it is a servlet.
  • If you create a servlet from scratch, or copy a servlet into the web module, then do the following
    • In the Explorer, open the Project Default view
    • Naviagate to the classes folder in the web module.
    • Right-click on your servlet's name
    • Select the Tools submenu
    • Select Mark As Servlet (if the pop up menu only has Cancel Servlet then NetBeans already knows it is a servlet)
    • A new window will appear within a few seconds. It is recommending changes for the web.xml file. If you do not have initialization parameters, then you can just select Close. If you select Process or Process All, then NetBeans will place some generic tags in the web.xml file of the web module. You will need to edit the web.xml file to complete the tags with specific information about your servlet.
• Place a breakpoint on a line inside of doGet
• Compile your .java file in NetBeans.
• From the Debug menu select Start Session and Run In Debugger
• NetBeans will start the internal Tomcat and will display the servlet in the browser.
• Control should pass to the breakpoint in NetBeans.

No web modules in repository

If you get the error

No web modules in repository

then you did not add the context correctly. See the instructions on Mounting a File System and Adding a Context.