The example code for this tutorial, debugging_struts, is available for checkout at https://github.com/apache/struts-examples.
During development of a Struts 2 web application you may want to view the information being managed by the Struts 2 framework. This tutorial will cover two tools you can use to see how Struts 2 views your web application. One tool is the Struts 2 configuration plugin and the other is the debugging interceptor. This article also discusses how to set the log level to see more or fewer log messages.
The Struts 2 user mailing list is an excellent place to get help. If you are having a problem getting the tutorial example applications to work search the Struts 2 mailing list. If you don't find an answer to your problem, post a question on the mailing list.
The Struts 2 config browser plugin provides details about the configuration the Struts 2 framework is using to run your application. To use the plugin your application needs to have the struts2-config-browser-plugin-x.x.x.x.jar in your application's class path. The config-browser-plugin jar is part of the Struts 2 download and is also available in the Maven repository.
To use the plugin in your application, just call index.action in namespace config-browser. For example you could have the following link on your admin page (or just anywhere during your development).
In the example application, there is a link to the configuration browser on the index.jsp page.
Clicking on the link for the configuration browser will cause the Struts 2 framework to return this page to your browser.
You can click on an action link to see the configuration for that action. For example clicking on the register action link results in this.
You may then click on one of the tabs (Results, Exception Mappings, Interceptors, Properties, Validators) to get more information about how the Struts 2 framework is has configured that specific action.
On the left side of the page is the config browser plugin menu. Clicking on constants will render a view that lists all the Struts 2 constants and their properties for your application. Clicking on beans shows the beans Struts 2 is managing. Clicking on Jars shows the jars your application is using.
Using the Debugging Interceptor
If you have set
devMode to true (in the example application see struts.xml) then one of the interceptors that is activated when Struts 2 processes an action is the DebuggingInterceptor. The DebuggingInterceptor looks for a query string appended to the action URL with a name of debug and a value of xml, console, command, or browser.
If the DebuggingInterceptor finds that query string then it will halt further execution of the action and instead return to the browser debugging information. The format of the returned information depends on the value of the debug query parameter. See DebuggingInterceptor for more detail.
In the example application on the index.jsp is a link for displaying debugging information. This link includes the query string debug=browser. If you click on this link you'll see a table with columns that can be expanded and collapsed. The table contains the various objects and their state being managed by the Struts 2 framework.
Note that to enable the correct display and interaction of the expand/collapse links on the debugging information web page you need to include the s:head tag in your JSP's head section (see index.jsp in the example application) and also include the Struts 2 dojo plugin in your application's class path. The Struts 2 dojo plugin is available as part of the Struts 2 download and from the Maven repository.
Struts 2 Logging
The Struts 2 framework will write to a log a great deal of information if you've configured the log properties to log at the debug level. In the example application, view log4j.xml. The two major packages involved in the Struts 2 framework, com.opensymphony and org.apache.struts2, are configured to write debug and above log messages. When you run the application view the standard out for your Servlet container to see all the information written to the log. Please check Logging page for other options.
Using the configuration browser plugin and the debugging interceptor can assist you in trouble shooting a problem with a Struts 2 web application. These tools should only be used in development.
Prior to creating your war file for deployment to production you should change devmode to false and remove the debugging links. You may also want to adjust the level of logging in your log properties file to a higher level (info or warn) to reduce the number of log messages.
In our next tutorial we'll cover how to use additional Struts 2 form tags.