Exception Handling

The example code for this tutorial, Exception_Handling_Struts2_Ant or Exception_Handling_Struts2_Mvn, is available on Google Code - http://code.google.com/p/struts2-examples/downloads/list. After downloading and unzipping the file, you'll have a folder named Exception_Handling_Struts2_Ant (or Exception_Handling_Struts2_Mvn). In that folder will be a README.txt file with instructions on now to build and run the example application.

Introduction

In this tutorial we'll explore using how to enable the Struts 2 framework to handle any uncaught exceptions generated by a web application. Struts 2 provides robust exception handling, including the ability to automatically log any uncaught exceptions and redirect the user to a error web page.

The code discussed in this tutorial can be download from Google Code - http://code.google.com/p/struts2-examples/downloads/list.

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.

Global Exception Handling

Using the Struts 2 framework you can specify in the struts.xml how the framework should handle uncaught exceptions. The handling logic can apply to all actions (global exception handling) or to a specific action. Let's first discuss how to enable global exception handling.

To enable global exception handling you need to add two nodes to struts.xml: global-exception-mapping and global-results. For example examine struts.xml from the Exception Handling code download (http://code.google.com/p/struts2-examples/downloads/list).

  
   <global-exception-mappings>
	<exception-mapping exception="org.apache.struts.register.exceptions.SecurityBreachException" result="securityerror" />
	 <exception-mapping exception="java.lang.Exception" result="error" />
   </global-exception-mappings>
 
  <global-results>
        <result name="securityerror">/securityerror.jsp</result>
  	<result name="error">/error.jsp</result>
   </global-results>

The global exception mapping node tells the Struts 2 framework what to do if an uncaught exception of the type specified (or a child of that type) is thrown by application. For example if a SecurityBreachException is thrown but not caught, the Struts 2 Action class will return a result of "securityerror". All other uncaught exceptions will cause the Struts 2 Action class to return a result of "error".

The global results mapping node relates the result value to a specific view page. For example the result "securityerror" will cause the framework to redirect the user's browser to the securityerror.jsp view page.