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# Exception Interceptor

This interceptor forms the core functionality of the exception handling feature. Exception handling allows you to map an exception to a result code, just as if the action returned a result code instead of throwing an unexpected exception. When an exception is encountered, it is wrapped with an `ExceptionHolder` and pushed on the stack, providing easy access to the exception from within your result.

> Note: While you can configure exception mapping in your configuration file at any point, the configuration will not have any effect if this interceptor is not in the interceptor stack for your actions. It is recommended that you make this interceptor the first interceptor on the stack, ensuring that it has full access to catch any exception, even those caused by other interceptors.

## Parameters

- `logEnabled` (optional) - should exceptions also be logged? (boolean true | false)

- `logLevel` (optional) - what log level should we use (`trace, debug, info, warn, error, fatal`)? - default is `debug`
- `logCategory` (optional) - if provided we would use this category (eg. `com.mycompany.app`). Default is to use `com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor`.

The parameters above enables us to log all thrown exceptions with stacktrace in our own logfile, and present a friendly webpage (with no stacktrace) to the end user.

## Extending the Interceptor

If you want to add custom handling for publishing the Exception, you may override `#publishException(com.opensymphony.xwork2.ActionInvocation, ExceptionHolder)`. The default implementation pushes the given `ExceptionHolder` on a value stack. A custom implementation could add additional logging etc.

## Examples

     <struts>
         <package name="default" extends="xwork-default">
             <global-results>
                 <result name="error" type="freemarker">error.ftl</result>
             </global-results>

             <global-exception-mappings>
                 <exception-mapping exception="java.lang.Exception" result="error"/>
             </global-exception-mappings>

             <action name="test">
                 <interceptor-ref name="exception"/>
                 <interceptor-ref name="basicStack"/>
                 <exception-mapping exception="com.acme.CustomException" result="custom_error"/>
                 <result name="custom_error">custom_error.ftl</result>
                 <result name="success" type="freemarker">test.ftl</result>
             </action>
         </package>
     </struts>