The default Interceptor stack is designed to serve the needs of most applications. Most applications will not need to add Interceptors or change the Interceptor stack.

Many Actions share common concerns. Some Actions need input validated. Other Actions may need a file upload to be pre-processed. Another Action might need protection from a double submit. Many Actions need drop-down lists and other controls pre-populated before the page displays.

The framework makes it easy to share solutions to these concerns using an "Interceptor" strategy. When you request a resource that maps to an "action", the framework invokes the Action object. But, before the Action is executed, the invocation can be intercepted by another object. After the Action executes, the invocation could be intercepted again. Unsurprisingly, we call these objects "Interceptors."


Understanding Interceptors

Interceptors can execute code before and after an Action is invoked. Most of the framework's core functionality is implemented as Interceptors. Features like double-submit guards, type conversion, object population, validation, file upload, page preparation, and more, are all implemented with the help of Interceptors. Each and every Interceptor is pluggable, so you can decide exactly which features an Action needs to support.

Interceptors can be configured on a per-action basis. Your own custom Interceptors can be mixed-and-matched with the Interceptors bundled with the framework. Interceptors "set the stage" for the Action classes, doing much of the "heavy lifting" before the Action executes.

Action Lifecyle

In some cases, an Interceptor might keep an Action from firing, because of a double-submit or because validation failed. Interceptors can also change the state of an Action before it executes.

The Interceptors are defined in a stack that specifies the execution order. In some cases, the order of the Interceptors on the stack can be very important.

Configuring Interceptors

xmlstruts.xml<package name="default" extends="struts-default"> <interceptors> <interceptor name="timer" class=".."/> <interceptor name="logger" class=".."/> </interceptors> <action name="login" class="tutorial.Login"> <interceptor-ref name="timer"/> <interceptor-ref name="logger"/> <result name="input">login.jsp</result> <result name="success" type="redirectAction">/secure/home</result> </action> </package>

Stacking Interceptors

With most web applications, we find ourselves wanting to apply the same set of Interceptors over and over again. Rather than reiterate the same list of Interceptors, we can bundle these Interceptors together using an Interceptor Stack.

xmlstruts.xml<package name="default" extends="struts-default"> <interceptors> <interceptor name="timer" class=".."/> <interceptor name="logger" class=".."/> <interceptor-stack name="myStack"> <interceptor-ref name="timer"/> <interceptor-ref name="logger"/> </interceptor-stack> </interceptors> <action name="login" class="tutuorial.Login"> <interceptor-ref name="myStack"/> <result name="input">login.jsp</result> <result name="success" type="redirectAction">/secure/home</result> </action> </package>

Looking inside struts-default.xml, we can see how it's done.

The Default Configuration

{snippet:id=all|lang=xml|url=struts2/core/src/main/resources/struts-default.xml}Since the struts-default.xml is included in the application's configuration by default, all of the predefined interceptors and stacks are available "out of the box".

Framework Interceptors

Interceptor classes are also defined using a key-value pair specified in the Struts configuration file. The names specified below come specified in struts-default.xml. If you extend the struts-default package, then you can use the names below. Otherwise, they must be defined in your package with a name-class pair specified in the <interceptors> tag.




Alias Interceptor


Converts similar parameters that may be named differently between requests.

Chaining Interceptor


Makes the previous Action's properties available to the current Action. Commonly used together with <result type="chain"> (in the previous Action).

Checkbox Interceptor


Adds automatic checkbox handling code that detect an unchecked checkbox and add it as a parameter with a default (usually 'false') value. Uses a specially named hidden field to detect unsubmitted checkboxes. The default unchecked value is overridable for non-boolean value'd checkboxes.

Cookie Interceptor


Inject cookie with a certain configurable name / value into action. (Since 2.0.7.)

CookieProvider Interceptor


Transfer cookies from action to response (Since 2.3.15.)

Conversion Error Interceptor


Adds conversion errors from the ActionContext to the Action's field errors

Create Session Interceptor


Create an HttpSession automatically, useful with certain Interceptors that require a HttpSession to work properly (like the TokenInterceptor)



Provides several different debugging screens to provide insight into the data behind the page.

Execute and Wait Interceptor


Executes the Action in the background and then sends the user off to an intermediate waiting page.

Exception Interceptor


Maps exceptions to a result.

File Upload Interceptor


An Interceptor that adds easy access to file upload support.

I18n Interceptor


Remembers the locale selected for a user's session.

Logger Interceptor


Outputs the name of the Action.

Message Store Interceptor


Store and retrieve action messages / errors / field errors for action that implements ValidationAware interface into session.

Model Driven Interceptor


If the Action implements ModelDriven, pushes the getModel Result onto the Value Stack.

Scoped Model Driven Interceptor


If the Action implements ScopedModelDriven, the interceptor retrieves and stores the model from a scope and sets it on the action calling setModel.

Parameters Interceptor


Sets the request parameters onto the Action.

Prepare Interceptor


If the Action implements Preparable, calls its prepare method.

Scope Interceptor


Simple mechanism for storing Action state in the session or application scope.

Servlet Config Interceptor


Provide access to Maps representing HttpServletRequest and HttpServletResponse.

Static Parameters Interceptor


Sets the struts.xml defined parameters onto the action. These are the <param> tags that are direct children of the <action> tag.

Roles Interceptor


Action will only be executed if the user has the correct JAAS role.

Timer Interceptor


Outputs how long the Action takes to execute (including nested Interceptors and View)

Token Interceptor


Checks for valid token presence in Action, prevents duplicate form submission.

Token Session Interceptor


Same as Token Interceptor, but stores the submitted data in session when handed an invalid token

Validation Interceptor


Performs validation using the validators defined in action-validation.xml

Default Workflow Interceptor


Calls the validate method in your Action class. If Action errors are created then it returns the INPUT view.

Parameter Filter Interceptor


Removes parameters from the list of those available to Actions

Profiling Interceptor


Activate profiling through parameter

Multiselect Interceptor


Like the checkbox interceptor detects that no value was selected for a field with multiple values (like a select) and adds an empty parameter

NoOp InterceptornoopDoes nothing, just passes invocation further, used in empty stack

Since 2.0.7, Interceptors and Results with hyphenated names were converted to camelCase. (The former model-driven is now modelDriven.) The original hyphenated names are retained as "aliases" until Struts 2.1.0. For clarity, the hyphenated versions are not listed here, but might be referenced in prior versions of the documentation.

Method Filtering


Interceptor Parameter Overriding

Interceptor's parameter could be overridden through the following ways :

Method 1:

xml<action name="myAction" class="myActionClass"> <interceptor-ref name="exception"/> <interceptor-ref name="alias"/> <interceptor-ref name="params"/> <interceptor-ref name="servletConfig"/> <interceptor-ref name="prepare"/> <interceptor-ref name="i18n"/> <interceptor-ref name="chain"/> <interceptor-ref name="modelDriven"/> <interceptor-ref name="fileUpload"/> <interceptor-ref name="staticParams"/> <interceptor-ref name="params"/> <interceptor-ref name="conversionError"/> <interceptor-ref name="validation"> <param name="excludeMethods">myValidationExcudeMethod</param> </interceptor-ref> <interceptor-ref name="workflow"> <param name="excludeMethods">myWorkflowExcludeMethod</param> </interceptor-ref> </action>

Method 2:

xml<action name="myAction" class="myActionClass"> <interceptor-ref name="defaultStack"> <param name="validation.excludeMethods">myValidationExcludeMethod</param> <param name="workflow.excludeMethods">myWorkflowExcludeMethod</param> </interceptor-ref> </action>

In the first method, the whole default stack is copied and the parameter then changed accordingly.

In the second method, the interceptor-ref refers to an existing interceptor-stack, namely defaultStack in this example, and override the validator and workflow interceptor excludeMethods attribute. Note that in the param tag, the name attribute contains a dot (.) the word before the dot(.) specifies the interceptor name whose parameter is to be overridden and the word after the dot (.) specifies the parameter itself. The syntax is as follows:


Note also that in this case the interceptor-ref name attribute is used to indicate an interceptor stack which makes sense as if it is referring to the interceptor itself it would be just using Method 1 describe above.

Method 3:

xml<interceptors> <interceptor-stack name="parentStack"> <interceptor-ref name="defaultStack"> <param name="params.excludeParams">token</param> </interceptor-ref> </interceptor-stack> </interceptors> <default-interceptor-ref name="parentStack"/>

Interceptor Parameter Overriding Inheritance

Parameters override are not inherited in interceptors, meaning that the last set of overridden parameters will be used. For example, if a stack overrides the parameter "defaultBlock" for the "postPrepareParameterFilter" interceptor as:

xml<interceptor-stack name="parentStack"> <interceptor-ref name="postPrepareParameterFilter"> <param name="defaultBlock">true</param> </interceptor-ref> </interceptor-stack>

and an action overrides the "allowed" for "postPrepareParameterFilter":

xml<package name="child2" namespace="/child" extends="parentPackage"> <action name="list" class="SomeAction"> <interceptor-ref name="parentStack"> <param name="postPrepareParameterFilter.allowed"></param> </interceptor-ref> </action> </package>

Then, only "allowed" will be overridden for the "postPrepareParameterFilter" interceptor in that action, the other params will be null.

Lazy parameters

This functionality was added in Struts 2.5.9

It is possible to define an interceptor with parameters evaluated during action invocation. In such case the interceptor must be marked with WithLazyParams interface. This must be developer's decision as interceptor must be aware of having those parameters set during invocation and not when the interceptor is created as it happens in normal way.

Params are evaluated as any other expression starting with from action as a top object.

xml<action name="LazyFoo" class="com.opensymphony.xwork2.SimpleAction"> <result name="success">result.jsp</result> <interceptor-ref name="lazy"> <param name="foo">${bar}</param> </interceptor-ref> </action>javapublic class MockLazyInterceptor extends AbstractInterceptor implements WithLazyParams { private String foo = ""; public void setFoo(String foo) { = foo; } public String intercept(ActionInvocation invocation) throws Exception { .... return invocation.invoke(); } }

Please be aware that order of interceptors can matter when want to access parameters passed via request as those parameters are set by Parameters Interceptor.

Order of Interceptor Execution

Interceptors provide an excellent means to wrap before/after processing. The concept reduces code duplication (think AOP).

xml<interceptor-stack name="xaStack"> <interceptor-ref name="thisWillRunFirstInterceptor"/> <interceptor-ref name="thisWillRunNextInterceptor"/> <interceptor-ref name="followedByThisInterceptor"/> <interceptor-ref name="thisWillRunLastInterceptor"/> </interceptor-stack>

(warning) Note that some Interceptors will interrupt the stack/chain/flow ... so the order is very important.

Interceptors implementing com.opensymphony.xwork2.interceptor.PreResultListener will run after the Action executes but before the Result executes.

thisWillRunFirstInterceptor thisWillRunNextInterceptor followedByThisInterceptor thisWillRunLastInterceptor MyAction1 MyAction2 (chain) MyPreResultListener MyResult (result) thisWillRunLastInterceptor followedByThisInterceptor thisWillRunNextInterceptor thisWillRunFirstInterceptor


Next: Writing Interceptors


  1. TODO: Review list of Interceptors against latest distribution.

  2. TODO: Update image to indicate DispatchFilter

  3. The section "The Default Configuration" should be updated to reflect the contents of the current struts-default.xml which is different (TODO hasn't been done for 9 months).

    Under "Checkbox Interceptor", a strang paragraph "Minor source formatting and cleaned out an empty directory" is present.

    The sentence "An abstract Interceptor that is applied to selectively according to specified included/excluded method lists." is meaningless.