[Interceptors can execute code before and after an Action is invoked. Most of the framework's core features are implemented as Interceptors. Object population and type conversion, validation, file uploads, double-submit guards, component setup, and more, are all implemented with Interceptors.

Interceptors can be configured on a per-action basis. 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. The Interceptor strategy promotes reusability and simplicity.

When you access request an "action" URI, the framework invokes the Action object. But, before the Action is executed,

Info

title	TODO

Update the info about the new interceptors

Interceptors

Interceptors allow arbitrary code to be included in the call stack for your action before and/or after processing the action, which can vastly simplify your code itself and provide excellent opportunities for code reuse. Many of the features of XWork and WebWork are implemented as interceptors and can be applied via external configuration along with your own Interceptors in whatever order you specify for any set of actions you define.

In other words, when you access a *.action URL, WebWork's ServletDispatcher proceeds to the invocation of the an action object. Before it is executed, however, the invocation can be intercepted by another object. (Hence the name.) After the Action executes, the invocation can be intercepted again.

Action Lifecyle
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Interceptors can interrupt the request processing, that is hence called interceptor. To have an interceptor executed before (or after) a given action,

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Note

title	Be Careful

Note that some interceptors will interrupt the stack/chain/flow... so the order is very important.

Interceptor configuration:

so that the Action never executes. 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

Code Block

	xml
	xml
title	action.

Code Block

xml

<package name="default" extends="webworkaction-default">
   <interceptors>
       <interceptor name="timer" class=".."/>
       <interceptor name="logger" class=".."/>
   </interceptors>

   <action name="login"
      class="org.hibernate.auction.web.actions.users.tutorial.Login">
        <interceptor-ref name="timer"/>
        <interceptor-ref name="logger"/>
         <result name="input">login.jsp</result>
         <result name="success"
            type="redirect-action">/secure/dashboard.action<home</result>
   </action>
</package>

...

Stacking Interceptors

With most web applications, you'll find yourself wanting to apply the same set of interceptors over and over again. Rather than declare numerous interceptor-refs for each action, you can bundle these interceptors together using an interceptor stack.

Code Block

	xml
	xml
title	action.xml

<package name="default" extends="webworkaction-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="org.hibernate.auction.web.actions.users.tutuorial.Login">
         <interceptor-ref name="myStack"/>
         <result name="input">login.jsp</result>
         <result name="success"
             type="redirect-action">/secure/dashboard.action<home</result>
</action>
</package>

...

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

...

`action-default.xml`

...

Code Block

	xml
	xml
title	action.xml

<!DOCTYPE xwork PUBLIC "-//OpenSymphony Group//XWork 1.0//EN" "http://www.opensymphony.com/xwork/xwork-1.1.dtd">

<!-- // START SNIPPET: webwork-default -->
<xwork>
    <package name="webworkaction-default">
        <result-types>
            <result-type name="chain" class="com.opensymphony.xwork.ActionChainResult"/>
            <result-type name="dispatcher" class="comorg.apache.opensymphonystruts.webworkaction2.dispatcher.ServletDispatcherResult"
                         default="true"/>
            <result-type name="freemarker" class="comorg.apache.opensymphonystruts.webworkaction2.views.freemarker.FreemarkerResult"/>
            <result-type name="httpheader" class="comorg.apache.opensymphonystruts.webworkaction2.dispatcher.HttpHeaderResult"/>
            <result-type name="jasper" class="comorg.apache.opensymphonystruts.webworkaction2.views.jasperreports.JasperReportsResult"/>
            <result-type name="redirect" class="comorg.apache.opensymphonystruts.webworkaction2.dispatcher.ServletRedirectResult"/>
            <result-type name="redirect-action"
                         class="comorg.apache.opensymphonystruts.webworkaction2.dispatcher.ServletActionRedirectResult"/>
            <result-type name="stream" class="comorg.apache.opensymphonystruts.webworkaction2.dispatcher.StreamResult"/>
            <result-type name="velocity" class="comorg.apache.opensymphonystruts.webworkaction2.dispatcher.VelocityResult"/>
            <result-type name="xslt" class="comorg.apache.opensymphonystruts.webworkaction2.views.xslt.XSLTResult"/>
        </result-types>

        <interceptors>
            <interceptor name="alias" class="com.opensymphony.xwork.interceptor.AliasInterceptor"/>
            <interceptor name="autowiring"
                         class="com.opensymphony.xwork.spring.interceptor.ActionAutowiringInterceptor"/>
            <interceptor name="chain" class="com.opensymphony.xwork.interceptor.ChainingInterceptor"/>
            <interceptor name="component" class="com.opensymphony.xwork.interceptor.component.ComponentInterceptor"/>
            <interceptor name="conversionError"
                         class="comorg.apache.opensymphonystruts.webworkaction2.interceptor.WebWorkConversionErrorInterceptor"/>
            <interceptor name="external-ref" class="com.opensymphony.xwork.interceptor.ExternalReferencesInterceptor"/>
            <interceptor name="execAndWait" class="comcorg.apache.opensymphonystruts.webworkaction2.interceptor.ExecuteAndWaitInterceptor"/>
            <interceptor name="exception" class="com.opensymphony.xwork.interceptor.ExceptionMappingInterceptor"/>
            <interceptor name="fileUpload" class="com.opensymphony.webwork.interceptor.FileUploadInterceptor"/>
            <interceptor name="i18n" class="com.opensymphony.xwork.interceptor.I18nInterceptor"/>
            <interceptor name="logger" class="com.opensymphony.xwork.interceptor.LoggingInterceptor"/>
            <interceptor name="model-driven" class="com.opensymphony.xwork.interceptor.ModelDrivenInterceptor"/>
            <interceptor name="params" class="com.opensymphony.xwork.interceptor.ParametersInterceptor"/>
            <interceptor name="prepare" class="com.opensymphony.xwork.interceptor.PrepareInterceptor"/>
            <interceptor name="static-params" class="com.opensymphony.xwork.interceptor.StaticParametersInterceptor"/>
            <interceptor name="servlet-config" class="comorg.apache.opensymphonystruts.webworkaction2.interceptor.ServletConfigInterceptor"/>
            <interceptor name="sessionAutowiring"
                         class="comorg.apache.opensymphonystruts.webworkaction2.spring.interceptor.SessionContextAutowiringInterceptor"/>
            <interceptor name="timer" class="com.opensymphony.xwork.interceptor.TimerInterceptor"/>
            <interceptor name="token" class="com.opensymphony.webwork.interceptor.TokenInterceptor"/>
            <interceptor name="token-session"
                         class="com.opensymphony.webwork.interceptor.TokenSessionStoreInterceptor"/>
            <interceptor name="validation" class="com.opensymphony.xwork.validator.ValidationInterceptor"/>
            <interceptor name="workflow" class="com.opensymphony.xwork.interceptor.DefaultWorkflowInterceptor"/>

            <!-- Basic stack -->
            <interceptor-stack name="basicStack">
                <interceptor-ref name="exception"/>
                <interceptor-ref name="servlet-config"/>
                <interceptor-ref name="prepare"/>
                <interceptor-ref name="static-params"/>
                <interceptor-ref name="params"/>
                <interceptor-ref name="conversionError"/>
            </interceptor-stack>

            <!-- Sample validation and workflow stack -->
            <interceptor-stack name="validationWorkflowStack">
                <interceptor-ref name="basicStack"/>
                <interceptor-ref name="validation"/>
                <interceptor-ref name="workflow"/>
            </interceptor-stack>

            <!-- Sample file upload stack -->
            <interceptor-stack name="fileUploadStack">
                <interceptor-ref name="fileUpload"/>
                <interceptor-ref name="basicStack"/>
            </interceptor-stack>

            <!-- Sample WebWork Inversion of Control stack
                 Note: WebWork's IoC is deprecated - please
                 look at alternatives such as Sprint -->
            <interceptor-stack name="componentStack">
                <interceptor-ref name="component"/>
                <interceptor-ref name="basicStack"/>
            </interceptor-stack>

            <!-- Sample model-driven stack  -->
            <interceptor-stack name="modelDrivenStack">
                <interceptor-ref name="model-driven"/>
                <interceptor-ref name="basicStack"/>
            </interceptor-stack>

            <!-- Sample action chaining stack -->
            <interceptor-stack name="chainStack">
                <interceptor-ref name="chain"/>
                <interceptor-ref name="basicStack"/>
            </interceptor-stack>

            <!-- Sample i18n stack -->
            <interceptor-stack name="chainStack">
                <interceptor-ref name="i18n"/>
                <interceptor-ref name="basicStack"/>
            </interceptor-stack>

            <!-- Sample execute and wait stack.
                 Note: execAndWait should always be the *last* interceptor. -->
            <interceptor-stack name="executeAndWaitStack">
                <interceptor-ref name="basicStack"/>
                <interceptor-ref name="execAndWait"/>
            </interceptor-stack>

            <!-- A complete stack with all the common interceptors in place.
                 Generally, this stack should be the one you use, though it
                 may process additional stuff you don't need, which could
                 lead to some performance problems. Also, the ordering can be
                 switched around (ex: if you wish to have your components
                 before prepare() is called, you'd need to move the component
                 interceptor up -->
            <interceptor-stack name="defaultStack">
                <interceptor-ref name="exception"/>
                <interceptor-ref name="alias"/>
                <interceptor-ref name="prepare"/>
                <interceptor-ref name="servlet-config"/>
                <interceptor-ref name="i18n"/>
                <interceptor-ref name="chain"/>
                <interceptor-ref name="model-driven"/>
                <interceptor-ref name="fileUpload"/>
                <interceptor-ref name="static-params"/>
                <interceptor-ref name="params"/>
                <interceptor-ref name="conversionError"/>
                <interceptor-ref name="validation"/>
                <interceptor-ref name="workflow"/>
            </interceptor-stack>

            <!-- The completeStack is here for backwards compatibility for
                 applications that still refer to the defaultStack by the
                 old name -->
            <interceptor-stack name="completeStack">
                <interceptor-ref name="defaultStack"/>
            </interceptor-stack>
        </interceptors>

        <default-interceptor-ref name="defaultStack"/>
    </package>
</xwork>
<!-- // END SNIPPET: webwork-default -->

...

Since we included webworkaction-default.xml in our xworkaction.xml, all the predefined interceptors and stacks above are available for us to use in our actions. Here's what these interceptors do:

timer

...

clocks how long the action (including nested interceptors and view) takes to execute

...

logger

...

logs the action being executed

...

chain

...

makes the previous action's properties available to the current action. Used to make action chaining (reference: Result Types)

...

static-params: sets the parameters defined in xwork.xml onto the action. These are the <param /> tags that are direct children of the <action /> tag

...

params

...

sets the request (POST and GET) parameters onto the action class. We have seen an example of this in TODO

...

*model-driven

...

if the action implements ModelDriven, pushes the getModel() result onto the Value Stack

...

component

...

enables and makes registered components available to the actions. (reference: IoC & Components)

...

token

...

checks for valid token presence in action, prevents duplicate form submission

...

token-session

...

	same as above, but storing the submitted data in session when handed an invalid token;
validation

...

performs validation using the validators defined in {Action}-validation.xml (reference: Validation).

...

workflow

...

calls the validate method in your action class. If action errors created then it returns the INPUT view. Good to use together with the validation interceptor (reference: Validation)

...

servlet-config

...

give access to HttpServletRequest and HttpServletResponse (think twice before using this since this ties you to the Servlet API)

...

prepare

...

allows you to programmatic access to your Action class before the parameters are set on it.

...

conversionError

...

Adds field errors if any type-conversion errors occurred

...

\

execAndWait

...

	Spawns a separate thread to execute the action
fileUpload

...

Sets uploaded files as action files (File objects)

In addition to the prepackaged interceptorsInterceptors, webwork action-default.xml includes prepackaged
combinations of these interceptors in named interceptor stacksInterceptor Stacks.

Building your own Interceptor

If none of the above interceptors suit your particular need, you will have to stock Interceptors meets your needs, you can implement your own interceptorInterceptor. Fortunately, this is an easy task to accomplish. Suppose we need an interceptor Interceptor that places a greeting in the Session session according to the time of the day (morning, afternoon or evening). Here's how we could implement it:

Create an interceptor Interceptor class, which is a class that implements the com.opensymphony.xwork.interceptor.Interceptor interface (bundled in xwork-1.1.jar);
Declare the class in your XML configuration file ( xworkaction.xml) using the element <interceptor /> nested within <interceptors />;
Create stacks of interceptorsInterceptors, using the <interceptor-stack /> element (optional);
Determine which interceptors Interceptors are used by which actionmapping, using <interceptor-ref /> or <default-interceptor-ref />. The former defines the interceptors to be used in a specific action, while the latter determines the default interceptor stack to be used by all actions that do not specify their own <interceptor-ref />.

...

Code Block

	java
	java

package lesson05;

import java.util.Calendar;
import com.opensymphony.xwork.interceptor.Interceptor;
import com.opensymphony.xwork.ActionInvocation;

public class GreetingInterceptor implements Interceptor {
	public void init() { }
	public void destroy() { }
	public String intercept(ActionInvocation invocation) throws Exception {
		Calendar calendar = Calendar.getInstance();
		int hour = calendar.get(Calendar.HOUR_OF_DAY);
		String greeting = (hour < 6) ? "Good evening" :
			((hour < 12) ? "Good morning":
			((hour < 18) ? "Good afternoon": "Good evening"));

		invocation.getInvocationContext().getSession().put("greeting", greeting);

		String result = invocation.invoke();

		return result;
	}
}

xwork.xml:

Code Block

	xml
	xml

<!DOCTYPE xwork PUBLIC "-//OpenSymphony Group//XWork 1.0//EN"
"http://www.opensymphony.com/xwork/xwork-1.0.dtd">

<xwork>
	<!-- Include webwork defaults (from WebWork JAR). -->
	<include file="webwork-default.xml" />

	<!-- Configuration for the default package. -->
	<package name="default" extends="webwork-default">
		<interceptors>
			<interceptor name="greeting" class="section02.lesson05.GreetingInterceptor" />
		</interceptors>

		<!-- Action: Lesson 5: GreetingInterceptor. -->
		<action name="greetingAction" class="lesson05.GreetingAction">
			<result name="success" type="velocity">ex01-result.vm</result>
			<interceptor-ref name="greeting" />
		</action>
	</package>
</xwork>

GreetingAction.java:

Code Block

	java
	java

package lesson05;

import com.opensymphony.xwork.ActionSupport;

public class GreetingAction extends ActionSupport {
	public String execute() throws Exception {
		return SUCCESS;
	}
}

ex01-result.vm:

Code Block

	html
	html

<html>
<head>
<title>WebWork Tutorial - Lesson 5 - Example 1</title>
</head>
<body>

#set ($ses = $req.getSession())
<p><b>${ses.getAttribute('greeting')}!</b></p>

</body>
</html>

...

Let's take a look at our interceptor class first. As explained before, the interceptor must implement com.opensymphony.xwork.interceptor.Interceptor's methods: init(), called during interceptor initialization, destroy(), called during destruction, and most importantly, intercept(ActionInvocation invocation), which is where we place the code that does the work.

...

Child pages

Versions Compared

Old Version 14

New Version 15

Key

Interceptors

Interceptor configuration:

Configuring Interceptors

Stacking Interceptors

`action-default.xml`

Building your own Interceptor

xwork.xml:

GreetingAction.java:

ex01-result.vm:

Child pages

Page History

Versions Compared

Old Version 14

New Version 15

Key

Interceptors

Interceptor configuration:

Configuring Interceptors

Stacking Interceptors

action-default.xml

Building your own Interceptor

xwork.xml:

GreetingAction.java:

ex01-result.vm:

`action-default.xml`