THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
[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, 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, 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
action.xml
<package name="default" extends="action-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="redirect-action">/secure/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 interceptor-refs for each action, you can bundle these interceptors together using an interceptor stack.
action.xml
<package name="default" extends="action-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="redirect-action">/secure/home</result>
</action>
</package>
Looking inside action-default.xml we can see how it's done,
action-default.xml
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="action-default">
<result-types>
<result-type name="chain" class="com.opensymphony.xwork.ActionChainResult"/>
<result-type name="dispatcher" class="org.apache.struts.action2.dispatcher.ServletDispatcherResult"
default="true"/>
<result-type name="freemarker" class="org.apache.struts.action2.views.freemarker.FreemarkerResult"/>
<result-type name="httpheader" class="org.apache.struts.action2.dispatcher.HttpHeaderResult"/>
<result-type name="jasper" class="org.apache.struts.action2.views.jasperreports.JasperReportsResult"/>
<result-type name="redirect" class="org.apache.struts.action2.dispatcher.ServletRedirectResult"/>
<result-type name="redirect-action"
class="org.apache.struts.action2.dispatcher.ServletActionRedirectResult"/>
<result-type name="stream" class="org.apache.struts.action2.dispatcher.StreamResult"/>
<result-type name="velocity" class="org.apache.struts.action2.dispatcher.VelocityResult"/>
<result-type name="xslt" class="org.apache.struts.action2.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="org.apache.struts.action2.interceptor.WebWorkConversionErrorInterceptor"/>
<interceptor name="external-ref" class="com.opensymphony.xwork.interceptor.ExternalReferencesInterceptor"/>
<interceptor name="execAndWait" class="corg.apache.struts.action2.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="org.apache.struts.action2.interceptor.ServletConfigInterceptor"/>
<interceptor name="sessionAutowiring"
class="org.apache.struts.action2.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 action-default.xml in our action.xml, all the predefined interceptors and stacks are available for us to use in our actions.
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 |
|
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 |
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 { |
workflow |
calls the validate method in your action class. If action errors created then it returns the |
servlet-config |
give access to |
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 Interceptors, action-default.xml includes prepackaged
combinations in named Interceptor Stacks.
Building your own Interceptor
If none of the stock Interceptors meets your needs, you can implement your own Interceptor. Fortunately, this is an easy task to accomplish. Suppose we need an Interceptor that places a greeting in the session according to the time of the day (morning, afternoon or evening). Here's how we could implement it:
- Create an Interceptor class, which is a class that implements the
com.opensymphony.xwork.interceptor.Interceptorinterface (bundled inxwork-1.1.jar) - Declare the class in your XML configuration file
action.xml) using the element<interceptor />nested within<interceptors />; - Create stacks of Interceptors, using the
<interceptor-stack />element (optional); - Determine which Interceptors are used by which mapping, 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 />.
GreetingInterceptor.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:
<!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:
package lesson05;
import com.opensymphony.xwork.ActionSupport;
public class GreetingAction extends ActionSupport {
public String execute() throws Exception {
return SUCCESS;
}
}
ex01-result.vm:
<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.
Notice that our interceptor returns the result from invocation.invoke() which is the method responsible for executing the next interceptor in the stack or, if this is the last one, the action. This means that the interceptor has the power of short-circuiting the action invocation and return a result string without executing the action at all! Use this with caution, though.
One other thing that interceptors can do is execute code after the action has executed. To do that, just place code after the invocation.invoke() call. WebWork provides an abstract class that already implements this kind of behaviour: com.opensymphony.xwork.interceptor.AroundInterceptor. Just extend it and implement the methods before(ActionInvocation invocation) and after(ActionInvocation dispatcher, String result).
The xwork.xml configuration, the action class and the result page are pretty straightforward and require no further explanation.