自定义拦截器和提供的拦截器

在访问struts2中某个action之后或者之前，会自动调用的类，就是struts2中的拦截器

一，怎样自定义拦截器

自定义一个拦截器需要三步：
1 ，自定义一个实现Interceptor接口（或者继承自AbstractInterceptor）的类。
2 ，在struts.xml中注册上一步中定义的拦截器。
3 ，在需要使用的Action中引用上述定义的拦截器，为了方便也可将拦截器定义为默认的拦截器，这样在不加特殊声明的情况下所有的Action都被这个拦截器拦截。

Interceptor接口声明了三个方法：

public interface Interceptor extends Serializable {     void destroy();     void init();     String intercept(ActionInvocation invocation) throws Exception;}

Init方法在拦截器类被创建之后，使用这个方法可以给拦截器类做必要的初始话操作，主要用于初始化系统资源，如打开数据库资源

Destroy方法在拦截器被垃圾回收之前调用，用来回收init方法初始化的资源。

Intercept是拦截器的主要拦截方法，如果需要调用后续的Action或者拦截器，只需要在该方法中调用invocation.invoke()方法即可，在该方法调用的前后可以插入Action调用前后拦截器需要做的方法。
如果不需要调用后续的方法，则返回一个String类型的对象即可，例Action.SUCCESS，即可返回Action中SUCCESS逻辑视图的字符串对应的jsp

另外AbstractInterceptor提供了一个简单的Interceptor的实现，这个实现为：

public abstract class AbstractInterceptor implements Interceptor {      public void init() {    }       public void destroy() {    }      public abstract String intercept(ActionInvocation invocation) throws Exception;}

所以编写拦截器时只需要继承AbstractInterceptor抽象类即可，重写使用的方法。

二，struts2提供的拦截器功能说明

struts2提供的拦截器的作用：

sturts2本身只是一个空的容器，而是大量的拦截器让struts2拥有非常强大的功能，比如防止表单重复提交，进行输入校验…打开struts2-core.jar包下的struts-default.xml中看到struts2都实现了哪些拦截器。struts-default.xml这个文件是写struts.xml时需要继承的xml文件，其中就声明了大量的拦截器和拦截器栈。我们可以找到defaultStack这个拦截器栈，它就是struts2默认加载的拦截器栈，他提供了struts2的基本操作，比如得到参数并将参数赋值给对应的action中的属性……

注：当我们手动为某个action添加一个拦截器的时候，会让defaultStack自动无效，所以需要首先引用defaultStack然后再添加其他的拦截器

struts-default.xml

<package name="struts-default" abstract="true">        <result-types>            <result-type name="chain" class="com.opensymphony.xwork2.ActionChainResult"/>            <result-type name="dispatcher" class="org.apache.struts2.dispatcher.ServletDispatcherResult" default="true"/>            <result-type name="freemarker" class="org.apache.struts2.views.freemarker.FreemarkerResult"/>            <result-type name="httpheader" class="org.apache.struts2.dispatcher.HttpHeaderResult"/>            <result-type name="redirect" class="org.apache.struts2.dispatcher.ServletRedirectResult"/>            <result-type name="redirectAction" class="org.apache.struts2.dispatcher.ServletActionRedirectResult"/>            <result-type name="stream" class="org.apache.struts2.dispatcher.StreamResult"/>            <result-type name="velocity" class="org.apache.struts2.dispatcher.VelocityResult"/>            <result-type name="xslt" class="org.apache.struts2.views.xslt.XSLTResult"/>            <result-type name="plainText" class="org.apache.struts2.dispatcher.PlainTextResult" />        </result-types>        <interceptors>            <interceptor name="alias" class="com.opensymphony.xwork2.interceptor.AliasInterceptor"/>            <interceptor name="autowiring" class="com.opensymphony.xwork2.spring.interceptor.ActionAutowiringInterceptor"/>            <interceptor name="chain" class="com.opensymphony.xwork2.interceptor.ChainingInterceptor"/>            <interceptor name="conversionError" class="org.apache.struts2.interceptor.StrutsConversionErrorInterceptor"/>            <interceptor name="cookie" class="org.apache.struts2.interceptor.CookieInterceptor"/>            <interceptor name="clearSession" class="org.apache.struts2.interceptor.ClearSessionInterceptor" />            <interceptor name="createSession" class="org.apache.struts2.interceptor.CreateSessionInterceptor" />            <interceptor name="debugging" class="org.apache.struts2.interceptor.debugging.DebuggingInterceptor" />            <interceptor name="externalRef" class="com.opensymphony.xwork2.interceptor.ExternalReferencesInterceptor"/>            <interceptor name="execAndWait" class="org.apache.struts2.interceptor.ExecuteAndWaitInterceptor"/>            <interceptor name="exception" class="com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor"/>            <interceptor name="fileUpload" class="org.apache.struts2.interceptor.FileUploadInterceptor"/>            <interceptor name="i18n" class="com.opensymphony.xwork2.interceptor.I18nInterceptor"/>            <interceptor name="logger" class="com.opensymphony.xwork2.interceptor.LoggingInterceptor"/>            <interceptor name="modelDriven" class="com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor"/>            <interceptor name="scopedModelDriven" class="com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor"/>            <interceptor name="params" class="com.opensymphony.xwork2.interceptor.ParametersInterceptor"/>            <interceptor name="actionMappingParams" class="org.apache.struts2.interceptor.ActionMappingParametersInteceptor"/>            <interceptor name="prepare" class="com.opensymphony.xwork2.interceptor.PrepareInterceptor"/>            <interceptor name="staticParams" class="com.opensymphony.xwork2.interceptor.StaticParametersInterceptor"/>            <interceptor name="scope" class="org.apache.struts2.interceptor.ScopeInterceptor"/>            <interceptor name="servletConfig" class="org.apache.struts2.interceptor.ServletConfigInterceptor"/>            <interceptor name="sessionAutowiring" class="org.apache.struts2.spring.interceptor.SessionContextAutowiringInterceptor"/>            <interceptor name="timer" class="com.opensymphony.xwork2.interceptor.TimerInterceptor"/>            <interceptor name="token" class="org.apache.struts2.interceptor.TokenInterceptor"/>            <interceptor name="tokenSession" class="org.apache.struts2.interceptor.TokenSessionStoreInterceptor"/>            <interceptor name="validation" class="org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor"/>            <interceptor name="workflow" class="com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor"/>            <interceptor name="store" class="org.apache.struts2.interceptor.MessageStoreInterceptor" />            <interceptor name="checkbox" class="org.apache.struts2.interceptor.CheckboxInterceptor" />            <interceptor name="profiling" class="org.apache.struts2.interceptor.ProfilingActivationInterceptor" />            <interceptor name="roles" class="org.apache.struts2.interceptor.RolesInterceptor" />            <interceptor name="jsonValidation" class="org.apache.struts2.interceptor.validation.JSONValidationInterceptor" />            <interceptor name="annotationWorkflow" class="com.opensymphony.xwork2.interceptor.annotations.AnnotationWorkflowInterceptor" />            <interceptor name="multiselect" class="org.apache.struts2.interceptor.MultiselectInterceptor" />            <!-- Basic stack -->            <interceptor-stack name="basicStack">                <interceptor-ref name="exception"/>                <interceptor-ref name="servletConfig"/>                <interceptor-ref name="prepare"/>                <interceptor-ref name="checkbox"/>                <interceptor-ref name="multiselect"/>                <interceptor-ref name="actionMappingParams"/>                <interceptor-ref name="params">                    <param name="excludeParams">dojo\..*,^struts\..*</param>                </interceptor-ref>                <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 JSON validation stack -->            <interceptor-stack name="jsonValidationWorkflowStack">                <interceptor-ref name="basicStack"/>                <interceptor-ref name="validation">                    <param name="excludeMethods">input,back,cancel</param>                </interceptor-ref>                <interceptor-ref name="jsonValidation"/>                <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 model-driven stack  -->            <interceptor-stack name="modelDrivenStack">                <interceptor-ref name="modelDriven"/>                <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="i18nStack">                <interceptor-ref name="i18n"/>                <interceptor-ref name="basicStack"/>            </interceptor-stack>            <!-- An example of the paramsPrepareParams trick. This stack                 is exactly the same as the defaultStack, except that it                 includes one extra interceptor before the prepare interceptor:                 the params interceptor.                 This is useful for when you wish to apply parameters directly                 to an object that you wish to load externally (such as a DAO                 or database or service layer), but can't load that object                 until at least the ID parameter has been loaded. By loading                 the parameters twice, you can retrieve the object in the                 prepare() method, allowing the second params interceptor to                 apply the values on the object. -->            <interceptor-stack name="paramsPrepareParamsStack">                <interceptor-ref name="exception"/>                <interceptor-ref name="alias"/>                <interceptor-ref name="i18n"/>                <interceptor-ref name="checkbox"/>                <interceptor-ref name="multiselect"/>                <interceptor-ref name="params">                    <param name="excludeParams">dojo\..*,^struts\..*</param>                </interceptor-ref>                <interceptor-ref name="servletConfig"/>                <interceptor-ref name="prepare"/>                <interceptor-ref name="chain"/>                <interceptor-ref name="modelDriven"/>                <interceptor-ref name="fileUpload"/>                <interceptor-ref name="staticParams"/>                <interceptor-ref name="actionMappingParams"/>                <interceptor-ref name="params">                    <param name="excludeParams">dojo\..*,^struts\..*</param>                </interceptor-ref>                <interceptor-ref name="conversionError"/>                <interceptor-ref name="validation">                    <param name="excludeMethods">input,back,cancel,browse</param>                </interceptor-ref>                <interceptor-ref name="workflow">                    <param name="excludeMethods">input,back,cancel,browse</param>                </interceptor-ref>            </interceptor-stack>            <!-- A complete stack with all the common interceptors in place.                 Generally, this stack should be the one you use, though it                 may do more than you need. Also, the ordering can be                 switched around (ex: if you wish to have your servlet-related                 objects applied before prepare() is called, you'd need to move                 servletConfig interceptor up.                 This stack also excludes from the normal validation and workflow                 the method names input, back, and cancel. These typically are                 associated with requests that should not be validated.                 -->            <interceptor-stack name="defaultStack">                <interceptor-ref name="exception"/>                <interceptor-ref name="alias"/>                <interceptor-ref name="servletConfig"/>                <interceptor-ref name="i18n"/>                <interceptor-ref name="prepare"/>                <interceptor-ref name="chain"/>                <interceptor-ref name="debugging"/>                <interceptor-ref name="scopedModelDriven"/>                <interceptor-ref name="modelDriven"/>                <interceptor-ref name="fileUpload"/>                <interceptor-ref name="checkbox"/>                <interceptor-ref name="multiselect"/>                <interceptor-ref name="staticParams"/>                <interceptor-ref name="actionMappingParams"/>                <interceptor-ref name="params">                  <param name="excludeParams">dojo\..*,^struts\..*</param>                </interceptor-ref>                <interceptor-ref name="conversionError"/>                <interceptor-ref name="validation">                    <param name="excludeMethods">input,back,cancel,browse</param>                </interceptor-ref>                <interceptor-ref name="workflow">                    <param name="excludeMethods">input,back,cancel,browse</param>                </interceptor-ref>            </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>            <!-- Sample execute and wait stack.                 Note: execAndWait should always be the *last* interceptor. -->            <interceptor-stack name="executeAndWaitStack">                <interceptor-ref name="execAndWait">                    <param name="excludeMethods">input,back,cancel</param>                </interceptor-ref>                <interceptor-ref name="defaultStack"/>                <interceptor-ref name="execAndWait">                    <param name="excludeMethods">input,back,cancel</param>                </interceptor-ref>            </interceptor-stack>       </interceptors>        <default-interceptor-ref name="defaultStack"/>        <default-class-ref class="com.opensymphony.xwork2.ActionSupport" />    </package>