比如,当我要添加一个信用卡的时候,我需要信用卡的CardType, 这些数据是存在数据库中的,我要先通过action 的一个 create方法,取到信用卡的类型:
creditCardTypeList = this.creditCardTypeService.getList();
return SUCCESS;
}
Struts的配置文件:
</action>
input.jsp
<s:select name="creditCard.creditCardTypeId" list="creditCardTypeList" listKey="creditCardTypeId"
listValue="ccType" />
....
当提交input.jsp 的时候,Validate 检查没有通过,这时我需要回到input.jsp,此时应该下拉列表框的CreditType应该被保留,只需要在example.CreditCardAction 实现 Preparable接口,并实现prepare 方法,然后在add的 action中加上
<interceptor-ref name="defaultStack"/>
就可以了
prepare方法:
creditCardTypeList = this.creditCardTypeService.getList();
}
Add Acton:
<interceptor-ref name="prepare"/>
<interceptor-ref name="defaultStack"/>
<result name="input">input.jsp</result>
<result name="success" type="redirect-action">
<param name="namespace">/credit</param>
<param name="actionName">list</param>
</result>
</action>
这样,在验证前将首先调用 prepare方法,即使失败了回到input.jsp页面creditCardType选择框的值仍然存在。
<interceptor-ref name="defaultStack"/> 中的 defaultStack 是我们在struts.xml 中配置的,其中我们注释掉了 <interceptor-ref name="prepare"/> 这样在example.CreditCardAction中的其他Action就不会首先执行prepare方法,只有加上了 <interceptor-ref name="prepare"/> 的才会去首先执行 prepare方法。
<interceptors>
<interceptor-stack name="defaultStack">
<interceptor-ref name="exception"/>
<interceptor-ref name="alias"/>
<interceptor-ref name="servletConfig"/>
<!--
<interceptor-ref name="prepare"/>
-->
<interceptor-ref name="i18n"/>
<interceptor-ref name="chain"/>
<interceptor-ref name="debugging"/>
<interceptor-ref name="profiling"/>
<interceptor-ref name="scopedModelDriven"/>
<interceptor-ref name="modelDriven"/>
<interceptor-ref name="fileUpload"/>
<!--
<interceptor-ref name="checkbox">
<param name="uncheckedValue">no</param>
</interceptor-ref>
-->
<interceptor-ref name="staticParams"/>
<interceptor-ref name="params">
<param name="excludeParams">dojo..*</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>
</interceptors>
</package>
现在看下PrepareInterceptor拦截器的源代码:
public String doIntercept(ActionInvocation invocation) throws Exception {
Object action = invocation.getAction();
if (action instanceof Preparable) { //判断这个action是否是Preparable类的一个实例,也就是判断这个action有没有implement实现这个Preparable借口
try {
String[] prefixes;
if (firstCallPrepareDo) {
prefixes = new String[] {ALT_PREPARE_PREFIX, PREPARE_PREFIX};
} else {
prefixes = new String[] {PREPARE_PREFIX, ALT_PREPARE_PREFIX};
}
PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes);
}
catch (InvocationTargetException e) {
/*
* The invoked method threw an exception and reflection wrapped it
* in an InvocationTargetException.
* If possible re-throw the original exception so that normal
* exception handling will take place.
*/
Throwable cause = e.getCause();
if (cause instanceof Exception) {
throw (Exception) cause;
} else if(cause instanceof Error) {
throw (Error) cause;
} else {
/*
* The cause is not an Exception or Error (must be Throwable) so
* just re-throw the wrapped exception.
*/
throw e;
}
}
if (alwaysInvokePrepare) {
((Preparable) action).prepare();
}
}
return invocation.invoke();
}