使用场景:
如果action针对每次请求都要执行一些相同的业务逻辑, 那么可以实现Preparable接口,将预处理业务逻辑写在prepare()方法里
Preparable 接口定义:
public interface Preparable {
void prepare() throws Exception;
}
prepare何时被执行:
prepare方法由PrepareInterceptor拦截器调用执行
com.opensymphony.xwork2.interceptor.PrepareInterceptor
public String doIntercept(ActionInvocation invocation) throws Exception {
Object action = invocation.getAction();
if (action instanceof Preparable) {
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) {
// just in case there's an exception while doing reflection,
// we still want prepare() to be able to get called.
LOG.warn("an exception occured while trying to execute prefixed method", e);
}
catch (IllegalAccessException e) {
// just in case there's an exception while doing reflection,
// we still want prepare() to be able to get called.
LOG.warn("an exception occured while trying to execute prefixed method", e);
} catch (Exception e) {
// just in case there's an exception while doing reflection,
// we still want prepare() to be able to get called.
LOG.warn("an exception occured while trying to execute prefixed method", e);
}
// 必须执行或初始化的一些业务操作 action prepare()方法
if (alwaysInvokePrepare) {
((Preparable) action).prepare();
}
}
return invocation.invoke();
}
使用方法:
使用basicStack拦截器栈
<action name="list" class="org.apache.struts2.showcase.action.SkillAction" method="list">
<result>/empmanager/listSkills.jsp</result>
<interceptor-ref name="basicStack" /> <!-- 使用basicStack拦截器栈, 该拦截器栈在 struts-default.xml 已配置, 包括了prepare -->
</action>
(注: struts-default.xml 里定义的 basicStack拦截器栈
<!-- 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>
)
或者直接指定prepare拦截器
<action name="list" class="org.apache.struts2.showcase.action.SkillAction" method="list">
<result>/empmanager/listSkills.jsp</result>
<interceptor-ref name="prepare" /> <!-- 直接指定prepare拦截器 -->
</action>