struts2 Preparable接口

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>