基于注解风格的Spring-MVC的拦截器
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Spring-MVC如何使用拦截器,官方文档只给出了非注解风格的例子。那么基于注解风格如何使用拦截器呢?
基于注解基本上有2个可使用的定义类,分别是DefaultAnnotationHandlerMapping和AnnotationMethodHandlerAdapter
- < bean class ="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />
- < bean class ="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />
- <bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping"/>
- <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"/>
1、DefaultAnnotationHandlerMapping
DefaultAnnotationHandlerMapping本身支持自定义拦截器,只需按如下进行配置:
- < bean class ="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" >
- < property name = "interceptors" >
- < list >
- < bean class = "packageName.XXXInterceptor" />
- </ list >
- </ property >
- </ bean >
- <bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping">
- <property name="interceptors">
- <list>
- <bean class="packageName.XXXInterceptor" />
- </list>
- </property>
- </bean>
Interceptor的定义为:
- public class XXXInterceptor extends HandlerInterceptorAdapter {
- @Override
- public boolean preHandle(HttpServletRequest req, HttpServletResponse resp, Object handler) {
-
- String className = handler.getClass().getName();
- if (Error) {
- return false ;
- }
- return true ;
- }
- }
- public class XXXInterceptor extends HandlerInterceptorAdapter {
- @Override
- public boolean preHandle(HttpServletRequest req, HttpServletResponse resp, Object handler) {
-
- String className = handler.getClass().getName();
- if (Error) {
- return false;
- }
- return true;
- }
- }
2、AnnotationMethodHandlerAdapter
目前,笔者没找到如何给AnnotationMethodHandlerAdapter配置自定义Interceptor的方法,但是有个customArgumentResolver可以利用一下,来充当Interceptor。
- < bean class ="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" >
- < property name = "customArgumentResolver" >
- < bean class = "packageName.XXXResolver" />
- </ property >
- </ bean >
- <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
- <property name="customArgumentResolver">
- <bean class="packageName.XXXResolver"/>
- </property>
- </bean>
Resolver的定义为:
- public class XXXResolver implements WebArgumentResolver {
-
- @Override
- public Object resolveArgument(MethodParameter methodParameter, NativeWebRequest webRequest) throws Exception {
-
- String className = methodParameter.getMethod().getDeclaringClass().getName();
-
-
- HttpServletResponse resp = (HttpServletResponse) webRequest.getNativeResponse();
- HttpServletRequest req = (HttpServletRequest) webRequest.getNativeRequest();
-
- if (Error) {
- if (!resp.isCommitted()) resp.sendError(ERROR_STATUS);
- }
- return UNRESOLVED;
- }
- }
- public class XXXResolver implements WebArgumentResolver {
-
- @Override
- public Object resolveArgument(MethodParameter methodParameter, NativeWebRequest webRequest) throws Exception {
-
- String className = methodParameter.getMethod().getDeclaringClass().getName();
-
-
- HttpServletResponse resp = (HttpServletResponse) webRequest.getNativeResponse();
- HttpServletRequest req = (HttpServletRequest) webRequest.getNativeRequest();
-
- if (Error) {
- if (!resp.isCommitted()) resp.sendError(ERROR_STATUS);
- }
- return UNRESOLVED;
- }
- }
仔细的人会看出,第二种方法其实根本不是拦截。其实第二种只是在映射Controller,调用方法的时候,给每一个方法的参数增加了一个切点。
上例在出错的时候往HttpServletResponse 写错误状态,来通知web容器进行错误重定向,达到了拦截器的作用。
这么做有一个缺点,就是每个参数都有自己的切点,比如方法有3个参数就会调3次resolveArgument。为了避免出错,需要判断一下 resp.isCommitted 。
customArgumentResolver的初衷不是用来做Interceptor的,但有些环境却不得不使用它,比如部署在GAE上。
GAE 是不支持DefaultAnnotationHandlerMapping的,因为此类用到了 org.springframework.beans.BeanUtils.findEditorByConvention,这个方法会调用 java.lang.ClassLoader.getSystemClassLoader,而这正是GAE所不允许的。