SpingMVC之拦截器

Spring Web MVC的处理器拦截器  双向  request  response

类似于Servlet开发中的过滤器Filter，用于对处理器进行预处理和后处理。

拦截器拦截的请求是建立在前端控制器配置之下的，若DispatcherServlet拦截的是*.action，则拦截器即使配置 /**，则拦截器拦截的也只是所有 *.action的请求。若DispatcherServlet拦截的是 /，则拦截器配置 /**才是拦截所有资源。

preHandle：预处理回调方法，实现处理器的预处理（如登录检查），第三个参数为响应的处理器（如我们上一章的Controller实现）；

           返回值：true表示继续流程（如调用下一个拦截器或处理器）；

                     false表示流程中断（如登录检查失败），不会继续调用其他的拦截器或处理器，此时我们需要通过response来产生响应；

postHandle：后处理回调方法，实现处理器的后处理（但在渲染视图之前），此时我们可以通过modelAndView（模型和视图对象）对模型数据进行处理或对视图进行处理，modelAndView也可能为null。

afterCompletion：整个请求处理完毕回调方法，即在视图渲染完毕时回调，如性能监控中我们可以在此记录结束时间并输出消耗时间，还可以进行一些资源清理，类似于try-catch-finally中的finally，但仅调用处理器执行链中preHandle返回true的拦截器的afterCompletion。

下边是springMVC的拦截器实现

一.定义拦截器 (单个拦截器) 实现HandlerInterceptor 

拦截器
 */
public class Intecptor implements HandlerInterceptor {

    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println("preHandle====");
//这里如果返回的是false  则不执行拦截器其他的方法  如果是true 则进入另外两个方法
        return true;
    }

    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle====");
    }

    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println("afterCompletion====");
    }
}

二.xml配置  记得加注解驱动

<!--包扫描器-->
    <context:component-scan base-package="day17"></context:component-scan>

    <!--视图解析器-->
  <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/"></property>
        <property name="suffix" value=".jsp"></property>
    </bean>

    <!--单个拦截器-->
    <mvc:interceptors>
      <mvc:interceptor>
          <mvc:mapping path="/**"/>
          <bean class=" day17.Intecptor"/>
      </mvc:interceptor>
    </mvc:interceptors>

定义多个拦截器

拦截器1

/*
拦截器
 */
public class Intecptor implements HandlerInterceptor {

    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println("preHandle====");
        return true;
    }

    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println("postHandle====");
    }

    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println("afterCompletion====");
    }
}

拦截器2

public class Intecptors implements HandlerInterceptor {
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
        System.out.println("Second preHandle====");
        return true;
    }
    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        System.out.println("Second postHandle====");
    }

    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        System.out.println("Second afterCompletion====");
    }
}

xml配置

<!--包扫描器-->
    <context:component-scan base-package="day17"></context:component-scan>

    <!--视图解析器-->
  <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/"></property>
        <property name="suffix" value=".jsp"></property>
    </bean>
   
    <!--多个拦截器-->
  <!--  <mvc:interceptors>
        <mvc:interceptor>
        <mvc:mapping path="/**"/>
        <bean class=" day17.Intecptor"/>
    </mvc:interceptor>
        <mvc:interceptor>
            <mvc:mapping path="/**"/>
            <bean class=" day17.Intecptors"/>
        </mvc:interceptor>
    </mvc:interceptors>-->
    <!--注解驱动-->
<mvc:annotation-driven></mvc:annotation-driven>
        </beans>