SpringMVC:拦截器

1.配置拦截器

SpringMVC中的拦截器用于拦截控制器方法的执行
SpringMVC中的拦截器需要实现HandlerInterceptor
SpringMVC的拦截器必须在SpringMVC的配置文件中进行配置：

3中方法

<!-- 第一第二种 配置方式都是对DispatcherServlet所处理的所有的请求进行拦截-->

1. <!--配置拦截器-->
     <mvc:interceptors>
       <bean class="com.tinstu.mvn.interceptors.FristInterceptor"></bean>-->
     </mvc:interceptors>

2. <!--配置拦截器-->
      <mvc:interceptors>
       <ref bean="firstInterceptors"></ref>
      </mvc:interceptors>

3. <!--配置拦截器-->
       <mvc:interceptors>
            <mvc:interceptor>
               <mvc:mapping path="/**"/>
               <mvc:exclude-mapping path="/testRequestEntity"/>
               <ref bean="firstInterceptor"></ref>
            </mvc:interceptor>
       </mvc:interceptors>
       <!--
       此配置方式可以通过ref或bean标签设置拦截器，
       通过mvc:mapping设置需要拦截的请求，
       通过mvc:exclude-mapping设置需要排除的请求，即不需要拦截的请求
       -->

 2.拦截器的三个方法

SpringMVC中的拦截器有三个抽象的方法

1. perHandle：控制器方法执行之前执行preHandle( ) ,其boolean类型返回值表示是否拦截或放行，返回为true为放行，即调用控制器方法；返回false表示拦截，即不调用控制器方法.
2. postHandle：控制器方法执行之后执行postHandle( )
3. afterComplation：处理完视图和模型数据。渲染视图完毕之后执行afterComlation( )

创建两个拦截器：FirstInterceptors.java  secondInterceors.java

package com.tinstu.mvn.interceptors;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@Component
public class FirstInterceptors implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle!!!!");
        return true;

    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
        System.out.println("postHandle!!!!");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
        System.out.println("afterCompletion!!!");
    }
}

package com.tinstu.mvn.interceptors;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@Component
public class SecondInterceptors implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("SecondInterceptors preHandle!!!!");
        return true;

    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
        System.out.println("SecondInterceptors postHandle!!!!");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
        System.out.println("SecondInterceptors afterCompletion!!!");
    }
}

3.多个拦截器的执行顺序

（1）若每个拦截器的preHandle的返回值都为true

此时多个拦截器的执行顺序和拦截器在SpringMVC的配置文件的配置顺序有关：
preHandle()会按照配置的顺序执行，而postHandle()和afterComplation()会按照配置的反序执行

使用上面的两个拦截器：

springmvc.xml 配置如下

    <mvc:interceptors>
    <!--1-->
        <bean class="com.tinstu.mvn.interceptors.FristInterceptor"></bean>
        <bean class="com.tinstu.mvn.interceptors.SecondInterceptors"></bean>
    <mvc:interceptors>

控制台输出结果：

（2）若某个拦截器的preHandle返回了 false

preHandle()返回false和它之前的拦截器的preHandle()都会执行，postHandle()都不执行，返回false
的拦截器之前的拦截器的afterComplation()会执行

再添加一个拦截器No3Interceptors，将secondinterceptors的proHandle返回值改为false