spring MVC - Inteceptors（拦截器）

Spring的Interceptor(拦截器)是Controller 方法级别的 当某一个Controller的方法进行request处理的时候 可以通过Interceptor进行拦截, 拦截器可以在方法执行之前, 方法执行完以后(返回ModelAndView) 以及执行完整个流程(直到渲染完View) 进行拦截 

Spring MVC allow you to intercept web request through handler interceptors. The handler interceptor have to implement the org.springframework.web.servlet.HandlerInterceptor interface, which contains three methods :

1. preHandle() – Called before the handler execution, returns a boolean value, “true” : continue the handler execution chain; “false”, stop the execution chain and return it. 
2. postHandle() – Called after the handler execution, allow manipulate the ModelAndView object before render it to view page.
3. afterCompletion() – Called after the complete request has finished. Seldom use, cant find any use case.

In this tutorial, you will create two handler interceptors to show the use of the HandlerInterceptor.

1. ExecuteTimeInterceptor – Intercept the web request, and log the controller execution time.
2. MaintenanceInterceptor – Intercept the web request, check if the current time is in between the maintenance time, if yes then redirect it to maintenance page.

Note
It’s recommended to extend the HandlerInterceptorAdapter for the convenient default implementations.

1. ExecuteTimeInterceptor

Intercept the before and after controller execution, log the start and end of the execution time, save it into the existing intercepted controller’s modelAndView for later display.

File : ExecuteTimeInterceptor.java

package com.mkyong.common.interceptor;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.log4j.Logger;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class ExecuteTimeInterceptor extends HandlerInterceptorAdapter{

    private static final Logger logger = Logger.getLogger(ExecuteTimeInterceptor.class);

    //before the actual handler will be executed
    public boolean preHandle(HttpServletRequest request,
        HttpServletResponse response, Object handler)
        throws Exception {

        long startTime = System.currentTimeMillis();
        request.setAttribute("startTime", startTime);

        return true;
    }

    //after the handler is executed
    public void postHandle(
        HttpServletRequest request, HttpServletResponse response,
        Object handler, ModelAndView modelAndView)
        throws Exception {

        long startTime = (Long)request.getAttribute("startTime");

        long endTime = System.currentTimeMillis();

        long executeTime = endTime - startTime;

        //modified the exisitng modelAndView
        modelAndView.addObject("executeTime",executeTime);

        //log it
        if(logger.isDebugEnabled()){
           logger.debug("[" + handler + "] executeTime : " + executeTime + "ms");
        }
    }
}

2. MaintenanceInterceptor

Intercept before the controller execution, check if the current time is in between the maintenance time, if yes then redirect it to maintenance page; else continue the execution chain.

File : MaintenanceInterceptor.java

package com.mkyong.common.interceptor;

import java.util.Calendar;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class MaintenanceInterceptor extends HandlerInterceptorAdapter{

    private int maintenanceStartTime;
    private int maintenanceEndTime;
    private String maintenanceMapping;

    public void setMaintenanceMapping(String maintenanceMapping) {
        this.maintenanceMapping = maintenanceMapping;
    }

    public void setMaintenanceStartTime(int maintenanceStartTime) {
        this.maintenanceStartTime = maintenanceStartTime;
    }

    public void setMaintenanceEndTime(int maintenanceEndTime) {
        this.maintenanceEndTime = maintenanceEndTime;
    }

    //before the actual handler will be executed
    public boolean preHandle(HttpServletRequest request,
            HttpServletResponse response, Object handler)
        throws Exception {

        Calendar cal = Calendar.getInstance();
        int hour = cal.get(cal.HOUR_OF_DAY);

        if (hour >= maintenanceStartTime && hour <= maintenanceEndTime) {
            //maintenance time, send to maintenance page
            response.sendRedirect(maintenanceMapping);
            return false;
        } else {
            return true;
        }

    }
}

3. Enable the handler interceptor

To enable it, put your handler interceptor class in the handler mapping “interceptors” property.

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="mappings">
            <props>
                <prop key="/welcome.htm">welcomeController</prop>
            </props>
        </property>
        <property name="interceptors">
            <list>
                <ref bean="maintenanceInterceptor" />
                <ref bean="executeTimeInterceptor" />
            </list>
        </property>
    </bean>

    <bean
    class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping">
        <property name="interceptors">
            <list>
                <ref bean="executeTimeInterceptor" />
            </list>
        </property>
    </bean>

    <bean id="welcomeController"
                  class="com.mkyong.common.controller.WelcomeController" />
    <bean class="com.mkyong.common.controller.MaintenanceController" />

    <bean id="executeTimeInterceptor"
                 class="com.mkyong.common.interceptor.ExecuteTimeInterceptor" />

    <bean id="maintenanceInterceptor"
                class="com.mkyong.common.interceptor.MaintenanceInterceptor">
        <property name="maintenanceStartTime" value="23" />
        <property name="maintenanceEndTime" value="24" />
        <property name="maintenanceMapping" value="/SpringMVC/maintenance.htm" />
    </bean>

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix">
            <value>/WEB-INF/pages/</value>
        </property>
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>

</beans>

4. Enable the handler interceptor other

<!-- 1.拦截器按照先后顺序进行拦截，2.拦截全部请求时使用"/**"， 3.拦截只针对controller -->
<mvc:interceptors>
    <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor" />

    <mvc:interceptor>
        <mapping path="/secure/*" />
        <bean class="com.example.interceptor.SecurityInterceptor" />
    </mvc:interceptor>
    <mvc:interceptor>
        <mapping path="/admin/*.do" />
        <bean class="com.example.interceptor.admin.ControlInterceptor" />
    </mvc:interceptor>
</mvc:interceptors>

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