spring MVC - Inteceptors（攔截器）

Spring的Interceptor(攔截器)是Controller 方法級別的 當某一個Controller的方法進行request處理的時候 可以通過Interceptor進行攔截, 攔截器可以在方法執行之前, 方法執行完以後(返回ModelAndView) 以及執行完整個流程(直到渲染完View) 進行攔截 

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.攔截器按照先後順序進行攔截，2.攔截全部請求時使用"/**"， 3.攔截只針對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>