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Spring MVC Handler Interceptor example

source: http://www.mkyong.com/spring-mvc/spring-mvc-handler-interceptors-example/
Spring MVC allow you to intercept web request through handler interceptors. The handler interceptor have to implement the 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 one handler interceptor to show the use of the HandlerInterceptor.
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.
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
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;
  }
 
 }
}

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

 
 <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>

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