Handler Interceptor

如果您在Controller執行的前後，或者是在View繪製之後打算作一些記錄或欄截請求等動作，您可以實作 org.springframework.web.servlet.HandlerInterceptor介面，在這個介面中規範了三個必須實作的方法，其定義如下所示：

package org.springframework.web.servlet;

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

public interface HandlerInterceptor {
    boolean preHandle(HttpServletRequest request,
                HttpServletResponse response,
                    Object handler) throws Exception;
    void postHandle(HttpServletRequest request,
               HttpServletResponse response,
                  Object handler,
                  ModelAndView modelAndView)    throws Exception;
    void afterCompletion(HttpServletRequest request,
               HttpServletResponse response,
Object handler,
Exception ex) throws Exception;
}

preHandler()會在Controller處理請求之前被呼叫，傳回的boolean快定是否呼叫接下來的Handler Interceptor或是Controller來處理請求，如果傳回false，則接下來的Interceptor或Controller就不處理請求，postHandler()則會在Controller處理完請求之後被呼叫，afterCompletion()方法會在View繪製完成之後被呼叫。

您可以直接繼承org.springframework.web.servlet.handler.HandlerInterceptorAdapter，它實作了HandlerInterceptor介面，您只要針對您有興趣的方法進行重新定義就可以了，例如可以修改第一個 Spring MVC 程式，在當中實作一個LoggingInterceptor，在請求被控制物件處理的前、後來作記錄：

LoggingInterceptor.java

package onlyfun.caterpillar;

import java.util.logging.Logger;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.
                  handler.HandlerInterceptorAdapter;

public class LoggingInterceptor 
        extends HandlerInterceptorAdapter {
    private Logger logger = 
            Logger.getLogger(this.getClass().getName());
    
    public boolean preHandle(HttpServletRequest request,
                    HttpServletResponse response, 
                    Object handler) throws Exception {
        logger.info(
                handler.getClass().getName() + " 開始執行...");
        return true;
    }
    
    public void postHandle(HttpServletRequest request, 
                HttpServletResponse response, 
                Object handler, 
                ModelAndView modelAndView) throws Exception {
        logger.info(
                handler.getClass().getName() + " 執行完畢...");
    }
    
    public void afterCompletion(HttpServletRequest request,
                HttpServletResponse response, 
                Object handler, 
                Exception ex) throws Exception {
        logger.info("請求處理完畢...");
    }
}

要使用定義好的HandlerInterceptor，必須在Bean定義檔中進行定義，例如：

mvc-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC 
 "-//SPRING/DTD BEAN/EN" 
 "http://www.springframework.org/dtd/spring-beans.dtd"> 

<beans>   
    <bean id="loggingInterceptor" 
          class="onlyfun.caterpillar.LoggingInterceptor"/>

    <bean id="viewResolver"
          class="org.springframework.web.servlet.
                   → view.InternalResourceViewResolver"> 
        <property name="prefix">
            <value>/WEB-INF/jsp/</value>
        </property>
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>
              
    <bean id="urlHandlerMapping"
          class="org.springframework.web.servlet.
                   → handler.SimpleUrlHandlerMapping">
        <property name="interceptors">
            <list>
                <ref bean="loggingInterceptor"/>
            </list>
        </property>
        <property name="mappings">
            <props>
                <prop key="/hello.do">helloController</prop>
            </props>
        </property>
    </bean>
    
    <bean id="helloController" 
          class="onlyfun.caterpillar.HelloController"> 
        <property name="viewPage"> 
            <value>hello</value> 
        </property> 
    </bean>
</beans>

注意到這邊所使用的UrlHandlerMapping是SimpleUrlHandlerMapping；當您透過DispatcherServlet請求時，則在請求被處理的前後都會被記錄下動作及所處理請求的控制物件，在控制台所看到的資訊如下所示：

2005/12/30 上午 12:03:24 onlyfun.caterpillar.LoggingInterceptor preHandle
資訊: onlyfun.caterpillar.HelloController 開始執行...
2005/12/30 上午 12:03:24 onlyfun.caterpillar.LoggingInterceptor postHandle
資訊: onlyfun.caterpillar.HelloController 執行完畢...
2005/12/30 上午 12:03:24 onlyfun.caterpillar.LoggingInterceptor afterCompletion
資訊: 請求處理完畢...