Spring提供了一个 “ContextLoaderListener” 监听器，以使 Spring 依赖注入到会话监听器。 在本教程中，通过添加一个 Spring 依赖注入一个bean 到会话监听器修改 HttpSessionListener 例子。
1. Spring Beans
创建一个简单的计数服务来打印创建的会话总数。
File : CounterService.java
package com.yiibai.common;
public class CounterService{
public void printCounter(int count){
System.out.println("Total session created : " + count);
}
}
File : counter.xml – Bean配置文件
<?xml version="1.0" encoding="UTF-8"?> <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 id="counterService" class="com.yiibai.common.CounterService" /> </beans>
2. WebApplicationContextUtils
使用“WebApplicationContextUtils”来获得 Spring 上下文，以后可以得到任何声明Spring的Bean 在一个正常的 Spring 方式。
File : SessionCounterListener.java
package com.yiibai.common;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import org.springframework.context.ApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
public class SessionCounterListener implements HttpSessionListener {
private static int totalActiveSessions;
public static int getTotalActiveSession(){
return totalActiveSessions;
}
@Override
public void sessionCreated(HttpSessionEvent arg0) {
totalActiveSessions++;
System.out.println("sessionCreated - add one session into counter");
printCounter(arg0);
}
@Override
public void sessionDestroyed(HttpSessionEvent arg0) {
totalActiveSessions--;
System.out.println("sessionDestroyed - deduct one session from counter");
printCounter(arg0);
}
private void printCounter(HttpSessionEvent sessionEvent){
HttpSession session = sessionEvent.getSession();
ApplicationContext ctx =
WebApplicationContextUtils.
getWebApplicationContext(session.getServletContext());
CounterService counterService =
(CounterService) ctx.getBean("counterService");
counterService.printCounter(totalActiveSessions);
}
}
3. 集成
唯一的问题是，如何使 Web 应用程序知道在哪里可以加载 Spring bean 配置文件？秘诀是在“web.xml”文件中。
-
注册“ContextLoaderListener”作为第一个监听器，使Web应用程序知道Spring上下文加载程序。
-
配置“contextConfigLocation”，并定义Spring的bean配置文件。
File : web.xml
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
<display-name>Archetype Created Web Application</display-name>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/Spring/counter.xml</param-value>
</context-param>
<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
<listener>
<listener-class>
com.yiibai.common.SessionCounterListener
</listener-class>
</listener>
<servlet>
<servlet-name>Spring DI Servlet Listener</servlet-name>
<servlet-class>com.yiibai.common.App</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Spring DI Servlet Listener</servlet-name>
<url-pattern>/Demo</url-pattern>
</servlet-mapping>
</web-app>
File : App.java
package com.yiibai.common;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class App extends HttpServlet{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException{
HttpSession session = request.getSession(); //sessionCreated() is executed
session.setAttribute("url", "yiibai.com");
session.invalidate(); //sessionDestroyed() is executed
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<body>");
out.println("<h1>Spring Dependency Injection into Servlet Listenner</h1>");
out.println("</body>");
out.println("</html>");
}
}
启动Tomcat，并访问 URL “http://localhost:8080/7.2-SpringDemo/"
输出结果
sessionCreated - add one session into counter Total session created : 1 sessionDestroyed - deduct one session from counter Total session created : 0
看看控制台的输出，会得到通过 Spring DI 记数服务的 bean，并打印会话的总数。
总结
在Spring中，“ContextLoaderListener”是一个通用的方法集成Spring依赖注入到几乎所有的Web应用程序。
