Servlet之监听器

Servlet

监听器

1. 监听器的类型
   ServletContextListener 监听web应用（ServletContext）对象的创建和销毁
   ServletContextAttributeListener 监听web应用（ServletContext）对象的属性
   HttpSessionListener 监听session对象的创建和销毁
   HttpSessionAttributeListener 监听session对象的属性
   ServletRequestListener 监听request对象的创建和销毁
   ServletRequestAttributeListener 监听request对象的属性
   HttpSessionActivationListener 服务器暂时性的停止时，把session里存储的对象暂时存到硬盘上（钝化），把硬盘上的数据恢复为对象（活化）
   HttpSessionBindingListener 属性绑定与解除绑定，当把对象存储到session中时，调用属性绑定方法，当session失效或者把该对象从session中移除时，调用解除绑定方法
2. 前六种监听器的使用
   以前两种（ServletContext相关）举例

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <listener>
    <listener-class>com.java.listener.MyListener</listener-class>
  </listener>
</web-app>

/**
 * 监听web应用（ServletContext）对象的创建和销毁
 */
//@WebListener
public class MyListener implements ServletContextListener {

    public MyListener() {
       
    }
    public void contextDestroyed(ServletContextEvent arg0)  { 
        System.out.println("contextDestroyed");
    }
    public void contextInitialized(ServletContextEvent arg0)  { 
        System.out.println("contextInitialized");
    }
	
}

/**
 * 监听web应用（ServletContext）对象的属性
 */
@WebListener
public class MyAttrListener implements ServletContextAttributeListener {

    public MyAttrListener() {
        
    }
    //setAttribute("name","admin1");
    public void attributeAdded(ServletContextAttributeEvent arg0)  { 
       System.out.println("attributeAdded");
    }
    //removeAttribute("name");
    public void attributeRemoved(ServletContextAttributeEvent arg0)  { 
    	System.out.println("attributeRemoved");
    }
    //setAttribute("name","admin2");
    public void attributeReplaced(ServletContextAttributeEvent arg0)  { 
        System.out.println("attributeReplaced");
    }
	
}

@WebServlet("/MyServlet")
public class MyServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException ,IOException {
	   ServletContext sc = this.getServletContext();
	   System.out.println("----------------添加属性-----------------");
	   sc.setAttribute("name", "admin1");
	   System.out.println("----------------修改属性-----------------");
	   sc.setAttribute("name", "admin2");
	   System.out.println("----------------删除属性-----------------");
	   sc.removeAttribute("name");
    }
}

3. HttpSessionActivationListener使用

public class Student implements Serializable, HttpSessionActivationListener{
	private String name;

	public Student() {
		super();
		// TODO Auto-generated constructor stub
	}

	public Student(String name) {
		super();
		this.name = name;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
	/**
	 * 活化
	 */
	@Override
	public void sessionDidActivate(HttpSessionEvent se) {
		System.out.println("sessionDidActivate");
	}
	/**
	 * 钝化
	 */
	@Override
	public void sessionWillPassivate(HttpSessionEvent se) {
		System.out.println("sessionWillPassivate");
	}
	
}

@WebServlet("/SetSessionServlet")
public class SetSessionServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException ,IOException {
    	req.getSession().setAttribute("stu", new Student("admin"));
    }
}

@WebServlet("/GetSessionServlet")
public class GetSessionServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException ,IOException {
    	Student stu = (Student)req.getSession().getAttribute("stu");
    	System.out.println(stu.getName());
    }
}

4. HttpSessionBindingListener使用

public class Person implements Serializable, HttpSessionBindingListener{
	private String name;

	public Person() {
		super();
		// TODO Auto-generated constructor stub
	}

	public Person(String name) {
		super();
		this.name = name;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
	/**
	 * 属性绑定
	 * setAttribute
	 */
	@Override
	public void valueBound(HttpSessionBindingEvent event) {
		System.out.println("valueBound");
	}
	/**
	 * 解除绑定
	 * session失效
	 * removeAttribute
	 */
	@Override
	public void valueUnbound(HttpSessionBindingEvent event) {
		System.out.println("valueUnbound");
	}
	
}

@WebServlet("/BindSessionServlet")
public class BindSessionServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException ,IOException {
    	req.getSession().setAttribute("person", new Person("admin"));
    	req.getSession().invalidate();
    }
}