Spring Boot EP 14：使用Listener監聽器管理Context、Request與Session的生命週期

Spring Boot EP 14：使用Listener監聽器管理Context、Request與Session的生命週期

Java Spring Boot開發Restful API /

2022-02-09 /

Jovepater

Listener監聽器的分類

以用途來分，大致有3種監聽器(servlet轄下，詳細如官方網站)，分別監聽對象為Context、Request、Session，並各自有不同的實現，如下表：

監聽對象初始化/銷毀屬性異動ContextServletContextListenerServletContextAttributeListenerRequestServletRequestListenerServletRequestAttributeListenerSessionHttpSessionListenerHttpSessionAttributeListener

每個監聽器其對應的方法及觸發事件如下：

監聽器方法及觸發事件ServletContextListener– contextInitialized(ServletContextEvent arg0) => 初始化– contextDestroyed(ServletContextEvent arg0) => 銷毀ServletContextAttributeListener– attributeAdded(ServletContextAttributeEvent event) => 新增屬性– attributeReplaced(ServletContextAttributeEvent event) => 修改屬性– attributeRemoved(ServletContextAttributeEvent event) => 刪除屬性ServletRequestListener– requestInitialized(ServletRequestEvent sre) => 初始化– requestDestroyed(ServletRequestEvent sre) => 銷毀ServletRequestAttributeListener– attributeAdded(ServletRequestAttributeEvent srae) => 新增屬性– attributeReplaced(ServletRequestAttributeEvent srae) => 修改屬性– attributeRemoved(ServletRequestAttributeEvent srae) => 刪除屬性HttpSessionListener– sessionCreated(HttpSessionEvent se) => 初始化– sessionDestroyed(HttpSessionEvent se) => 銷毀HttpSessionAttributeListener– attributeAdded(HttpSessionBindingEvent event) => 新增屬性– attributeReplaced(HttpSessionBindingEvent event) => 修改屬性– attributeRemoved(HttpSessionBindingEvent event) => 刪除屬性

實現以上所有的Listener

這裡提供實現這些Listener的範例，因為實在想不出好的實際應用，就分享空的類別原始碼供需要的人參考。

Context監聽器：ServletContextListener, ServletContextAttributeListener

package stockmarket.jovepater.com.stockmarket.Listener;

import javax.servlet.ServletContext;

import javax.servlet.ServletContextAttributeEvent;

import javax.servlet.ServletContextAttributeListener;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import org.springframework.stereotype.Component;

@Component

public class ContextListener implements ServletContextListener, ServletContextAttributeListener {

@Override

public void contextInitialized(ServletContextEvent sce) {

// TODO Auto-generated method stub

ServletContextListener.super.contextInitialized(sce);

System.out.println("ServletContextListener: Context Initialized");

}

ServletContext servletContext;

@Override

public void attributeAdded(ServletContextAttributeEvent scae) {

// TODO Auto-generated method stub

ServletContextAttributeListener.super.attributeAdded(scae);

System.out.println("ServletContextAttributeListener: Context Attribute Added");

}

@Override

public void attributeRemoved(ServletContextAttributeEvent scae) {

// TODO Auto-generated method stub

ServletContextAttributeListener.super.attributeRemoved(scae);

System.out.println("ServletContextAttributeListener: Context Attribute Removed");

}

@Override

public void attributeReplaced(ServletContextAttributeEvent scae) {

// TODO Auto-generated method stub

ServletContextAttributeListener.super.attributeReplaced(scae);

System.out.println("ServletContextAttributeListener: Context Attribute Replaced");

}

@Override

public void contextDestroyed(ServletContextEvent sce) {

// TODO Auto-generated method stub

ServletContextListener.super.contextDestroyed(sce);

System.out.println("ServletContextListener: Context Destroyed");

}

}

Request監聽器：ServletRequestListener, ServletRequestAttributeListener

package stockmarket.jovepater.com.stockmarket.Listener;

import javax.servlet.ServletRequestAttributeEvent;

import javax.servlet.ServletRequestAttributeListener;

import javax.servlet.ServletRequestEvent;

import javax.servlet.ServletRequestListener;

import org.springframework.stereotype.Component;

@Component

public class RequestListener implements ServletRequestListener, ServletRequestAttributeListener {

@Override

public void requestInitialized(ServletRequestEvent sre) {

// TODO Auto-generated method stub

ServletRequestListener.super.requestInitialized(sre);

System.out.println("ServletRequestListener: Request Initialized");

}

@Override

public void attributeAdded(ServletRequestAttributeEvent srae) {

// TODO Auto-generated method stub

ServletRequestAttributeListener.super.attributeAdded(srae);

System.out.println("ServletRequestAttributeListener: Request Attribute Added");

}

@Override

public void attributeRemoved(ServletRequestAttributeEvent srae) {

// TODO Auto-generated method stub

ServletRequestAttributeListener.super.attributeRemoved(srae);

System.out.println("ServletRequestAttributeListener: Request Attribute Removed");

}

@Override

public void attributeReplaced(ServletRequestAttributeEvent srae) {

// TODO Auto-generated method stub

ServletRequestAttributeListener.super.attributeReplaced(srae);

System.out.println("ServletRequestAttributeListener: Request Attribute Replaced");

}

@Override

public void requestDestroyed(ServletRequestEvent sre) {

// TODO Auto-generated method stub

ServletRequestListener.super.requestDestroyed(sre);

System.out.println("ServletRequestListener: Request Destroyed");

}

}

Session監聽器：HttpSessionListener, HttpSessionAttributeListener

package stockmarket.jovepater.com.stockmarket.Listener;

import javax.servlet.http.HttpSessionAttributeListener;

import javax.servlet.http.HttpSessionBindingEvent;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSessionListener;

import org.springframework.stereotype.Component;

@Component

public class SessionListener implements HttpSessionListener, HttpSessionAttributeListener {

@Override

public void sessionCreated(HttpSessionEvent se) {

// TODO Auto-generated method stub

HttpSessionListener.super.sessionCreated(se);

System.out.println("HttpSessionListener: Session Created");

}

@Override

public void attributeAdded(HttpSessionBindingEvent se) {

// TODO Auto-generated method stub

HttpSessionAttributeListener.super.attributeAdded(se);

System.out.println("HttpSessionAttributeListener: Session Attribute Added");

}

@Override

public void attributeRemoved(HttpSessionBindingEvent se) {

// TODO Auto-generated method stub

HttpSessionAttributeListener.super.attributeRemoved(se);

System.out.println("HttpSessionAttributeListener: Session Attribute Removed");

}

@Override

public void attributeReplaced(HttpSessionBindingEvent se) {

// TODO Auto-generated method stub

HttpSessionAttributeListener.super.attributeReplaced(se);

System.out.println("HttpSessionAttributeListener: Session Attribute Replaced");

}

@Override

public void sessionDestroyed(HttpSessionEvent se) {

// TODO Auto-generated method stub

HttpSessionListener.super.sessionDestroyed(se);

System.out.println("HttpSessionListener: Session Destroyed");

}

}

~ END ~

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Context, Listener, Request, Session, Spring Boot