Spring Boot EP 14：使用Listener監聽器管理Context、Request與Session的生命週期
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 |
| Context | ServletContextListener | ServletContextAttributeListener |
| Request | ServletRequestListener | ServletRequestAttributeListener |
| Session | HttpSessionListener | HttpSessionAttributeListener |
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 ~
