servlet生命周期

 同人的生老病死，servlet也有生命周期，其收到web容器的控制，其生命周期包括 加载程序，初始化、服务、销毁、卸载5个部分，如下图所示;



代码验证：

自定义LifeCycleServlet继承HttpServlet，覆写其生命周期相应方法

package helloservlet;

import java.io.IOException;

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

public class LifeCycleServlet extends HttpServlet {
/**
*
*/
private static final long serialVersionUID = -1922315362237286875L;

@Override
public void init() throws ServletException {
System.out.println("** 1、Servlet初始化 --> init()");
}

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println("** 2、Servlet服务 --> doGet()、doPost()");
}

@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
this.doPost(req, resp);
}

@Override
public void destroy() {
System.out.println("** 3、Servlet销毁 --> destory()");
try {
Thread.sleep(30000);
} catch (Exception e) {
}
}

}

在web.xml中配置：

<servlet>
<servlet-name>life</servlet-name>
<servlet-class>helloservlet.LifeCycleServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>life</servlet-name>
<url-pattern>/LifeServlet</url-pattern>
</servlet-mapping>

运行观察：



容器tomcat关掉，调用destory( )方法

如果在配置文件中加入：

<load-on-startup>1</load-on-startup>

配置:

<servlet>
<servlet-name>life</servlet-name>
<servlet-class>helloservlet.LifeCycleServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>life</servlet-name>
<url-pattern>/LifeServlet</url-pattern>
</servlet-mapping>

容器tomcat启动时就会自动为sevlet初始化：



实际应用时，不会覆写生命周期的全部方法，依需求，需要哪个覆写哪个，doGet（），doPost（）使用几率最高，主要覆写这两个