Servlet生命周期

最新推荐文章于 2025-09-06 09:33:29 发布

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原文链接：http://www.cnblogs.com/sdut-myj/p/4340047.html

文章标签：

#java #web.xml

在下列时刻Servlet容器装载Servlet:
1.Servlet容器启动时自动装载某些Servlet,实现它只需要在web.xml文件中的<Servlet></Servlet>之间添加如下代码：
<load-on-startup>1</load-on-startup> 数字越小表示优先级越高。
2.在Servlet容器启动后，客户端首次向Servlet发送请求。
3.Servlet类文件被更新后，重新装载Servlet。

第一种情况：

Servlet被装载后，Servlet容器创建一个Servlet实例并且调用Servlet的init()方法进行初始化。在Servlet的整个生命周期内，init()方法只被调用一次。

package Servlet;

import java.io.IOException;
import java.io.PrintWriter;

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

public class TestServlet1 extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public TestServlet1() {
		System.out.println("TestServlet1构造方法被执行...");
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		System.out.println("TestServlet1销毁方法被执行...");
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		System.out.println("TestServlet1 doGet()方法被执行...");
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();
		out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.println("<h1>大家好，我是TestServlet1</h1>");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		System.out.println("TestServlet1 doPost()方法被执行...");
		doGet(request,response);//让doPost()执行与doGet()相同的操作。
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		System.out.println("TestServlet1初始化方法被执行...");
	}

}

　　web.xml代码：

 <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>TestServlet1</servlet-name>
    <servlet-class>Servlet.TestServlet1</servlet-class>
  </servlet>
<servlet-mapping>
    <servlet-name>TestServlet1</servlet-name>
    <url-pattern>/servlet/TestServlet1</url-pattern>
  </servlet-mapping>

　　index.jsp代码：

 <body>
  <h1>Servlet生命周期</h1>
  <hr>
  <a href="servlet/TestServlet1">以get方式请求TestServlet1</a>
  
  </body>

　　运行结果：

第二种：

怎么让Servlet容器启动时自动装载某些Servlet?
答：需要在web.xml文件中进行如下配置：
<servlet>
....
<load-on-startup>1</load-on-startup>
</servlet>

代码：

 <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>TestServlet2</servlet-name>
    <servlet-class>Servlet.TestServlet2</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>TestServlet1</servlet-name>
    <servlet-class>Servlet.TestServlet1</servlet-class>
   <load-on-startup>2</load-on-startup>
  </servlet>