Servlet生命周期
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>
