Tomcat装载Servlet的三种情况 博客分类： java TomcatServlet
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2024-03-18 16:31:28
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一 时刻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
<loadon-startup>1</loadon-startup>
数字越小表示优先级别越高。
1 关键代码
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
<display-name></display-name>
<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>
<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-mapping>
<servlet-name>TestServlet1</servlet-name>
<url-pattern>/servlet/TestServlet1</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>TestServlet2</servlet-name>
<url-pattern>/servlet/TestServlet2</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
2 测试
TestServlet2构造方法被执行....
TestServlet2的初始化方法被执行....
TestServlet1构造方法被执行....
TestServlet1的初始化方法被执行....
二 时刻2
在Servlet容器启动后，客户首次向Servlet发送请求。
1 关键代码
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() {
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的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的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 {
// Put your code here
System.out.println("TestServlet1的初始化方法被执行....");
}
}
2 测试
TestServlet1构造方法被执行....
TestServlet1的初始化方法被执行....
TestServlet1的doGet()方法被执行...
九月 24, 2017 2:51:01 下午 org.apache.catalina.core.StandardServer await
信息: A valid shutdown command was received via the shutdown port. Stopping the Server instance.
九月 24, 2017 2:51:01 下午 org.apache.coyote.AbstractProtocol pause
信息: Pausing ProtocolHandler ["http-apr-8888"]
九月 24, 2017 2:51:01 下午 org.apache.coyote.AbstractProtocol pause
信息: Pausing ProtocolHandler ["ajp-apr-8009"]
九月 24, 2017 2:51:01 下午 org.apache.catalina.core.StandardService stopInternal
信息: Stopping service Catalina
九月 24, 2017 2:51:02 下午 org.apache.catalina.core.ApplicationContext log
信息: SessionListener: contextDestroyed()
九月 24, 2017 2:51:02 下午 org.apache.catalina.core.ApplicationContext log
信息: ContextListener: contextDestroyed()
TestServlet1销毁方法被执行....
三 时刻3
Servlet类文件被更新后，重新装载Servlet。
修改文件后，生成类文件时间发生变化
四 说明
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，init()方法只被调用一次。
