Servlet的执行过程

Posted 2021-01-23 qf123

一个简单的servlet项目结构

 

web.xml相关配置

 

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
　　xmlns="http://java.sun.com/xml/ns/javaee" 
　　xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
　　http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>HelloServlet</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
  	<servlet-name>hello</servlet-name>
  	<servlet-class>com.qf.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>hello</servlet-name>
  	<url-pattern>/hello</url-pattern>
  </servlet-mapping>
</web-app>

servlet相关代码

package com.qf.servlet;

import java.io.IOException;

import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class HelloServlet implements Servlet {
    @Override
    public void service(ServletRequest arg0, ServletResponse arg1) throws ServletException, IOException {
        System.out.println("helloServlet");
    }
    @Override
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub    
    }
    @Override
    public ServletConfig getServletConfig() {
        // TODO Auto-generated method stub
        return null;
    }
    @Override
    public String getServletInfo() {
        // TODO Auto-generated method stub
        return null;
    }
    @Override
    public void destroy() {
        // TODO Auto-generated method stub  
    }
}

url：http://localhost:8080/HelloServlet/hello

控制台输出结果：

helloServlet

具体执行过程：

1. 找到tomcat应用
2. 找到项目
3. 找到web.xml，在web.xml中找到url-pattern标签的内容能匹配/hello的
4. 找到这个url-pattern对应的servlet-name，进而找到相关servlet-class
5. 创建该servlet-class对应的servlet类的实例
6. 调用service方法进行处理