Javaweb之Servlet入门

1. 什么是Servlet?

Java Servlet 是运行在 Web 服务器或应用服务器上的程序；他是浏览器（HTTP客户端）请求和HTTP服务器上资源（访问数据库）之间的中间层。

2. 什么是Servlet的运行环境？

Servlet容器是Java Servlet程序的运行环境，比如，常用的tomcat，同时它也是web服务器；

3. 什么是Servlet的生命周期？

Servlet的创建到销毁的过程称为Servlet的生命周期；具体分为三个阶段：

• Servlet初期化 init()
• Servlet处理请求 service()
• Servlet销毁 destroy()

4. 创建一个Servlet示例程序

package com.cjt.servlet;

import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class HellowordServlet
 */
@WebServlet(description = "Servlet示例", urlPatterns = { "/helloworld" })
public class HellowordServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public HellowordServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see Servlet#init(ServletConfig)
	 */
	public void init(ServletConfig config) throws ServletException {
		// TODO Auto-generated method stub
		System.out.println("Servlet初期化");
	}

	/**
	 * @see Servlet#destroy()
	 */
	public void destroy() {
		// TODO Auto-generated method stub
		System.out.println("Servlet销毁");
	}

	/**
	 * @see HttpServlet#service(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		System.out.println("Servlet处理请求");
		response.getWriter().println("你好，这是来自Servlet的消息：Hello World!");
	}
}

web.xml

<?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>ServletHello</display-name>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

注：Servlet3.0支持注解