第一次接触servlet的知识

什么是Servlet?
① Servlet就是JAVA 类
② Servlet是一个继承HttpServlet类的类
③　这个在服务器端运行，用以处理客户端的请求
Servlet相关包的介绍
--javax.servlet.* ：存放与HTTP 协议无关的一般性Servlet 类；
--javax.servlet.http.* ：除了继承javax.servlet.* 之外，并且还增加与HTTP协议有关的功能。
　　（注意：大家有必要学习一下HTTP协议，因为ＷＥＢ开发都会涉及到）
　　所有的Servlet 都必须实现javax.servlet.Servlet 接口(Interface)。
　　若Servlet程序和HTTP 协议无关，那么必须继承javax.servlet.GenericServlet类；
　　若Servlet程序和HTTP 协议有关，那么必须继承javax.servlet.http.HttpServlet 类。
--HttpServlet ：提供了一个抽象类用来创建Http Servlet。
　　public void doGet()方法：用来处理客户端发出的 GET 请求
　　public void doPost()方法：用来处理 POST请求
　　还有几个方法大家自己去查阅API帮助文件
--javax.servlet包的接口：
　　ServletConfig接口：在初始化的过程中由Servlet容器使用
　　ServletContext接口：定义Servlet用于获取来自其容器的信息的方法
　　ServletRequest接口：向服务器请求信息
　　ServletResponse接口：响应客户端请求
　　Filter接口：
--javax.servlet包的类：
　　ServletInputStream类：用于从客户端读取二进制数据
　　ServletOutputStream类：用于将二进制数据发送到客户端
--javax.servlet.http包的接口：
　　HttpServletRequest接口：提供Http请求信息
　　HttpServletResponse接口：提供Http响应
Servlet生命周期
--Servlet生命周期就是指创建Servlet实例后，存在的时间以及何时销毁的整个过程．
--Servlet生命周期有三个方法
　　init()方法：
　　service()方法：Dispatches client requests to the protected service method　
　　destroy()方法：Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.
--Servlet生命周期的各个阶段
　　----实例化：Servlet容器创建Servlet实例
　　----初始化：调用init()方法
　　----服务：如果有请求，调用service()方法
　　----销毁：销毁实例前调用destroy()方法
　　----垃圾收集：销毁实例

Servlet的基本结构

package web01;

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 FristServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public FristServlet() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		System.out.println("销毁了servlet！");
	}

	/**
	 * 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 {
		doPost(request, response);//调用doPost
	}

	/**
	 * 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 {

		response.setContentType("text/html");
		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.print("    This is ");
		out.print(this.getClass());
		out.println(", using the POST method");
		out.println("<br/>");
		out.println("<hr/>");
		out.println("<h1>Hello world!</h1>");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
		System.out.println("我是做初始化工作的！");
	}

}

5. Servlet的部署

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name></display-name>
  <servlet>
    <servlet-name>FristServlet</servlet-name>
    <servlet-class>web01.FristServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>FristServlet</servlet-name>
    <url-pattern>/servlet/FristServlet</url-pattern>
  </servlet-mapping>	
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

【注意】

　　①　上面的两个<servlet-name>必须相同
　　②　<servlet-class>后面指在对应的类上面．　　技巧：你可以直接在你的servlet类中复制过来，这样可以避免出错！
　　③　<url-pattern>　必须是/servlet 再加servlet名字.大家现在就这么记.

6.Servlet实例演示

package mybao;

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;

import bean.User;

public class OrderServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public OrderServlet() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		System.out.println("我是init()方法！用来进行初始化工作");
	}

	/**
	 * 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 {

		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.print("    This is ");
		out.print(this.getClass());
		out.println(", using the GET method");
		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 {
		// 设置响应给用户的内容类型和字符集
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out = response.getWriter();

		// 使用表单元素的name属性获取用户输入的表单数据
		String userName = request.getParameter("username");
		String password = request.getParameter("pwd");

		User user = new User();
		user.setUserName(userName);
		user.setPassword(password);

		//request.setAttribute("ukey", user);

		if (userName.equals("admin") && password.equals("123456")) {
			// 请求分发器实现页面转发
			request.getRequestDispatcher("success.jsp").forward(request,response);
		} else {
			// 请求重定向实现页面转向
			response.sendRedirect("failure.jsp"); // 使用相对路径
		}
		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 * 
	 * @throws ServletException
	 *             if an error occurs
	 */
	public void init() throws ServletException {
		System.out.println("我是destroy()方法！用来进行销毁实例的工作");
		// Put your code here
	}

}


web.xml文件
 <servlet>
    <servlet-name>OrderServlet</servlet-name>
    <servlet-class>mybao.OrderServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>OrderServlet</servlet-name>
    <url-pattern>/OrderServlet</url-pattern>
  </servlet-mapping>    
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>

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原文地址：https://www.cnblogs.com/lixiaopan/p/6182496.html