Java Servlet 实战-优快云博客

本文链接：https://blog.youkuaiyun.com/haha258258/article/details/51441620

本文介绍 Java Servlet 的概念及其发展背景，并通过一个简单的增删改查示例演示如何使用 Servlet 处理前端请求。

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为什么想写这个?

突然兴起,想研究研究servelt

servlet是什么?

servlet=server+applet(小服务),全程 java servlet,是用java语言编写的服务端程序.主要功能就是为前端的请求提供服务(官方描述是:交互式地浏览和修改数据,生成动态web内容),

狭义的servlet是java语言实现的一个接口,广义的servlet是任何实现这个servlet接口的类.

servlet出现背景?

简单来说是为了完成客户端和服务端的数据交互.

事情的经过其实是这样的,一开始,实现数据交互是通过编写CGI(通用网关接口),但是CGI方式的运行要开启多个进程,速度慢,效率低,相当消耗系统资源,因此出现了用多线程代替多进程的方式来解决这个数据交互问题,这就是servlet

servlet demo

运用servet实现增删改查,

index.jsp:操作页面.

ok.jsp:成功页面

UserServlet:处理类

web.xml:配置servlet的映射

代码:

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
  </head>
  
  <body>
    servlet 增 删 改 查 <br>
     <form action="userServlet" method="post">
    	<input type="submit" value="增"></input>
    	<input type="hidden" type="method" name="method"   value="add">
    </form><br>
     <form action="userServlet" method="post">
    	<input type="submit" value="删"></input>
    	<input type="hidden" name="method"  value="del">
    </form><br>
     <form action="userServlet" method="post">
    	<input type="submit" value="改"></input>
    	<input type="hidden" name="method"  value="modify">
    </form><br>
     <form action="userServlet" method="post">
    	<input type="submit" value="查"></input>
    	<input type="hidden" name="method"  value="select">
    </form><br>
  </body>
</html>

ok.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'ok.jsp' starting page</title>
    
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

  </head>
  
  <body>
    ok <br>
  </body>
</html>

UserServlet.java

import java.io.IOException;

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


public class UserServlet implements Servlet {

	public void destroy() {
		// TODO Auto-generated method stub
		
	}

	public ServletConfig getServletConfig() {
		// TODO Auto-generated method stub
		return null;
	}

	public String getServletInfo() {
		// TODO Auto-generated method stub
		return null;
	}

	public void init(ServletConfig config) throws ServletException {
		// TODO Auto-generated method stub
		
	}

	public void service(ServletRequest req, ServletResponse res)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		String method=(String)req.getParameter("method");
		RequestDispatcher rd=req.getRequestDispatcher("ok.jsp");
		if("add".equals(method)){
			System.out.println("增");
			rd.forward(req, res);
		}
		if("del".equals(method)){
			System.out.println("删");
			rd.forward(req, res);
		}
		if("modify".equals(method)){
			System.out.println("改");
			rd.forward(req, res);
		}
		if("select".equals(method)){
			System.out.println("查");
			rd.forward(req, res);
		}
		
	}

	
	
	

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
    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_2_5.xsd">
  <display-name></display-name>    
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
      <servlet-name>userServlet</servlet-name>
      <servlet-class>UserServlet</servlet-class>
  </servlet>
  
  <servlet-mapping>
      <servlet-name>userServlet</servlet-name>
      <url-pattern>/userServlet</url-pattern>
  </servlet-mapping>
</web-app>