简单验证码的实现

验证码：

<%@page import="java.awt.Font"%>
<%@page import="javax.imageio.ImageIO"%>
<%@page import="java.awt.Graphics"%>
<%@page import="java.awt.image.BufferedImage"%>
<%@page import="java.util.Random"%>
<%@page import="java.awt.Color"%>
<%@ page language="java" contentType="image/jpeg; charset=UTF-8" pageEncoding="UTF-8"%>

<%!
	//随机产生颜色值
	public Color getColor(){
		
		//产生r g b 的随机值
		Random random = new Random();
		int r = random.nextInt(256);
		int g = random.nextInt(256);
		int b = random.nextInt(256);
	
		return new Color(r,g,b);//red   green blue  0-255 
	
	}
	//产生随机四位数（真实的验证码值）
	public String getNum(){
		//Math.Random  取值在(0-1) *9000:(0-9000)->0-8999  +1000:(1000-9999) 
		int num = (int)(Math.random()*9000)+1000;
		//转字符串
		return String.valueOf(num);
	}

%>

<%

		//禁止缓存,防止验证码过期
		response.setHeader("Pragma", "no-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setHeader("Expires", "0");
		
		/*
		*绘制验证码
		*/
		BufferedImage  image = new BufferedImage(80,30,BufferedImage.TYPE_INT_RGB);//绘制背景的长宽高
		//画笔
		Graphics graphics = image.getGraphics();
		graphics.fillRect(0, 0, 80, 30);//填充长方形背景
		
		
		
		
		
		
		//设置验证码数字的字体
		graphics.setFont(new Font("seif",Font.BOLD,18));
		
		graphics.setColor(getColor());//绘制验证码的画笔的颜色
		String checkCode = getNum();//验证码的随机数字
		StringBuffer sb = new StringBuffer();
		
		for(int i=0;i<checkCode.length();i++){//checkCode.charAt提取验证码，sb.append拼接空格将其分开
			
			sb.append(checkCode.charAt(i)+" ");
		}
		//验证码数字
		graphics.drawString(sb.toString(), 10,20);//绘制
	
		//绘制干扰线条
				for(int i=0;i<=20;i++){
					
					Random random = new Random();
					
					int xBegin = random.nextInt(80);
					int yBegin = random.nextInt(30);
					int xEnd = random.nextInt(xBegin+10);
					int yEnd = random.nextInt(yBegin+10);
					
					graphics.setColor(getColor());//绘制扰线条的画笔的颜色
					
					graphics.drawLine(xBegin, yBegin, xEnd, yEnd);//绘制线条
				}
		
		//将验证码的真实值放到Session中 供在使用时校验
		session.setAttribute("checkCode", checkCode);
		
		ImageIO.write(image, "jpeg", response.getOutputStream());//真实产生图片
		
		//关闭
		out.clear();
		out = pageContext.pushBody(); // 变成路径  <input type="image" src="xxx" >
		
		
		
 %>

client:

<script type="text/javascript" src="js/jquery-3.1.1.js"></script>
<script type="text/javascript">

	function reloadChekImg(){
			 $("img").attr("src","img.jsp?t="+(new Date().getTime()));
		}	



	$(document).ready(function(){
		$("#checkCodeId").blur(function(){
				
				//校验：文本框中输入的值 发送到服务器
				//服务器： 校验文本框的值 与真是图片的验证码的值 是否相等
				var $checkCode = $("#checkCodeId").val();
						$.post(
							"checkServlet",
							"checkCode="+$checkCode,
							function(data){//返回图片地址   imgs/right.jpg   imgs/wrong.jpg
									var $dataContent = $("<img src='"+data+"' height='15px' width='15px' />")
									if(data == "imgs/wrong.jpg"){
										$("img").attr("src","img.jsp?t="+(new Date().getTime()));
										}
									$("#tip").html($dataContent);
								}
						);
			
			})	;

		});


</script>

验证码： ``` ***Server***

//返回值
		String dataTip = "imgs/wrong.jpg";
		//获取用户敲得验证码值
		String checkcodeClient = request.getParameter("checkCode");
		//获取真实的验证码值
		String checkcodeServer = (String) request.getSession().getAttribute("checkCode");
		
		if(checkcodeClient .equals(checkcodeServer )) {//判断两者是否相等
			dataTip = "imgs/right.jpg" ;
		}
		response.setContentType("text/html; charset=UTF-8");
		PrintWriter out = response.getWriter();
		out.write(dataTip);
		out.flush();//刷新
		out.close();