本文共 2918 字，大约阅读时间需要 9 分钟。

首先创建一个验证码

<%@ page contentType="image/jpeg; charset=utf-8" 		language="java" import="java.util.*,java.awt.*,java.awt.image.*,javax.imageio.*"		pageEncoding="UTF-8"%>
   <%!		//获取随机颜色		public Color getColor(){			Random random = new Random();			//使用rgb()随机产生颜色			int r = random.nextInt(256);			int g = random.nextInt(256);			int b = random.nextInt(256);						return new Color(r,g,b);		}				//获取随机数字  产生一个4位数		public String getNum(){			String str = "";			Random random = new Random();			for(int i = 0;i < 4;i++){				str += random.nextInt(10); //0-9			}			return str;		}%><%	 	/* 清除缓存 */	 	response.setHeader("pragma", "mo-cache");		response.setHeader("cache-control", "no-cache");		response.setDateHeader("expires", 0);		//产生矩形框		BufferedImage image = new BufferedImage(80,30,BufferedImage.TYPE_INT_RGB);		//获取画笔工具		Graphics g = image.getGraphics();		//设置矩形框的颜色		g.setColor(new Color(200,200,200));		//设置坐标和宽高		g.fillRect(0, 0, 80, 30);			 			//随机产生干扰线		for(int i = 0;i < 30;i++){			Random random = new Random();			int x = random.nextInt(80);			int y = random.nextInt(30);			int x1 = random.nextInt(x + 10);			int y1 = random.nextInt(y + 10);			//设置随机颜色			g.setColor(getColor());			//画出来			g.drawLine(x, y, x1, y1);		}				//字的颜色和数字		g.setFont(new Font("Microsoft YaHei",Font.BOLD,16));		g.setColor(Color.BLACK);		//获取随机数字		String checkNum = getNum();				//给字拼接空格		StringBuffer sb = new StringBuffer();		for(int i = 0;i < checkNum.length();i++){			sb.append(checkNum.charAt(i) + " ");		}		//画出数字		g.drawString(sb.toString(), 15, 20);		//存入session域中		session.setAttribute("CHECKNUM", checkNum); //例如1010		//将图像以jpeg的形式通过字节流输出		ImageIO.write(image, "jpeg", response.getOutputStream());		//清除缓存		out.clear();		//放入body中		out = pageContext.pushBody();%>

将验证码压缩成图片，在checkcode.jsp中引用,并在该页面中利用ajax向服务器发送数据

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

public class CheckcodeServlet extends HttpServlet {	@Override	protected void doPost(HttpServletRequest req, HttpServletResponse resp)			throws ServletException, IOException {		req.setCharacterEncoding("utf-8");		resp.setContentType("text/html;charset=utf-8");		//图片路径		String tip = "images/MsgError.gif";				String checkcode = req.getParameter("checkcode");		//测试		System.out.println(checkcode);		//获取session域中的数字		String checkcodeService = (String) req.getSession().getAttribute("CHECKNUM");		//判断		if (checkcode.equals(checkcodeService)) {			tip = "images/MsgSent.gif";		}		//输出路径		PrintWriter pw = resp.getWriter();		pw.write(tip);		pw.flush();		pw.close();	}}

运行结果: