一、新建Web项目，新建一个Servlet，取名：YZM.java
注意：验证码里面设置了Session的名字以及它的值
在WEB.xml里面对这个Servlet进行申明:
<servlet>
<servlet-name>YZM</servlet-name>
<servlet-class>YZM</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>YZM</servlet-name>
<url-pattern>/YZM</url-pattern>
</servlet-mapping>
1 import java.awt.Color; 2 import java.awt.Font; 3 import java.awt.Graphics; 4 import java.awt.image.BufferedImage; 5 import java.io.IOException; 6 import java.util.Random; 7 import javax.imageio.ImageIO; 8 import javax.servlet.ServletException; 9 import javax.servlet.annotation.WebServlet; 10 import javax.servlet.http.HttpServlet; 11 import javax.servlet.http.HttpServletRequest; 12 import javax.servlet.http.HttpServletResponse; 13 import javax.servlet.http.HttpSession; 14 @WebServlet("/YZM") 15 public class YZM extends HttpServlet { 16 private static final String CONTENT_TYPE = "text/html; charset=utf-8"; 17 18 //设置字母的大小,大小 19 private Font mFont = new Font("Arial", Font.BOLD, 18); 20 public void init() throws ServletException 21 { 22 super.init(); 23 } 24 25 //去随机颜色 26 Color getRandColor(int fc,int bc) 27 { 28 Random random = new Random(); 29 if(fc>255) fc=255; 30 if(bc>255) bc=255; 31 int r=fc+random.nextInt(bc-fc); 32 int g=fc+random.nextInt(bc-fc); 33 int b=fc+random.nextInt(bc-fc); 34 return new Color(r,g,b); 35 } 36 37 public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 38 { 39 response.setHeader("Pragma","No-cache"); 40 response.setHeader("Cache-Control","no-cache"); 41 response.setDateHeader("Expires", 0); 42 //表明生成的响应是图片 43 response.setContentType("image/jpeg"); 44 45 int width=80, height=18; 46 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); 47 48 Graphics g = image.getGraphics(); 49 Random random = new Random(); 50 g.setColor(getRandColor(200,250)); 51 g.fillRect(1, 1, width-1, height-1); 52 g.setColor(new Color(102,102,102)); 53 g.drawRect(0, 0, width-1, height-1); 54 g.setFont(mFont); 55 g.setColor(getRandColor(160,200)); 56 57 //画随机线 58 for (int i=0;i<155;i++) 59 { 60 int x = random.nextInt(width - 1); 61 int y = random.nextInt(height - 1); 62 int xl = random.nextInt(6) + 1; 63 int yl = random.nextInt(12) + 1; 64 g.drawLine(x,y,x + xl,y + yl); 65 } 66 67 //从另一方向画随机线 68 for (int i = 0;i < 70;i++) 69 { 70 int x = random.nextInt(width - 1); 71 int y = random.nextInt(height - 1); 72 int xl = random.nextInt(12) + 1; 73 int yl = random.nextInt(6) + 1; 74 g.drawLine(x,y,x - xl,y - yl); 75 } 76 77 //生成随机数,并将随机数字转换为字母 78 String sRand=""; 79 for (int i=0;i<4;i++) 80 { 81 int itmp = random.nextInt(26) + 65; 82 char ctmp = (char)itmp; 83 sRand += String.valueOf(ctmp); 84 g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110))); 85 g.drawString(String.valueOf(ctmp),15*i+10,16); 86 } 87 88 HttpSession session = request.getSession(true); 89 //把放入Seession的值改成小写 90 sRand = sRand.toLowerCase(); 91 92 session.setAttribute("rand",sRand); 93 g.dispose(); 94 ImageIO.write(image, "JPEG", response.getOutputStream()); 95 } 96 }
二、新建一个JSP文件，index.jsp
着重注意：第11行如何对刚才创建的验证码图片进行引用，
title="点击刷新" 作用：鼠标移到上面会现实提示
style=cursor:pointer 作用：鼠标移到上面改变鼠标的图标
onclick="this.src=this.src" 作用：可实现点击刷新
1 <%@ page language="java" contentType="text/html; charset=UTF-8" 2 pageEncoding="UTF-8"%> 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 4 <html> 5 <head> 6 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 7 <title>Insert title here</title> 8 </head> 9 <body> 10 <!-- 引用验证码 --> 11 <img title="点击刷新" style=cursor:pointer onclick="this.src=this.src" src="YZM"/> 12 13 <!-- 简单的一个表单，测试下验证码 --> 14 <form action="checkLogin" method="post"> 15 <input type="text" name="yzm"/> 16 <input type="submit" value="提交"/> 17 </form> 18 </body> 19 </html>
三、再创建一个Servlet对表单里输入的验证码进行判断
在WEB.xml里面对这个Servlet进行申明:
<servlet>
<servlet-name>checkLogin</servlet-name>
<servlet-class>checkLogin</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>checkLogin</servlet-name>
<url-pattern>/checkLogin</url-pattern>
</servlet-mapping>
1 import java.io.IOException; 2 import java.io.PrintWriter; 3 4 import javax.servlet.ServletException; 5 import javax.servlet.annotation.WebServlet; 6 import javax.servlet.http.HttpServlet; 7 import javax.servlet.http.HttpServletRequest; 8 import javax.servlet.http.HttpServletResponse; 9 import javax.servlet.http.HttpSession; 10 11 import org.apache.catalina.connector.Request; 12 13 @WebServlet("/checkLogin") 14 public class checkLogin extends HttpServlet { 15 private static final long serialVersionUID = 1L; 16 17 public checkLogin() { 18 super(); 19 } 20 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 21 response.setContentType("text/html;charset=utf-8"); 22 request.setCharacterEncoding("utf-8"); 23 PrintWriter out = response.getWriter(); 24 25 //获取Session 26 HttpSession yzmSession = request.getSession(); 27 28 //获取用户输入的验证码 29 String yzm = request.getParameter("yzm"); 30 String systemYzm= (String)yzmSession.getAttribute("rand"); 31 32 out.print("systemYzm = " + systemYzm); 33 out.print("\n"); 34 out.print("yzm = " + yzm); 35 out.print("\n"); 36 37 if(systemYzm.equals(yzm)){ 38 out.print("验证码输入正确\n"); 39 }else{ 40 out.print("验证码输入错误\n"); 41 } 42 } 43 44 }
Servlet验证码的生成与使用,布布扣,bubuko.com
原文：http://www.cnblogs.com/jiexiang/p/3600918.html