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本人亲写亲测，解决了jsp生成的验证码图片和session不同步的问题。两者不同步是因为jsp先加载html代码，然后才

image.jsp------------------------------生成随机验证码图片的Jsp页面

代码如下： 

<%@page import="javax.imageio.ImageIO"%>  <%@page import="java.awt.Font"%>  <%@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"%>  <%!      //获取随机颜色      Color getRandColor(int fc,int bc){      Random random = new Random();      if(fc>255) fc=255;      if(bc>255) bc=255;      int r = fc + random.nextInt(bc - fc);      int g = fc + random.nextInt(bc - fc);      int b = fc + random.nextInt(bc - fc);      return new Color(r,g,b);      }  %>  <%      //设置页面不缓存       response.setHeader("Pragma", "No-cache");      response.setHeader("Cache-Control", "no-cache");         response.setDateHeader("Expires", 0);      //在内存中创建图像      int width = 60;      int height = 20;      BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);      //获取图形上下文      Graphics g = image.getGraphics();      //随机类      Random random = new Random();      //设定背景      g.setColor(getRandColor(200, 250));      g.fillRect(0, 0, width, height);      //设定字体      g.setFont(new Font("Times New Roman",Font.PLAIN,18));     //随机产生干扰线     g.setColor(getRandColor(160, 200));        for (int i = 0; i < 100; i++) {             int x = random.nextInt(width);             int y = random.nextInt(height);             int xl = random.nextInt(12);             int yl = random.nextInt(12);             g.drawLine(x, y, x + xl, y + yl);        }      //随机产生4位验证码     String[] codes = {"2","3","4","5","6","7","8","9","A","B","C","D","E","F","G","H","J","K","L","M","N","P","Q","R","S","T","U","V","W","X","Y","Z"};     String code = "";     for(int i=0;i<4;i++){         String str = codes[random.nextInt(codes.length)];         code += str;         // 将认证码显示到图象中         g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));         //调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成            g.drawString(str, 13 * i + 6, 16);        }      // 将认证码存入SESSION        session.setAttribute("code", code);     // 图象生效        g.dispose();        // 输出图象到页面        ImageIO.write(image, "JPEG", response.getOutputStream());     //加上下面代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has already been called ..........等异常     response.getOutputStream().flush();       response.getOutputStream().close();       response.flushBuffer();       out.clear();       out = pageContext.pushBody();   %>

logic.jsp--------------------------------登陆页面，在这里提供输入验证码然后提交并验证

<%@ page contentType="text/html;charset=UTF-8" %>
   
   
   
        
     
                  
           
       
                                      
         
           
 
           
             
             
               
用户名：
               
 
               
 
              
              
               
密   码：
               
 
               
 
              
              
               
验证码：
               
 
               
 
              
             
           
 
          
          
           
 
           
             
             
               
               
 
                  记住密码 
               
 
               
              
             
           
 
          
         
       
       
                   
    
   

后台验证登录Controller如下：--------------------------用来验证输入的验证码是否正确及用户名和密码信息。

public class LoginoaController {    //.....	public ModelAndView validate(HttpServletRequest request, HttpServletResponse response) throws IOException {		String userName = request.getParameter("loginId");		String password = request.getParameter("password");		String code = request.getParameter("code");        //下面是关键，必须使用session		 HttpSession session = request.getSession();	    String checkCode_session = (String) session.getAttribute("code");	        //删除session中存储的验证码	     session.removeAttribute("checkCode_session");	     		if(!code.equals(checkCode_session)){                 String str = "{\"info\":\"验证码错误\",\"success\":true,\"sroleType\":false,\"code\":-3}";				super.outJson(str.toString(), response);    //验证结果返回前台			}else{				//用户名和密码验证				}		return null;	}}

前两个jsp和WEB-INF同级目录下，如果你放在不同的文件夹下，那么里面相关页面的路径自己稍作更改就可以了。

以上为本次前台验证码的主要功能代码。验证码判断是无法在jsp登录页面直接判断获取的，必须经过一个servlet转换。

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