session绑定的验证码返回的是null

[zhengjianhua7]

else if(action.equals("/login")){
			//number1:用户提交的验证码
			String number1=request.getParameter("number");
			//number2:session对象上绑定的验证码
			HttpSession session=request.getSession();
			String number2=(String)session.getAttribute("number");
			if(!number1.equalsIgnoreCase(number2)){
				request.setAttribute("number_error", "验证码错误");
				request.getRequestDispatcher("login.jsp")
				.forward(request,response);
				return;
			}
			//只有在验证码正确的情况下，才会比较用户名和密码是否正确
			String username = 
		  		request.getParameter("username");
		  	String pwd = 
		  		request.getParameter("pwd");
		  	UserDAO dao = new UserDAO();
		  	try {
	        User user = dao.findByUserName(username);
//	        System.out.println(user.getPwd()+",");
	        try {
				if(user != null && user.getPwd().equals(MD5Util.encrypt(pwd.toUpperCase()))){
					//绑订数据到session对象上，用于验证
					session.setAttribute("user", user);
					//登录成功,跳转到主功能页面
					response.sendRedirect("list.do");
				}else{
					//登录失败,提示用户
					request.setAttribute("login_error", 
							"用户名或密码错误");
					request.getRequestDispatcher("login.jsp")
					.forward(request, response);
				}
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
        } catch (SQLException e) {
	        e.printStackTrace();
	        //将系统异常扔给容器来处理
	        throw new ServletException(e);
        }		
		}

package web;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class CheckcodeServlet extends HttpServlet {
		private int WIDTH= 80;
		private int HEIGHT= 30;
		public void service(HttpServletRequest request, HttpServletResponse response)
	    throws ServletException, IOException {
			//一、绘图
			//step1,创建一个内存映像对象(画布)
			BufferedImage image = 
				new BufferedImage(WIDTH,HEIGHT,
						BufferedImage.TYPE_INT_RGB);
			//step2,获得画笔
			Graphics g = image.getGraphics();
			//step3,
			Random r = new Random();
			//step3,给画笔上一个随机的颜色
			g.setColor(new Color(r.nextInt(255),
					r.nextInt(255),r.nextInt(255)));
			//step4,填充画布
			g.fillRect(0, 0, WIDTH, HEIGHT);
			//step5,在画布上绘图
//			String number = r.nextInt(99999) + "";
			String number ="";
//			g.setColor(new Color(0,0,0));
			for (int i = 0; i < 4; i++) {
				g.setColor(new Color(r.nextInt(255),
				r.nextInt(255),r.nextInt(255)));
				int h=(int)(HEIGHT*0.3+(HEIGHT*0.7)*r.nextDouble());
				g.setFont(new Font(null,Font.ITALIC|Font.BOLD,h));
				String str=getNumber(1);
				number+=str;
				g.drawString(str, i*WIDTH/5, h);
			}
			//将number 绑定到session上
			HttpSession session =request.getSession();
			session.setAttribute("number", number);
			
			//step6,设置字体的大小、风格
//			g.setFont(new Font(null,
//					Font.ITALIC|Font.BOLD,20));
//			g.drawString(number, 5, 22);
			//加干扰线
			for (int i = 0; i < 3; i++) {
				g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255),r.nextInt(255)));
			    g.drawLine(r.nextInt(WIDTH), r.nextInt(HEIGHT),r.nextInt(WIDTH), r.nextInt(HEIGHT));
			}
			//二、压缩图片，输出
			response.setContentType("image/jpeg");
			OutputStream ops = 
				response.getOutputStream();
			//write方法:将原始图片(image)使用
			//指定的压缩算法(jpeg)进行压缩，然后
			//使用指定的输出流(ops)输出。
			ImageIO.write(image, "jpeg",	ops);
			ops.close();
	}/*返回一个指定长度的字符串
	  要求从A~Z，0~9中随机选取字符
	 */
	   
		private String getNumber(int size) {
			Random r=new Random();
			String strs="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
				+"0123456789";
			String number="";
			for (int i = 0; i < size; i++) {
				number+=strs.charAt(r.nextInt(strs.length()));
			}	
			
			return number;		
		}

}

[1057053095]

额，你的验证码是个类文件,你的页面调用CheckcodeServlet这个类没有，让他对session里面的验证码初始化应该就有值了把

[zhengjianhua7]

我在第一个的第六行打印的number2的值是null

java.lang.NullPointerException
	at web.ActionServlet.service(ActionServlet.java:136)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Thread.java:619)

[zhengjianhua7]

求救啊

[Mr_JieLQ]

你可以在CheckcodeServlet 类的47行下面写个打印语句，System.out.println(number);，看看是否给number赋值成功

[snailjumpjump]

你在登录页面能看到验证码吗？如果你登录页面能看到验证码，说明验证码生成成功了，是你放置在session中出问题了，或者在其他的地方将session的清掉了；如果登录页面没看到验证码，说明生成验证码的地方又问题，

[snailjumpjump]

你这个地方写的有问题吧，看的方法，是想String str=getNumber(i)生成字符串，然后拼接的，但是寄传进去的是1，这样的话，str的值一直是空的，拼出来的number也是空的，下次要仔细啊

[zhengjianhua7]

还是生成的验证码是空的

[wyx100]

引用 2 楼 u011564172 的回复:

你可以在CheckcodeServlet 类的47行下面写个打印语句，System.out.println(number);，看看是否给number赋值成功

顶

[scmod]

楼主是不是禁用cookie了?

[zhengjianhua7]

CheckcodeServlet 类的47行下面写个打印语句，System.out.println(“2222222222223”+number)打印的没有在控制台显示，怎么回事

[zhengjianhua7]

自己顶一下。。。

[zhengjianhua7]

断点追踪，程序没有跑到CheckcodeServlet中去

[苹果树9]

我一般是将 生成的验证码后保存到session中。