验证码？

Question

在login.jsp页面里，要显示验证码： </tr>
   <tr><td>验证码:</td><td><input type="text" name="identfiy"></td><td><img src="/servlet/ImageGerator"> <%=session.getAttribute("Login_Image_Code")%></td>
   </tr>
产生验证码的servlet的代码： package com.fuyou.servlet;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.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class ImageGerator extends HttpServlet { private static final long serialVersionUID = 5688443850114813473L; private static 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);
} private static String charsLong = "23456789abcdefghjklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ"; private static String chars = charsLong; public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { int charsLength = chars.length(); response.setHeader("ragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0); int width = 70, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics(); Random random = new Random();
g.setColor(getRandColor(200, 250));//a
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman", Font.ITALIC, height));
g.setColor(getRandColor(160, 200));//b for (int i = 0; i < 35; 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);
}
StringBuilder sRand = new StringBuilder();
String[] fontNames = { "Times New Roman", "Arial", "Book antiqua", "" };
for (int i = 0; i < 4; i++) {
g.setFont(new Font(fontNames[random.nextInt(3)], Font.ITALIC,
height));  //a
char rand = chars.charAt(random.nextInt(charsLength));
sRand.append(rand);
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110)));  //b
g.drawString(String.valueOf(rand), 16 * i + random.nextInt(6) + 3,
height - random.nextInt(4)); }
  g.setColor(getRandColor(160, 200));
for (int i = 0; i < 30; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(width);
int yl = random.nextInt(width);
g.drawLine(x, y, x + xl, y + yl);
}
request.getSession().setAttribute("Login_Image_Code", sRand.toString()); g.dispose();
try {
Thread.sleep(100);
} catch (Exception ex) {
}
RequestDispatcher re = request.getRequestDispatcher("../login.jsp");
re.forward(request, response);
    OutputStream os = response.getOutputStream();
     ImageIO.write(image, "JPEG", os);
  
   
 
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}}我想实现 一登录login.jsp页面，验证码就显示出来？

Answer 1

<tr>
    <td>验证码:</td>
    <td><input type="text" name="identfiy"></td>
    <td><img src="/servlet/ImageGerator"></td>
</tr>修改web.xml增加ImageGerator这个servlet的定义 <servlet>
<servlet-name>ImageGerator</servlet-name>
<display-name>ImageGerator</display-name>
<servlet-class>
com.fuyou.servlet.ImageGerator
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ImageGerator</servlet-name>
<url-pattern>/servlet/ImageGerator</url-pattern>
</servlet-mapping>

Answer 2

一楼的朋友，按你意思 我改了，但还没出来！
web.xml<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" 
xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>ImageGerator</servlet-name>
    <servlet-class>com.fuyou.util.ImageGerator</servlet-class>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>loginservlet</servlet-name>
    <servlet-class>com.fuyou.servlet.loginservlet</servlet-class>
  </servlet><servlet-mapping>
    <servlet-name>ImageGerator</servlet-name>
    <url-pattern>/servlet/ImageGerator</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>loginservlet</servlet-name>
    <url-pattern>/servlet/loginservlet</url-pattern>
  </servlet-mapping>
</web-app>
</tr>
   <tr><td>验证码:</td><td><input type="text" name="identfiy"></td><td><img src="/servlet/ImageGerator"> <%=session.getAttribute("Login_Image_Code")%></td>
   </tr>

Answer 3

just try<tr>
 <td>验证码:</td>
 <td><input type="text" name="identfiy"></td>
 <td><img src="servlet/ImageGerator"></td>
</tr>

Answer 4

有控制台下面的信息：2008-2-29 15:14:34 org.apache.catalina.core.StandardWrapperValve invoke
信息: Servlet ImageGerator is currently unavailable

Answer 5

<img src="/servlet/ImageGerator" onload="getSession()" /><span id="validateNumber" ></span>
<script language="javascript">
   var xhr;
   function getSession(){
       xhr=new ActiveXObject("microsoft.xmlhttp");
       xhr.open "get","servlet/GetSession",true
       xhr.onreadystatechange=functon(){
           if(xhr.readystate==4){
              if(xhr.status==200){
                    document.getElementById("validateNumber").innerHTML=xhr.responseText
              }
           }
       }
       xhr.send(null);
   }
</script>public class GetSession extends HttpServlet{
    ....
    public void doGet(HttpServletRequest,HttpServletResponse) throws IOException,ServletException{
         HttpSession session=request.getSession();
         PrintWriter out=response.getWriter();
         out.println(session.getAttribute("Login_Image_Code").toString());
         out.flush();
         out.close();
    }
}

Answer 6

或者在login.jsp中生成验证字符串，打印出来，在servlet中获取session中的验证字符串，生成图片验证码

Answer 7

<servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>ImageGerator</servlet-name>
    <servlet-class>com.fuyou.util.ImageGerator</servlet-class>
  </servlet>
你的代码写的是 package com.fuyou.servlet;
这里写的是com.fuyou.util.ImageGerator搞毛啊你？

Answer 8

真是失误啊!改过来了，但还是有下面的错误：HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception java.lang.IllegalStateException: getWriter() has already been called for this response
org.apache.catalina.connector.Response.getOutputStream(Response.java:576)
org.apache.catalina.connector.ResponseFacade.getOutputStream(ResponseFacade.java:181)
com.fuyou.servlet.ImageGerator.doGet(ImageGerator.java:96)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.25 logs.
--------------------------------------------------------------------------------Apache Tomcat/5.5.25

Answer 9

getWriter()  在哪里用到了/???????????

Answer 10

生成servlet没有getWriter( ),我仔细看了！
package com.fuyou.servlet;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.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class ImageGerator extends HttpServlet { private static final long serialVersionUID = 5688443850114813473L; private static 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);
} private static String charsLong = "23456789abcdefghjklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ"; private static String chars = charsLong; public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { int charsLength = chars.length(); response.setHeader("ragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0); int width = 70, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics(); Random random = new Random();
g.setColor(getRandColor(200, 250));//a
g.fillRect(0, 0, width, height);
g.setFont(new Font("Times New Roman", Font.ITALIC, height));
g.setColor(getRandColor(160, 200));//b for (int i = 0; i < 35; 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);
}
StringBuilder sRand = new StringBuilder();
String[] fontNames = { "Times New Roman", "Arial", "Book antiqua", "" };
for (int i = 0; i < 4; i++) {
g.setFont(new Font(fontNames[random.nextInt(3)], Font.ITALIC,
height));  
char rand = chars.charAt(random.nextInt(charsLength));
sRand.append(rand);
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110)));  //b
g.drawString(String.valueOf(rand), 16 * i + random.nextInt(6) + 3,
height - random.nextInt(4)); }
  g.setColor(getRandColor(160, 200));
for (int i = 0; i < 30; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(width);
int yl = random.nextInt(width);
g.drawLine(x, y, x + xl, y + yl);
}
request.getSession().setAttribute("Login_Image_Code", sRand.toString());
System.out.println(request.getSession().getAttribute("Login_Image_Code").toString()); g.dispose();
try {
Thread.sleep(100);
} catch (Exception ex) {
}
RequestDispatcher re = request.getRequestDispatcher("/login.jsp");
re.forward(request, response);
    OutputStream os = response.getOutputStream();
    ImageIO.write(image, "JPEG", os);
  
   
 
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
}}

Answer 11

解决方案：在程序的最后添加：
out.clear();
out = pageContext.pushBody(); 
http://internet.blog.enorth.com.cn/article/227796.shtml