接合网上和书上的实例，这是一个简单的实例。编码用的是UTF-8。各位在处理过程中一定要注意编码问题。
这个是code.jsp的源码：<%@ page language="java" import="java.awt.*" import="java.awt.image.BufferedImage" import="java.util.*" import="javax.imageio.ImageIO" pageEncoding="utf-8" %> <% response.setHeader("Cache-Control", "no-cache"); //create image in RAM! int width=60,height=20; BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); //get graphics Graphics g=image.getGraphics(); g.setColor(new Color(200,200,200)); g.fillRect(0, 0, width, height); //create randrom (4 namber) Random rnd = new Random(); int randNum=rnd.nextInt(8999)+1000; String randStr=String.valueOf(randNum); //save in session session.setAttribute("randStr", randStr); //display to image g.setColor(Color.black); g.setFont(new Font("",Font.PLAIN,20)); g.drawString(randStr, 10, 17); //100-other // //output image to page ImageIO.write(image, "JPEG", response.getOutputStream()); out.clear(); out=pageContext.popBody();%> 验证码的产生为1000+0-8999的随机值，使用1000+是确保第一位不为0，可以换成其它的汉字编码等其它不变。
它在网页中显示如下。
它在其它网页中调用如下：
该处理由servlet来处是，也可以由jsp等程序来处理。
下面说一下验证处理过程： 取得提交上来的验证码和session中的写入的验证码进行比较，相同则进行下一步处理，不同则报验证码错误。 下面是servlet处理的源代码：
package servlet;import java.io.IOException;import java.io.PrintWriter;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 ValidateServlet extends HttpServlet { /** * The doGet method of the servlet. * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //得到提交的验证码 String code=request.getParameter("code"); //获取session中的验证码 HttpSession session=request.getSession(); String randStr=(String)session.getAttribute("randStr"); response.setCharacterEncoding("utf-8"); PrintWriter out=response.getWriter(); if(!code.equals(randStr)){ out.println("验证码错误"); } else{ out.println("验证码正确!跳转到loginServlet.........."); } } /** * The doPost method of the servlet. * * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request, response); }}