效果图：
工具类CreateImageCode.java：
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;public class CreateImageCode { private int width = 70; private int height = 27; private int codeCount = 4; // 干扰线数 //private int lineCount = 10; // 验证码图片Buffer // 验证码 private String code = null; public String getCode() { return code; } public void setCode(String code) { this.code = code; } private BufferedImage buffImg = null; Random random = new Random(); public CreateImageCode() { createImage(); } public CreateImageCode(int width, int height) { this.width = width; this.height = height; createImage(); } public CreateImageCode(int width, int height, int codeCount) { this.width = width; this.height = height; this.codeCount = codeCount; createImage(); } public CreateImageCode(int width, int height, int codeCount, int lineCount) { this.width = width; this.height = height; this.codeCount = codeCount; //this.lineCount = lineCount; createImage(); } // 生成图片 private void createImage() { int fontWidth = width / codeCount;// 字体宽度。 int fontHeight = height - 5;// 字体高度。 int codeY = height - 8; // 得到图片 buffImg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); Graphics g = buffImg.getGraphics(); // 设置背景色 g.setColor(getRandColor(249, 250)); g.fillRect(0, 0, width, height); // 设置边框 //g.setColor(getRandColor(200, 250)); //g.drawRect(1, 1, width - 2, height - 2); // 设置字体 Font font = new Font("Fixedsys", Font.PLAIN, fontHeight); g.setFont(font); /*// 设置干扰线 for (int i = 0; i < lineCount; i++) { int x1 = random.nextInt(width); int y1 = random.nextInt(height); int x2 = random.nextInt(width); int y2 = random.nextInt(height); g.setColor(getRandColor(1, 255)); g.drawLine(x1, y1, x2, y2); }*/ /*// 添加噪点 float yawpRate = 0.01f;// 噪声率 int area = (int) (yawpRate * width * height); for (int i = 0; i < area; i++) { int x = random.nextInt(width); int y = random.nextInt(height); buffImg.setRGB(x, y, random.nextInt(255)); }*/ String str1 = randomStr(codeCount);// 得到随机字符 this.code = str1; for (int i = 0; i < codeCount; i++) { String strRand = str1.substring(i, i + 1); g.setColor(getRandColor(50, 250)); // g.drawString(a,x,y); // a为要画出来的东西，x和y表示要画的东西最左侧字符的基线位于此图形上下文坐标系的 (x, y) 位置处 g.drawString(strRand, i * fontWidth + 3, codeY); } } // 得到随机字符 private String randomStr(int n) { String str1 = "1234567890"; String str2 = ""; int len = str1.length() - 1; double r; for (int i = 0; i < n; i++) { r = (Math.random()) * len; str2 = str2 + str1.charAt((int) r); } return str2; } // 得到随机颜色 private Color getRandColor(int fc, int bc) { // 给定范围获得随机颜色 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); } public void write(OutputStream sos) throws IOException { ImageIO.write(buffImg, "png", sos); sos.close(); }} 在servlet中使用此工具类，输出验证码到网页：
package com.utils;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet(name = "GetImageCodeServlet",urlPatterns = {"/servlet/code.servlet"})public class GetImageCodeServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("image/jepg"); // 控制浏览器不要缓存 response.setDateHeader("expries", -1); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Pragma", "no-cache"); // 创建图片 CreateImageCode image = new CreateImageCode(); String str = image.getCode(); // 存入Session// System.out.println("验证码为"+str); request.getSession().setAttribute("code",str); // 输出到网页 image.write(response.getOutputStream()); }} JSP中在表单显示此图片（演示时不使用Ajax，直接将form提交到另一个servlet判断）：
后台验证验证码的servlet：
package com.utils;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet(name = "CodeTestServlet" ,urlPatterns = {"/servlet/codeTest.servlet"})public class CodeTestServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String code = request.getParameter("code"); if (code.equals(request.getSession().getAttribute("code"))) { System.out.println("验证成功，验证码为：" + request.getSession().getAttribute("code")); // response.sendRedirect(getServletContext().getContextPath()+"/login.jsp"); }else{ System.out.println("验证失败"); } }} ----
使用的是3.0的注解开发，web.xml中不需配置
若为maven项目，依赖为：
javax.servlet javax.servlet-api 3.1.0 javax.servlet.jsp javax.servlet.jsp-api 2.3.1