蓝色记忆

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import com.sun.image.codec.jpeg.*;
import java.awt.*;
import com.sun.image.codec.jpeg.*;
import java.awt.image.BufferedImage;
import java.awt.image.DataBuffer;
import java.awt.geom.GeneralPath;
import javax.swing.*;
import java.math.*;
public class Servlet1
    extends HttpServlet {
//Process the HTTP Get request
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws
        ServletException, IOException {
    response.setContentType(request.getContentType());
    response.setContentType("image/jpeg"); //必须设置ContentType为image/jpeg
    int length = 4; //设置默认生成4个数字
    Date d = new Date();
    long lseed = d.getTime();
    java.util.Random r = new Random(lseed); //设置随机种子
    if (request.getParameter("length") != null) {
        try {
          length = Integer.parseInt(request.getParameter("length"));
        }
        catch (NumberFormatException e) {
        }
    }
    StringBuffer str = new StringBuffer();
    for (int i = 0; i < length; i++) {
        str.append(r.nextInt(9)); //生成随机数字
    }
//可以在此加入保存验证码的代码
//创建内存图像
    BufferedImage bi = new BufferedImage(40, 16, BufferedImage.TYPE_INT_RGB);
    Graphics2D g = bi.createGraphics();
    g.clearRect(0, 0, 16, 40);
    g.setColor(Color.RED);
    g.drawString(str.toString(), 4, 12);
    try {
//使用JPEG编码，输出到response的输出流
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.
            getOutputStream());
        JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(bi);
        param.setQuality(1.0f, false);
        encoder.setJPEGEncodeParam(param);
        encoder.encode(bi);
    }
    catch (Exception ex) {
    }
  }
} 然后在需求显示验证码的加入以下代码就可以了
<img alt="" src="/WebModule1/servlet1" width="40" height="16"/>