有时候在我们的网络应用中，防止程序自动登录搞破坏，我们一般都会加上验证码，这些验证码一般来说都是由人来识别的，当然，如果验证码很有规律，或者说很清楚，漂亮，那么也是可能被程序识别的，我以前就识别过某网站的验证码，因为比较有规律，所以被识别了，并且识别率达到99%左右，其实我们可以制作很复杂一点的验证码，添加一些干扰的线条或者字体变形，使程序识别的难度加大，这样，我们的目的也就达到了.

下面是生成的图片：

package com.hadeslee;

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.GradientPaint;
import java.awt.Graphics2D;
import java.awt.GraphicsEnvironment;
import java.awt.Paint;
import java.awt.Point;
import java.awt.Stroke;
import java.awt.image.BufferedImage;
import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.Random;
import javax.imageio.ImageIO;

import javax.servlet.*;
import javax.servlet.http.*;

/**
 *
 * @author lbf
 * @version
 */
public class Code extends HttpServlet {
    
    /** Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
     * @param request servlet request
     * @param response servlet response
     */
    private List<String> fonts=new ArrayList<String>();
    public Code(){
        initFonts();
    }
    private void initFonts(){
        GraphicsEnvironment.getLocalGraphicsEnvironment().preferLocaleFonts();
        String[] names=GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames(Locale.CHINA);
        for(String s:names){
            char c=s.charAt(0);
            if(Character.isLowerCase(c)||Character.isUpperCase(c)){
                
            }else{
                fonts.add(s);
            }
        }
    }
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("image/jpeg;charset=UTF-8");
        OutputStream out=response.getOutputStream();
        BufferedImage bi=new BufferedImage(200,50,BufferedImage.TYPE_INT_RGB);
        Graphics2D g=bi.createGraphics();
        char[] cs={'0','1','2','3','4','5','6','7','8','9'};
        char[] use=new char[4];
        g.setColor(new Color(240,240,240));
        g.fillRect(0,0,200,50);
        for(int i=0;i<4;i++){
            Point p=getPoint(i);
            int size=getSize();
            use[i]=cs[(int)(Math.random()*cs.length)];
           // g.setColor(new Color((int)(Math.random()*256),0,(int)(Math.random()*256)));
            g.setPaint(getPaint(p,size));
            g.setFont(new Font(fonts.get((int)(Math.random()*fonts.size())),getFace(),size));
            g.drawString(""+use[i],p.x,p.y);
        }
        g.setStroke(new BasicStroke(1.0f));
        g.setPaint(null);
        for(int i=0;i<4;i++){
            g.setColor(new Color((int)(Math.random()*0x00FFFFFFF)));
            g.drawLine((int)(Math.random()*200),(int)(Math.random()*50),(int)(Math.random()*200),(int)(Math.random()*50));
        }
        Random random = new Random();
        for (int i=0;i<88;i++) {
            int x = random.nextInt(200);
            int y = random.nextInt(50);
            g.setColor(new Color((int)(Math.random()*0x00FFFFFFF)));
            g.setStroke(getStroke());
            g.drawLine(x,y,x,y);
        }
        ImageIO.write(bi,"JPEG",out);
        out.close();
        g.dispose();
    }
    private Stroke getStroke(){
      BasicStroke bs=new BasicStroke((float)(Math.random()*3));
      return bs;
    }
    private Point getPoint(int index){
        return new Point(5+(index*((int)(Math.random()*10)+40)),40);
    }
    private Paint getPaint(Point p,int size){
        GradientPaint gp=new GradientPaint(p.x,p.y,new Color((int)(Math.random()*256),0,(int)(Math.random()*256)),
                p.x,p.y-size,new Color((int)(Math.random()*256),(int)(Math.random()*256),(int)(Math.random()*256)));
        return gp;
    }
    private int getFace(){
        if(Math.random()*10>5){
            return Font.BOLD;
        }else{
            return Font.ITALIC;
        }
    }
    private int getSize(){
        int[] sizes=new int[20];
        for(int i=0;i<20;i++){
            sizes[i]=30+i;
        }
        return sizes[(int)(Math.random()*sizes.length)];
    }
    
    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }
    
    /** Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }
    
    /** Returns a short description of the servlet.
     */
    public String getServletInfo() {
        return "Short description";
    }
    // </editor-fold>
}