Java图片验证码的实现

       这里主要用到了三个文件，两个servlet类，一个JSP页面。两个servlet分别为drawCode.java和ValidateServlet.java，前者用来产生验证码，后者用来检验验证码是否正确，JSP页面为login.jsp，作为前台的交互。代码如下：

    login.jsp 

<%@ page language="java" pageEncoding="utf-8"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> 

	
		
		

		

			请您输入账号:
			
			


			请您输入密码:
			
			


			请输入验证码:
			
			
			
			


			
		
		
		
	 	
			
验证码错误
	     
	     
			
验证码正确
	     
	

    drawCode.java

package servlet;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.*;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class drawCode extends HttpServlet {

	public drawCode() {
		super();
	}

	public void destroy() {
		super.destroy(); 
	}
	
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doPost(request, response);
		
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
        
		  //设置页面不缓存    
	    response.setHeader("Pragma", "No-cache");    
	    response.setHeader("Cache-Control", "no-cache"); 
	    response.setDateHeader("Expires", 0);     
		// 在内存中创建图象 
		int width = 60, height = 20;
		BufferedImage image = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);
		//获取画笔
		Graphics g = image.getGraphics();
		//设定背景色 
		g.setColor(new Color(200, 200, 200));
		g.fillRect(0, 0, width, height);
		//取随机产生的验证码(4位数字) 
		Random rnd = new Random();
		int randNum = rnd.nextInt(8999) + 1000;
		String randStr = String.valueOf(randNum);
		//将验证码存入session
		request.getSession().setAttribute("randStr", randStr);
		//将验证码显示到图象中 
		g.setColor(Color.black);
		g.setFont(new Font("", Font.PLAIN, 20));
		g.drawString(randStr, 10, 17);
		// 随机产生100个干扰点，使图象中的验证码不易被其它程序探测到 
		for (int i = 0; i < 100; i++){
			int x = rnd.nextInt(width);
			int y = rnd.nextInt(height);
			g.drawOval(x, y, 1, 1);
		}  
      
		// 输出图象到页面 
		ImageIO.write(image, "JPEG", response.getOutputStream());
	}

	public void init() throws ServletException {
		// Put your code here
	}

}

ValidateServlet.java

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 {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		request.setCharacterEncoding("utf-8");		
		//判断验证码是否正确
		String code = request.getParameter("code");
		String randStr = request.getSession().getAttribute("randStr").toString();
		System.out.println(randStr);
		if(!code.equals(randStr)){
			response.sendRedirect("/Prj27/login.jsp?codeErro=yes");//验证码错误
			return ;
		}	
		else{
			response.sendRedirect("/Prj27/login.jsp?codeErro=no");//验证码正确
			return ;
		}
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doGet(request, response);		
	}
}

效果展示