验证码的实现

     验证码的实现方式主要有两种，一种是手动模拟的形式，其基本的思想是将进行画图操作，并将其输出为图片格式，如jpeg等。而另外一种则是借助Validate工具包（jar包），由它来实现验证码的显示，只需要设置对应的参数（推荐）。

    1、手动模拟

package com.ms.servlet;

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;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CheckcodeServlet2 extends HttpServlet {
	private int width;
	private int height;
	private int number; //显示多少个字符串
	private String codes;	
	
	
	//初始化
	@Override
	public void init(ServletConfig config) throws ServletException {
		width = Integer.parseInt(config.getInitParameter("width"));
		height = Integer.parseInt(config.getInitParameter("height"));
		number =Integer.parseInt( config.getInitParameter("number"));
		codes = config.getInitParameter("codes");
	}

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		
		//画图
		BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
		Graphics g = image.createGraphics();
		
		//创建白色背景
		g.setColor(Color.white);
		g.fillRect(0, 0, width, height);
		
		//画黑边圈
		g.setColor(Color.black);
		g.drawRect(0, 0, width-1, height-1);
		
		Random random = new Random();
		
		//每个字符占据的宽度
		int x = (width - 1) / number;
		int y = height -4;
		
		//随机生成字符
		for(int i=0; i<number; i++){
			String code = String.valueOf( codes.charAt( random.nextInt(codes.length())) );
			int red = random.nextInt(255);
			int green = random.nextInt(255);
			int blue = random.nextInt(255);
			g.setColor(new Color(red,green,blue));
			
			Font font = new Font("Arial",Font.PLAIN,random(height/2,height));
			g.setFont(font);
			
			g.drawString(code, i * x + 1, y);
		}
		
		//随机生成一些点
		for(int i=0; i<50; i++){
			int red = random.nextInt(255);
			int green = random.nextInt(255);
			int blue = random.nextInt(255);
			g.setColor(new Color(red,green,blue));
			g.drawOval(random.nextInt(width), random.nextInt(height), 1, 1);
		}

		
		OutputStream out = response.getOutputStream();
		//将图片转换为JPEG类型
		response.setContentType("image/jpeg");
		ImageIO.write(image, "image/jpeg", out);
		out.flush();

	}
	
	/**
	 * 产生一个从min到max之间的随机数
	 * @param min
	 * @param max
	 * @return
	 */
	private int random(int min,int max){
		int m = new Random().nextInt(999999) % (max - min);
		return m + min;
	}



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

    2、Validate的使用

package com.ms.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import cn.dsna.util.images.ValidateCode;

public class test01 extends HttpServlet {
	
	private int width;
	private int height;
	private int number; //显示多少个字符串
	private String codes;	
	
	
	//初始化
	@Override
	public void init(ServletConfig config) throws ServletException {
		width = Integer.parseInt(config.getInitParameter("width"));
		height = Integer.parseInt(config.getInitParameter("height"));
		number =Integer.parseInt( config.getInitParameter("number"));
	}
	
	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
                /*第一个参数为宽，第二个参数为高，第三个参数为验证码内容的个数，第四个参数为线条的数量*/
		ValidateCode vc = new ValidateCode(width,height,number,5);
		request.getSession().setAttribute("scode", vc.getCode());
		vc.write(response.getOutputStream());
	}

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

}

    3、两者之间web.xml的配置（这里提供基于jar包实现的配置，关于手动方式的配置是一样的）

<servlet>
    <servlet-name>test</servlet-name>
    <servlet-class>com.ms.servlet.test01</servlet-class>
      	<init-param>
  		<param-name>width</param-name>
  		<param-value>50</param-value>
  	</init-param>
  	 	<init-param>
  		<param-name>height</param-name>
  		<param-value>20</param-value>
  	</init-param>
  	 	<init-param>
  		<param-name>number</param-name>
  		<param-value>4</param-value>
  	</init-param>
  </servlet>


  <servlet-mapping>
    <servlet-name>test</servlet-name>
    <url-pattern>/backend/images/checkcode.jpg</url-pattern>
  </servlet-mapping>
  

    4、jsp端的代码

<!-- safecode.setAttribute('src','images/checkcode.jpg?'+Math.random()); -->
<script type="text/javascript">
        function changecode(){
		var safecode = document.getElementById("safecode");
		safecode.src="images/checkcode.jpg?"+Math.random(); //在线进行验证码的点击更新
	}
</script>

 <img src="images/checkcode.jpg" id="safecode" onclick="changecode()"/>