验证码配置方法

1.在web.xml下配置2个servlet，VerifyCodeServlet用来生成验证码图像，
ResultServlet用来做服务器端验证。

	<servlet>
		<servlet-name>VerifyCodeServlet</servlet-name>
		<servlet-class>VerifyCodeServlet</servlet-class>
	</servlet>
	<servlet>
		<servlet-name>ResultServlet</servlet-name>
		<servlet-class>ResultServlet</servlet-class>
	</servlet>
 	<servlet-mapping>
		<servlet-name>VerifyCodeServlet</servlet-name>
		<url-pattern>/verifyCodeServlet</url-pattern>
	</servlet-mapping>
	<servlet-mapping>
		<servlet-name>ResultServlet</servlet-name>
		<url-pattern>/resultServlet</url-pattern>
	</servlet-mapping>

2.servlet类文件

import java.awt.Color;   
import java.awt.Font;   
import java.awt.Graphics2D;   
import java.awt.image.BufferedImage;   
import java.util.Random;   
  
import javax.imageio.ImageIO;   
import javax.servlet.ServletException;   
import javax.servlet.ServletOutputStream;   
import javax.servlet.http.HttpServlet;   
import javax.servlet.http.HttpServletRequest;   
import javax.servlet.http.HttpServletResponse;   
import javax.servlet.http.HttpSession;   

public class VerifyCodeServlet extends HttpServlet {   
  
    
    /**
    * 验证码图片的宽度。 
    */
    private int width = 70;   
    
    /**
    *  验证码图片的高度。
    */
    private int height = 20;   
  
 
    /**
    * 验证码字符个数 
    */
    private int codeCount = 4;   
  
    /**
    * xx
    */
    private int xx = 0;   
  
    /**
    * 字体高度   
    */
    private int fontHeight;   
  
    /**
    * codeY
    */
    private int codeY;   
  
    /**
    * codeSequence
    */
    char[] codeSequence = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',   
            'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',   
            'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };   
  
    /**  
     * 初始化验证图片属性  
     */  
    public void init() throws ServletException {   
        // 从web.xml中获取初始信息   
        // 宽度   
        String strWidth = this.getInitParameter("width");   
        // 高度   
        String strHeight = this.getInitParameter("height");   
        // 字符个数   
        String strCodeCount = this.getInitParameter("codeCount");   
  
        // 将配置的信息转换成数值   
        try {   
            if (strWidth != null && strWidth.length() != 0) {   
                width = Integer.parseInt(strWidth);   
            }   
            if (strHeight != null && strHeight.length() != 0) {   
                height = Integer.parseInt(strHeight);   
            }   
            if (strCodeCount != null && strCodeCount.length() != 0) {   
                codeCount = Integer.parseInt(strCodeCount);   
            }   
        } catch (NumberFormatException e) {
         e.printStackTrace();
        }   
  
        xx = width / (codeCount + 1);   
        fontHeight = height - 2;   
        codeY = height - 4;   
  
    }   
  
    /**
    * @param req
    * @param resp
    * @throws ServletException
    * @throws java.io.IOException
    */
    protected void service(HttpServletRequest req, HttpServletResponse resp)   
            throws ServletException, java.io.IOException {   
  
        // 定义图像buffer   
        BufferedImage buffImg = new BufferedImage(width, height,   
                BufferedImage.TYPE_INT_RGB);   
        Graphics2D gd = buffImg.createGraphics();   
  
        // 创建一个随机数生成器类   
        Random random = new Random();   
  
        // 将图像填充为白色   
        gd.setColor(Color.WHITE);   
        gd.fillRect(0, 0, width, height);   
  
        // 创建字体，字体的大小应该根据图片的高度来定。   
        Font font = new Font("Fixedsys", Font.PLAIN, fontHeight);   
        // 设置字体。   
        gd.setFont(font);   
  
        // 画边框。   
        gd.setColor(Color.BLACK);   
        gd.drawRect(0, 0, width - 1, height - 1);   
  
        // 随机产生160条干扰线，使图象中的认证码不易被其它程序探测到。
        
        gd.setColor(Color.lightGray);   
        for (int i = 0; i < 16; i++) {   
            int x = random.nextInt(width);   
            int y = random.nextInt(height);   
            int xl = random.nextInt(12);   
            int yl = random.nextInt(12);   
            gd.drawLine(x, y, x + xl, y + yl);   
        }   
  
        // randomCode用于保存随机产生的验证码，以便用户登录后进行验证。   
        StringBuffer randomCode = new StringBuffer();   
        int red = 0, green = 0, blue = 0;   
  
        // 随机产生codeCount数字的验证码。   
        for (int i = 0; i < codeCount; i++) {   
            // 得到随机产生的验证码数字。   
            String strRand = String.valueOf(codeSequence[random.nextInt(36)]);   
            // 产生随机的颜色分量来构造颜色值，这样输出的每位数字的颜色值都将不同。   
            red = random.nextInt(255);   
            green = random.nextInt(255);   
            blue = random.nextInt(255);   
  
            // 用随机产生的颜色将验证码绘制到图像中。   
            gd.setColor(new Color(red, green, blue));   
            gd.drawString(strRand, (i + 1) * xx, codeY);   
  
            // 将产生的四个随机数组合在一起。   
            randomCode.append(strRand);   
        }   
        // 将四位数字的验证码保存到Session中。   
        HttpSession session = req.getSession();   
        session.setAttribute("validateCode", randomCode.toString());   
  
        // 禁止图像缓存。   
        resp.setHeader("Pragma", "no-cache");   
        resp.setHeader("Cache-Control", "no-cache");   
        resp.setDateHeader("Expires", 0);   
  
        resp.setContentType("image/jpeg");   
  
        // 将图像输出到Servlet输出流中。   
        ServletOutputStream sos = resp.getOutputStream();   
        ImageIO.write(buffImg, "jpeg", sos);   
        sos.close();   
    }   
  
} 

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;   
  
public class ResultServlet extends HttpServlet {   
  
    public void doGet(HttpServletRequest request, HttpServletResponse response)   
            throws ServletException, IOException {   
  
        doPost(request, response);   
    }   
  
    public void doPost(HttpServletRequest request, HttpServletResponse response)   
            throws ServletException, IOException {   
  
        response.setContentType("text/html;charset=utf-8");   
        String validateC = (String) request.getSession().getAttribute("validateCode");   
        String veryCode = request.getParameter("code");   
        PrintWriter out = response.getWriter();         
        veryCode = veryCode.toUpperCase();
        if(veryCode==null||"".equals(veryCode)){   
        	out.print("false");
        }else{   
            if(validateC.equals(veryCode)){   
            	out.print("true");
            }else{   
            	out.print("false");
            }   
        }   
        out.flush();   
        out.close();   
    }   
  
}  

3.jsp页面显示

<input type="text" id="checkCode" name="checkCode" class="s_td"/><img id="imgObj" alt="" src="<c:url value='/verifyCodeServlet'/>" style="vertical-align:top;margin-top:1px;margin-left:5px;"/>&nbsp;&nbsp;  
			        <a href="javascript:void(0);" onclick="changeImg();return false;">看不清,换一张</a> <span id="error"></span> 

4.ajax验证

		//------改变验证码内容------		
		function changeImg(){   
		    var imgSrc = $("#imgObj");   
		  	imgSrc.attr("src",chgUrl("<c:url value='/verifyCodeServlet'/>")); 
		  	$("#checkCode").focus();  
		}	
		//时间戳   
		//为了使每次生成图片不一致，即不让浏览器读缓存，所以需要加上时间戳   
		function chgUrl(url){   
		    var timestamp = (new Date()).valueOf();   
		    if((url.indexOf("&")>=0)){   
		        url = url + "&tamp=" + timestamp;   
		    }else{   
		        url = url + "?timestamp=" + timestamp;   
		    }   
		    return url;   
		}
		//判断输入的验证码是否正确
		function isRightCode(){   
		    var res = "false";
		    var code = $("#checkCode").attr("value");   
		    code = "data="+new Date()+"&code=" + code; 
		    $.ajax({
		        type:"POST",   
		        url:"<c:url value='/resultServlet'/>",   
		        data:code,   
		        //同步
		        async:false,
		        success:function(data){
		        res=data;
		        }
		    });
		    return res;
		}