java中登录验证码的使用

jsp、html、vm、ftl界面
<tr>
	<td><span style="display:block;text-align:right;">验证码：</span></td>
	<td><input type="text" class="form-control" style="width:130px;" id="validate-code" ></td>
	<td> <img id="gen-validate-img" alt="验证码" src="${request.contextPath}/dsna.images" title="看不清楚，点击获得新图片"/></td>
</tr>

web.xml中配置
<servlet>
	<servlet-name>validateCodeServlet</servlet-name>
	<servlet-class>com.ctfo.zjz.util.images.ValidateCodeServlet</servlet-class><!--这里需要修改为自己的路径，调用ValidateCodeServlet类-->
</servlet>	
<servlet-mapping>
	<servlet-name>validateCodeServlet</servlet-name>
	<url-pattern>*.images</url-pattern><!--这里对应页面中的的验证码图片地址-->
</servlet-mapping>

ValidateCodeServlet类（直接用，不需要修改）
package com.ctfo.zjz.util.images;
import java.io.IOException;
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 ValidateCodeServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	@Override
	protected void doGet(HttpServletRequest reqeust,
			HttpServletResponse response) throws ServletException, IOException {
		// 设置响应的类型格式为图片格式
		response.setContentType("image/jpeg");
		//禁止图像缓存。
		response.setHeader("Pragma", "no-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		
		HttpSession session = reqeust.getSession();//获取session对象
		
		ValidateCode vCode = new ValidateCode(120,35,4,10);//生成验证码图片
		session.setAttribute("code", vCode.getCode());//向session中保存验证码
		vCode.write(response.getOutputStream());//输出验证码图片
	}
}
ValidateCode类（验证码生成器，直接用不需要修改）

package com.ctfo.zjz.util.images;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;

import javax.imageio.ImageIO;
/**
 * 验证码生成器
 * @author dsna
 *
 */
public class ValidateCode {
	// 图片的宽度。
	private int width = 160;
	// 图片的高度。
	private int height = 40;
	// 验证码字符个数
	private int codeCount = 5;
	// 验证码干扰线数
	private int lineCount = 150;
	// 验证码
	private String code = null;
	// 验证码图片Buffer
	private BufferedImage buffImg=null;

	private char[] codeSequence = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H','J',
			'K', 'L', 'M', 'N',  'P', 'Q', 'R', 'S', 'T', 'U', 'V', 
			'X', 'Y', 'Z',  '1', '2', '3', '4', '5', '6', '7', '8', '9' };

	public  ValidateCode() {
		this.createCode();
	}

	/**
	 * 
	 * @param width 图片宽
	 * @param height 图片高
	 */
	public  ValidateCode(int width,int height) {
		this.width=width;
		this.height=height;
		this.createCode();
	}
	/**
	 * 
	 * @param width 图片宽
	 * @param height 图片高
	 * @param codeCount 字符个数
	 * @param lineCount 干扰线条数
	 */
	public  ValidateCode(int width,int height,int codeCount,int lineCount) {
		this.width=width;
		this.height=height;
		this.codeCount=codeCount;
		this.lineCount=lineCount;
		this.createCode();
	}
	
	public void createCode() {
		int x = 0,fontHeight=0,codeY=0;
		int red = 0, green = 0, blue = 0;
		
		x = width / (codeCount);//每个字符的宽度
		fontHeight = height - 2;//字体的高度
		codeY = height - 4; //验证码高度
		
		// 图像buffer
		buffImg = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);
		Graphics2D g = buffImg.createGraphics();
		// 生成随机数
		Random random = new Random();
		// 将图像填充为白色
		g.setColor(Color.WHITE);
		g.fillRect(0, 0, width, height);
		// 创建字体
		ImgFontByte imgFont=new ImgFontByte();
		Font font =imgFont.getFont(fontHeight);
		g.setFont(font);
		
		for (int i = 0; i < lineCount; i++) {
			int xs = random.nextInt(width);
			int ys = random.nextInt(height);
			int xe = xs+random.nextInt(width/8);
			int ye = ys+random.nextInt(height/8);
			red = random.nextInt(255);
			green = random.nextInt(255);
			blue = random.nextInt(255);
			//g.setColor(new Color(red, green, blue));
			g.setColor(new Color(0, 0, 0));
			g.drawLine(xs, ys, xe, ye);
		}		
		// randomCode记录随机产生的验证码
		StringBuffer randomCode = new StringBuffer();
		// 随机产生codeCount个字符的验证码。
		for (int i = 0; i < codeCount; i++) {
			String strRand = String.valueOf(codeSequence[random.nextInt(codeSequence.length)]);
			// 产生随机的颜色值，让输出的每个字符的颜色值都将不同。
			red = random.nextInt(255);
			green = random.nextInt(255);
			blue = random.nextInt(255);
			//g.setColor(new Color(red, green, blue));
			g.setColor(new Color(255, 0, 0));
			//图片生成的位置
			//第二个参数：表示验证码在图片中出现的x轴的位置，值越小越靠左
			//第三个参数：表示验证码在图片中出现的y轴的位置，值越大越靠上
			g.drawString(strRand, i* x + 5, 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。
		code=randomCode.toString();
	}
	
	public void write(String path) throws IOException {
		OutputStream sos = new FileOutputStream(path);
			this.write(sos);
	}
	
	public void write(OutputStream sos) throws IOException {
			ImageIO.write(buffImg, "png", sos);
			sos.close();
	}
	public BufferedImage getBuffImg() {
		return buffImg;
	}
	
	public String getCode() {
		return code;
	}
}
ImgFontByte.java(字体工具类，直接用，不需要修改)
package com.ctfo.zjz.util.images;
import java.io.ByteArrayInputStream;
import java.awt.*;
/**
 * ttf字体文件
 * @author dsna
 *
 */
public class ImgFontByte {
	public Font getFont(int fontHeight){
		try {
			Font baseFont = Font.createFont(Font.TRUETYPE_FONT, new ByteArrayInputStream(hex2byte(getFontByteStr())));
			return baseFont.deriveFont(Font.PLAIN, fontHeight);
		} catch (Exception e) {
			return new Font("Arial",Font.PLAIN, fontHeight);
		}
	}
	
	private  byte[] hex2byte(String str) { 
		if (str == null)
			return null;
		str = str.trim();
		int len = str.length();
		if (len == 0 || len % 2 == 1)
			return null;

		byte[] b = new byte[len / 2];
		try {
			for (int i = 0; i < str.length(); i += 2) {
				b[i / 2] = (byte) Integer
						.decode("0x" + str.substring(i, i + 2)).intValue();
			}
			return b;
		} catch (Exception e) {
			return null;
		}
	}
	/**
	  * ttf字体文件的十六进制字符串
      * @return
      */
	private String getFontByteStr(){ 
		return null;
		//return str;//字符串太长 在附件中找
	}
}

在java中直接这样用
	/**
	 * @Description: 验证码校验
	 * @param code
	 * @param session
	 * @return
	 */
	@RequestMapping("/validate")
	@ResponseBody
	public String validate(String code, HttpSession session) {
		// 默认成功
		String flag = "0";
		if (StrUtil.isNotBlank(code)) {
			if (code.equalsIgnoreCase(session.getAttribute("code").toString())) {
				flag = "0";
			} else {
				flag = "1";
			}
		} else {
			flag = "1";
		}
		return flag;
	}