Java 使用jsp和servlet实现验证码功能

验证码主要是为了防止我们的网站被有些人和黑客恶意攻击，比如我们网站的注册页面，如果我们在用户注册的时候不加上一个验证码框的话，别人就可以写一个脚本对你的网站进行恶意的注册，比如每分钟对你的网站进行n次的注册，那么你的网站就会被攻击而崩溃。当我们增加了验证码之后，别人再写脚本的时候就必须先识别你的验证码，而要识别图片验证码中的内容，却不是那么的容易，但是客户往往不知道我们加验证码是用来干什么的，认为会很麻烦，但是我们开发过程中是一定要加的，因为我们的验证码目前图片形式的，而且歪歪斜斜乱七八糟，而现阶段图形模式识别技术还没做到能够识别验证码的程度，所以加上验证码就相对安全了很多，直接上代码：

jsp前段代码：

<img src="/validateCodeServlet" onclick="Refresh(this);" class="mid ${name}" style="${imageCssStyle}"/>

<script type="text/javascript">

//刷新验证码
Refresh= function(obj) {
obj.src ='/validateCodeServlet?'+new Date();
}

</script>

web.xml中配置一定加上：

<servlet>
<servlet-name>ValidateCodeServlet</servlet-name>
<servlet-class>cn.common.modules.utils.ValidateCodeServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ValidateCodeServlet</servlet-name>
<url-pattern>/utils/validateCodeServlet</url-pattern>
</servlet-mapping>

接下来就是我们的ValidateCodeServlet后台代码了；

package cn.common.modules.utils;

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

import org.apache.commons.lang3.math.NumberUtils;
import org.apache.commons.lang3.StringUtils;

/**
* 生成随机验证码
*/
@SuppressWarnings("serial")
public class ValidateCodeServlet1 extends HttpServlet {

public static final String VALIDATE_CODE = "validateCode";

private int w = 70;
private int h = 26;

public ValidateCodeServlet1() {
super();
}

public void destroy() {
super.destroy();
}

public static boolean validate(HttpServletRequest request, String validateCode){
String code = (String)request.getSession().getAttribute(VALIDATE_CODE);
return validateCode.toUpperCase().equals(code);
}

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String validateCode = request.getParameter(VALIDATE_CODE); // AJAX验证，成功返回true
if (StringUtils.isNotBlank(validateCode)){
response.getOutputStream().print(validate(request, validateCode)?"true":"false");
}else{
this.doPost(request, response);
}
}

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

private void createImage(HttpServletRequest request,
HttpServletResponse response) throws IOException {

response.setHeader("Pragma", "no-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
response.setContentType("image/jpeg");

/*
* 得到参数高，宽，都为数字时，则使用设置高宽，否则使用默认值
*/
String width = request.getParameter("width");
String height = request.getParameter("height");
if (StringUtils.isNumeric(width) && StringUtils.isNumeric(height)) {
w = NumberUtils.toInt(width);
h = NumberUtils.toInt(height);
}

BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();

/*
* 生成背景
*/
createBackground(g);

/*
* 生成字符
*/
String s = createCharacter(g);
request.getSession().setAttribute(VALIDATE_CODE, s);

g.dispose();
OutputStream out = response.getOutputStream();
ImageIO.write(image, "JPEG", out);
out.close();

}

private Color getRandColor(int fc,int bc) {
int f = fc;
int b = bc;
Random random=new Random();
if(f>255) {
f=255;
}
if(b>255) {
b=255;
}
return new Color(f+random.nextInt(b-f),f+random.nextInt(b-f),f+random.nextInt(b-f));
}

private void createBackground(Graphics g) {
// 填充背景
g.setColor(getRandColor(220,250));
g.fillRect(0, 0, w, h);
// 加入干扰线条
for (int i = 0; i < 8; i++) {
g.setColor(getRandColor(40,150));
Random random = new Random();
int x = random.nextInt(w);
int y = random.nextInt(h);
int x1 = random.nextInt(w);
int y1 = random.nextInt(h);
g.drawLine(x, y, x1, y1);
}
}

private String createCharacter(Graphics g) {
char[] codeSeq = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J',
'K', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
'X', 'Y', 'Z', '2', '3', '4', '5', '6', '7', '8', '9' };
String[] fontTypes = {"Arial","Arial Black","AvantGarde Bk BT","Calibri"};
Random random = new Random();
StringBuilder s = new StringBuilder();
for (int i = 0; i < 4; i++) {
String r = String.valueOf(codeSeq[random.nextInt(codeSeq.length)]);//random.nextInt(10));
g.setColor(new Color(50 + random.nextInt(100), 50 + random.nextInt(100), 50 + random.nextInt(100)));
g.setFont(new Font(fontTypes[random.nextInt(fontTypes.length)],Font.BOLD,26));
g.drawString(r, 15 * i + 5, 19 + random.nextInt(8));
// g.drawString(r, i*w/4, h-5);
s.append(r);
}
return s.toString();
}
}

最后就可以生成一个含有字母和数字的一个图片了