servlet实现一次性验证码

最新推荐文章于 2021-09-02 07:22:39 发布

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最新推荐文章于 2021-09-02 07:22:39 发布

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分类专栏： java web 文章标签：验证码 servlet验证码一次性验证码 java验证码图形码

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本文介绍了使用Java生成验证码的基本思路及其实现过程，包括如何将生成的验证码保存到session中，以及在表单提交时如何与客户端提交的验证码进行比较。此外，还讨论了在用户禁用cookie情况下如何实现验证码验证，以及可以进一步拓展的验证码形式。

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大致的思路：先用java生成验证码，然后将生成的验证码保存到session中，在表单提交时，将保存到session中的验证码与表单提交的验证码进行比较，然后输出不同的结果。其实还可以实现一个目标，在用户禁用cookie也能验证成功，那就需要url重写了。这个例子只是给了一个简单的验证码的实现，当然可以根据实际的需求写出更加精彩的验证码，比如“汉字”验证码，算术验证码。本文只是给怎样实现验证码提供了一个基本的思路。

ImageCodeUtil.java

package cn.zq.util;

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

import javax.imageio.ImageIO;

/**
 * 图形码工具类
 * @author zq
 */
public class ImageCodeUtil {
	
	/**
	 * 下面配置的这些常量，最好的办法就是通过配置文件来获取，下面直接写死了
	 */
	
	/**
	 * 图形码的宽
	 */
	private static final int IMAGE_CODE_WIDTH = 120;
	
	/**
	 * 图形码的高
	 */
	private static final int IMAGE_CODE_HEIGHT = 60;
	
	/**
	 * 图形码个数
	 */
	private static final int IMAGE_CODE_NUM = 4;
	
	/**
	 * 图形码最多干扰线数量
	 */
	private static final int IMAGE_CODE_MAX_LINE_NUM = 15;
	
	/**
	 * 图形码最小干扰线数量
	 */
	private static final int IMAGE_CODE_MIN_LINE_NUM = 10;
	
	/**
	 * 图片类型
	 */
	private static final String IMAGE_TYPE = "jpg";
	
	/**
	 * 图形码取数
	 */
	private static final String IMAGE_CODE_DATA = "ABCDEFGHIJKLMNOPQRSJUVWXYZabcdefghijklmnopqrsjuvwxyz0123456789";
	
	private static final Random rand = new Random();
	
	
	/**
	 * 生成图形码
	 * @param os OutputStream 接受 流
	 * @return String 图形码
	 */
	public static String generateSimpleImageCode(OutputStream os){
		return generateSimpleImageCode(os, true);
	}
	
	/**
	 * 生成图形码
	 * @param os OutputStream 接受 流
	 * @param drawLine boolean 是否画干扰线
	 * @return String 图形码
	 */
	public static String generateSimpleImageCode(OutputStream os, boolean drawLine){
		StringBuilder code = new StringBuilder();
		try {
			//创建一张图片
			BufferedImage image = new BufferedImage(IMAGE_CODE_WIDTH, IMAGE_CODE_HEIGHT, BufferedImage.TYPE_INT_RGB);
			
			//拿到画笔
			Graphics g = image.getGraphics();
			
			//画边框
			g.drawRect(0, 0, IMAGE_CODE_WIDTH, IMAGE_CODE_HEIGHT);
			g.setColor(Color.WHITE);
			g.fillRect(0, 0, IMAGE_CODE_WIDTH, IMAGE_CODE_HEIGHT);
			
			//产生随机码
			for(int i = 0; i < IMAGE_CODE_NUM; i++){
				int index = rand.nextInt(IMAGE_CODE_DATA.length());
				String str = String.valueOf(IMAGE_CODE_DATA.charAt(index));
				code.append(str);
				
				g.setFont(new Font("宋体", Font.PLAIN, 30));
				g.setColor(new Color(rand.nextInt(255), rand.nextInt(255), rand.nextInt(255)));
				g.drawString(str, 10 + 30 * i, 40 + rand.nextInt(6));
			}
			
			if (drawLine) {
				int randLineNum = IMAGE_CODE_MIN_LINE_NUM + 
						rand.nextInt(IMAGE_CODE_MAX_LINE_NUM - IMAGE_CODE_MIN_LINE_NUM);
				//画干扰线
				for(int i = 0; i < randLineNum; i++){
					g.setColor(new Color(rand.nextInt(255), rand.nextInt(255), rand.nextInt(255)));
					g.drawLine(rand.nextInt(IMAGE_CODE_WIDTH), 
							rand.nextInt(IMAGE_CODE_HEIGHT), 
							rand.nextInt(IMAGE_CODE_WIDTH), 
							rand.nextInt(IMAGE_CODE_HEIGHT));
				}
			}
			ImageIO.write(image, IMAGE_TYPE, os);
			return code.toString();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
	
	public static void main(String[] args) throws Exception{
		System.out.println(IMAGE_CODE_DATA.length());
		FileOutputStream fos = new FileOutputStream("c:\\imagecode.jpg");
		String code  = generateSimpleImageCode(fos);
		fos.close();
		System.out.println(code);
	}
}

GetImageCodeServlet.java

package cn.zq.servlet;

import java.io.IOException;

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;

import cn.zq.util.ImageCodeUtil;

public class GetImageCodeServlet extends HttpServlet {

	private static final long serialVersionUID = 5225185955711424724L;

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

		doPost(request, response);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//设置浏览器不要缓存
		response.setHeader("pragma", "no-cache");
		response.setHeader("cache-control", "no-cache");
		response.setHeader("expires", "0");
		response.setContentType("image/jpeg");
		HttpSession session = request.getSession();
		ServletOutputStream sos = response.getOutputStream();
		String code = ImageCodeUtil.generateSimpleImageCode(sos);
		session.setAttribute("imageCode", code);
	}

}

FormServlet.java

package cn.zq.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 FormServlet extends HttpServlet {

	private static final long serialVersionUID = -5699696644228229140L;

	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");
		
		//获取客户端提交的图像码
		String clientImageCode = request.getParameter("imageCode");
		
		HttpSession session = request.getSession();

		//获取服务器端的图像码
		String serverImageCode = (String) session.getAttribute("imageCode");
		
		
		PrintWriter out = response.getWriter();
		
		if(serverImageCode != null){
			
			if(serverImageCode.equalsIgnoreCase(clientImageCode)){
				out.print("已经通过验证！");
			}else{
				out.print("验证码输入有误");
			}
			
			session.removeAttribute("imageCode");
		}else{
			out.print("验证码失效！");
		}
	}

}

form.html

<span style="color:#000000;"><!DOCTYPE html>
<html>
  <head>
    <title>输入验证码</title>
  </head>
  
  <body>
    <form  action="formServlet" method="post">
     	<input type="text" name="imageCode"><img  src="getImageCodeServlet" border="1px"> <br/>
     	<input type="submit" value="验证">
    </form>
  </body>
</html></span>

web.xml文件的有关配置:

<span style="color:#000000;"><?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <servlet>
    <servlet-name>GetImageCodeServlet</servlet-name>
    <servlet-class>cn.zq.servlet.GetImageCodeServlet</servlet-class>
  </servlet>
  <servlet>
    <servlet-name>FormServlet</servlet-name>
    <servlet-class>cn.zq.servlet.FormServlet</servlet-class>
  </servlet>


  <servlet-mapping>
    <servlet-name>GetImageCodeServlet</servlet-name>
    <url-pattern>/getImageCodeServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>FormServlet</servlet-name>
    <url-pattern>/formServlet</url-pattern>
  </servlet-mapping>
</web-app></span>

验证码效果如下图：

与验证码类似的经典问题有，怎样防止表单重复提交，这类问题很有意思，防止表单提交的要点就是在表单用隐藏域保存从服务器端获取的值，当表单提交时，拿这个值与服务器端的值进行比较。大致的思路与验证码很类型，都是在服务器端存放值，在从客户浏览器表单提交时获取客户端的值进行比较。源代码可以再这里下载 http://download.youkuaiyun.com/detail/qq791967024/8408511