01-随机字符验证码

页面 demo （jsp 生成）：

Java 代码 生成:

/**
 * 给定字符串随机获取4个字符，并使用StringBuilder拼接成字符串【验证码】
 */
public class GenerateCode {
	public static String identifyingCode() {
		String s = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
		StringBuilder sb = new StringBuilder();
		while (sb.length() < 4) {
			int index = (new java.util.Random()).nextInt(s.length());//0~s.length()-1
			// 处理重复字符：每个新的随机字符在 sb 中使用indexOf()查找下标值，-1为没找到，即不重复
			Character ch = new Character(s.charAt(index));
			if (sb.indexOf(ch.toString()) < 0) {
				sb.append(ch);
			}
		}
		return sb.toString();
	}
}

JSP 页面 生成:

// 刷新验证码
function refreshCode() {
    console.log("refreshCode");
    // 因浏览器的缓存技术，故需欺骗浏览器，每次点击是一次新的图片生成
    $("#validateCode").attr("src", "${pageContext.request.contextPath}/../validateCode.jsp?" + Math.random());
}

<!-- 验证码图片 -->
<!-- style="cursor:pointer" 验证码图片鼠标变手型 -->
验证码:<input type="text" name="validateCode">
<img
     src="${pageContext.request.contextPath}/validateCode.jsp"
     id="validateCode"
     style="cursor:pointer"
     onclick="refreshCode()"
>

validateCode.jsp - 生成验证码

<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8"%>
<%@ page import="java.util.Random"%>
<%@ page import="java.io.OutputStream"%>
<%@ page import="java.awt.Color"%>
<%@ page import="java.awt.Font"%>
<%@ page import="java.awt.Graphics"%>
<%@ page import="java.awt.image.BufferedImage"%>
<%@ page import="javax.imageio.ImageIO"%>
<%
    int width = 60;
    int height = 32;
    //创建图片对象
    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    Graphics g = image.getGraphics();
    //设置背景颜色
    g.setColor(new Color(0xDCDCDC));
    g.fillRect(0, 0, width, height);
    //设置边框
    g.setColor(Color.black);
    g.drawRect(0, 0, width - 1, height - 1);
    // create a random instance to generate the codes
    Random rdm = new Random();
    String hash1 = Integer.toHexString(rdm.nextInt());
    //画干扰线
    for (int i = 0; i < 50; i++) {
        int x = rdm.nextInt(width);
        int y = rdm.nextInt(height);
        g.drawOval(x, y, 0, 0);
    }
    //生成四位随机验证码
    String capstr = hash1.substring(0, 4);
    session.setAttribute("key", capstr);
    System.out.println(capstr);
    g.setColor(new Color(0, 100, 0));
    g.setFont(new Font("Candara", Font.BOLD, 24));
    g.drawString(capstr, 8, 24);
    g.dispose();
    response.setContentType("image/jpeg");
    out.clear();
    out = pageContext.pushBody();
    OutputStream strm = response.getOutputStream();
    ImageIO.write(image, "jpeg", strm);
    strm.close();
%>