小白教你用Java生成验证码

效果

• 点击验证码可切换
  

• 给出提示
  

一，生成验证码

package 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 cn.dsna.util.images.ValidateCode;

public class ShowVerifyCode extends HttpServlet {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	
	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		req.setCharacterEncoding("UTF-8");
		resp.setContentType("text/html;charset=utf-8");
		
		// 长100 宽100 4个字母 5 条干扰线的验证码
		ValidateCode validateCode = new ValidateCode(100, 50, 4, 4);
		ServletOutputStream out = resp.getOutputStream();
		
		String code = validateCode.getCode();
		
		// 验证码字符串保存到session对象
		req.getSession().setAttribute("code", code);
		
		// 把验证码图片写出去
		validateCode.write(out);
		
		out.close();
	}

}

二，页面收到验证码

	<script type="text/javascript">
	    // 刷新验证码！
		function refresh_code(obj) {
		// 多次请求
			obj.src = "showVerifyCode?id=" + new Date().getMilliseconds();
		}
		
		function check_verify_code(obj) {
			var ajax = new XMLHttpRequest();
			ajax.open("post", "checkVerifyCodeServlet?verifyCode=" + obj.value, true);
			
			ajax.onreadystatechange = function() {
				if (ajax.readyState == 4 && ajax.status == 200) {
					// response succeed...
					if (ajax.responseText == "false") {
						alert("验证码错误！");
						// disable submit commit...
					} else {
						// submit... do some code...
						
					}
				}
			};
			
			ajax.send(null);
			
		}
	</script>

• 图片src访问servlet，接收验证码图片

    <form action="">
    	name: <input type="text" name="name" /> <br/>
    	verifyCode:<input type="text" name="verifyCode" onblur="check_verify_code(this)"/> 
    	<img src="showVerifyCode" onclick="refresh_code(this)">
    </form>

三，验证验证码是否填写正确

	protected void service(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		Object code = req.getSession().getAttribute("code");
		String page_code = req.getParameter("verifyCode");
		
		System.out.println("生成的验证码 " + code + "\t页面验证码 " + page_code);
		
		PrintWriter out = resp.getWriter();
		
		if (code.toString().equalsIgnoreCase(page_code)) {
			// 页面验证码 = 后台的验证码！
			out.write("true");
		} else {
			out.write("false");
		}
		
		out.close();
	}