Use java to implement a verification code function

Verification codes can be seen everywhere in our daily lives. It can protect the security of our accounts to a certain extent, so how to achieve it?

(Learning video recommendation:java course)

The implementation of the verification code verification function in Java is actually very simple: a Graphics class is used to draw letters on the drawing board, and a certain number is randomly selected. A number of letters are randomly generated, and then several interference lines are randomly generated on the drawing board.

First, write a verification code generation helper class to draw random letters:

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; public final class GraphicHelper { /** * 以字符串形式返回生成的验证码，同时输出一个图片 * * @param width * 图片的宽度 * @param height * 图片的高度 * @param imgType * 图片的类型 * @param output * 图片的输出流(图片将输出到这个流中) * @return 返回所生成的验证码(字符串) */ public static String create(final int width, final int height, final String imgType, OutputStream output) { StringBuffer sb = new StringBuffer(); Random random = new Random(); BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); Graphics graphic = image.getGraphics(); graphic.setColor(Color.getColor("F8F8F8")); graphic.fillRect(0, 0, width, height); Color[] colors = new Color[] { Color.BLUE, Color.GRAY, Color.GREEN, Color.RED, Color.BLACK, Color.ORANGE, Color.CYAN }; // 在 "画板"上生成干扰线条 ( 50 是线条个数) for (int i = 0; i < 50; i++) { graphic.setColor(colors[random.nextInt(colors.length)]); final int x = random.nextInt(width); final int y = random.nextInt(height); final int w = random.nextInt(20); final int h = random.nextInt(20); final int signA = random.nextBoolean() ? 1 : -1; final int signB = random.nextBoolean() ? 1 : -1; graphic.drawLine(x, y, x + w * signA, y + h * signB); } // 在 "画板"上绘制字母 graphic.setFont(new Font("Comic Sans MS", Font.BOLD, 30)); for (int i = 0; i < 6; i++) { final int temp = random.nextInt(26) + 97; String s = String.valueOf((char) temp); sb.append(s); graphic.setColor(colors[random.nextInt(colors.length)]); graphic.drawString(s, i * (width / 6), height - (height / 3)); } graphic.dispose(); try { ImageIO.write(image, imgType, output); } catch (IOException e) { e.printStackTrace(); } return sb.toString(); } }

Then, create a servlet to fix the image size and handle the usage scenarios of the verification code, and Capture the verification code generated by the page (the captured QR code must be consistent with the verification code entered by the user to pass).

import java.io.IOException; import java.io.OutputStream; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; @WebServlet(urlPatterns = "/verify/regist.do" ) public class VerifyCodeServlet extends HttpServlet { private static final long serialVersionUID = 3398560501558431737L; @Override protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 获得 当前请求 对应的 会话对象 HttpSession session = request.getSession(); // 从请求中获得 URI ( 统一资源标识符 ) String uri = request.getRequestURI(); System.out.println("hello : " + uri); final int width = 180; // 图片宽度 final int height = 40; // 图片高度 final String imgType = "jpeg"; // 指定图片格式 (不是指MIME类型) final OutputStream output = response.getOutputStream(); // 获得可以向客户端返回图片的输出流 // (字节流) // 创建验证码图片并返回图片上的字符串 String code = GraphicHelper.create(width, height, imgType, output); System.out.println("验证码内容: " + code); // 建立 uri 和 相应的 验证码 的关联 ( 存储到当前会话对象的属性中 ) session.setAttribute(uri, code); System.out.println(session.getAttribute(uri)); } }

(recommended related tutorials:Getting Started with Java)

Then write an HTML registration page to check it out:

Rendering:

The changes in the verification code in the picture received by the console are as follows:

When you click to refresh the page, the verification The code will also change, but when we can't see the verification code clearly, just click on the verification code and it will be refreshed. In this way, partial refresh can be achieved with JavaScript.

In, add a question mark and a string of suffix numbers. When refreshing, let the suffix numbers continue to change, then the formed verification code will also will continue to change. One method we can use is to replace the suffix number with date. Date gets the local time. The time changes at any time. This ensures that the refresh verification code can change at any time.

The code is as follows:

function myRefersh( e ) { const source = e.src ; // 获得原来的 src 中的内容 //console.log( "source : " + source ) ; var index = source.indexOf( "?" ) ; // 从 source 中寻找 ? 第一次出现的位置 (如果不存在则返回 -1 ) //console.log( "index : " + index ) ; if( index > -1 ) { // 如果找到了 ? 就进入内部 var s = source.substring( 0 , index ) ; // 从 source 中截取 index 之前的内容 ( index 以及 index 之后的内容都被舍弃 ) //console.log( "s : " + s ) ; var date = new Date(); // 创建一个 Date 对象的 一个 实例 var time = date.getTime() ; // 从 新创建的 Date 对象的实例中获得该时间对应毫秒值 e.src = s + "?time=" + time ; // 将 加了 尾巴 的 地址 重新放入到 src 上 //console.log( e.src ) ; } else { var date = new Date(); e.src = source + "?time=" + date.getTime(); } }

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