要實現(xiàn)頁面驗證碼的校驗，首先我們要先生成驗證碼
我們需要先準備一些東西
1）驗證碼生成的java類文件以及字段.txt文件炊苫，網(wǎng)絡上有各種資源可以獲取
下面是其一代碼文件：

package com.request.checkimg;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
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;

/**
 * 驗證碼生成程序
 * 
 * 
 * 
 */
public class CheckImgServlet extends HttpServlet {

    // 集合中保存所有成語
    private List<String> words = new ArrayList<String>();

    @Override
    public void init() throws ServletException {
        // 初始化階段，讀取new_words.txt
        // web工程中讀取 文件，必須使用絕對磁盤路徑
        String path = getServletContext().getRealPath("/WEB-INF/new_words.txt");
        try {
            BufferedReader reader = new BufferedReader(new FileReader(path));
            String line;
            while ((line = reader.readLine()) != null) {
                words.add(line);
            }
            reader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 禁止緩存
        // response.setHeader("Cache-Control", "no-cache");
        // response.setHeader("Pragma", "no-cache");
        // response.setDateHeader("Expires", -1);

        int width = 120;
        int height = 30;

        // 步驟一 繪制一張內(nèi)存中圖片
        BufferedImage bufferedImage = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_RGB);

        // 步驟二 圖片繪制背景顏色 ---通過繪圖對象
        Graphics graphics = bufferedImage.getGraphics();// 得到畫圖對象 --- 畫筆
        // 繪制任何圖形之前 都必須指定一個顏色
        graphics.setColor(getRandColor(200, 250));
        graphics.fillRect(0, 0, width, height);

        // 步驟三 繪制邊框
        graphics.setColor(Color.WHITE);
        graphics.drawRect(0, 0, width - 1, height - 1);

        // 步驟四 四個隨機數(shù)字
        Graphics2D graphics2d = (Graphics2D) graphics;
        // 設置輸出字體
        graphics2d.setFont(new Font("宋體", Font.BOLD, 18));

        Random random = new Random();// 生成隨機數(shù)
        int index = random.nextInt(words.size());
        String word = words.get(index);// 獲得成語

        // 定義x坐標
        int x = 10;
        for (int i = 0; i < word.length(); i++) {
            // 隨機顏色
            graphics2d.setColor(new Color(20 + random.nextInt(110), 20 + random
                    .nextInt(110), 20 + random.nextInt(110)));
            // 旋轉(zhuǎn) -30 --- 30度
            int jiaodu = random.nextInt(60) - 30;
            // 換算弧度
            double theta = jiaodu * Math.PI / 180;

            // 獲得字母數(shù)字
            char c = word.charAt(i);

            // 將c 輸出到圖片
            graphics2d.rotate(theta, x, 20);
            graphics2d.drawString(String.valueOf(c), x, 20);
            graphics2d.rotate(-theta, x, 20);
            x += 30;
        }

        // 將驗證碼內(nèi)容保存session
        request.getSession().setAttribute("checkcode_session", word);

        // 步驟五 繪制干擾線
        graphics.setColor(getRandColor(160, 200));
        int x1;
        int x2;
        int y1;
        int y2;
        for (int i = 0; i < 30; i++) {
            x1 = random.nextInt(width);
            x2 = random.nextInt(12);
            y1 = random.nextInt(height);
            y2 = random.nextInt(12);
            graphics.drawLine(x1, y1, x1 + x2, x2 + y2);
        }

        // 將上面圖片輸出到瀏覽器 ImageIO
        graphics.dispose();// 釋放資源
        
        //將圖片寫到response.getOutputStream()中
        ImageIO.write(bufferedImage, "jpg", response.getOutputStream());

    }

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

    /**
     * 取其某一范圍的color
     * 
     * @param fc
     *            int 范圍參數(shù)1
     * @param bc
     *            int 范圍參數(shù)2
     * @return Color
     */
    private Color getRandColor(int fc, int bc) {
        // 取其隨機顏色
        Random random = new Random();
        if (fc > 255) {
            fc = 255;
        }
        if (bc > 255) {
            bc = 255;
        }
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }

}

2)接著我們就可以在servlet中寫校驗代碼：

//驗證碼校驗
        //獲得頁面輸入的驗證
        String checkCode_client = request.getParameter("checkCode");
        //獲得生成圖片的文字的驗證碼
        String checkCode_session = (String) request.getSession().getAttribute("checkcode_session");
        //比對頁面的和生成圖片的文字的驗證碼是否一致
        if(!checkCode_session.equals(checkCode_client)){
            request.setAttribute("loginInfo", "您的驗證碼不正確");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
            return;
        }
        //獲得頁面的用戶名和密碼進行數(shù)據(jù)庫的校驗
        //...

3)通過在jsp文件頁面中寫代碼將錯誤信息提示顯示在前端

image.png