2种servlet 里面的验证码书写方法

1 直接写在servlet里面

package com.itheima.web;

import javax.imageio.ImageIO;
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 java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

//用来获取验证码的.
//1. 把验证码以图片的形式展示到: login.jsp页面中.
//2. 把验证码存储到 session容器中.
@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //  创建画布
        int width = 120;
        int height = 40;
        BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //  获得画笔
        Graphics g = bufferedImage.getGraphics();
        //  填充背景颜色
        g.setColor(Color.white);
        g.fillRect(0, 0, width, height);
        //  绘制边框
        g.setColor(Color.red);
        g.drawRect(0, 0, width - 1, height - 1);
        //  生成随机字符
        //  准备数据
        String data = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
        //  准备随机对象
        Random r = new Random();
        //  声明一个变量 保存验证码
        String code = "";
        //  书写4个随机字符
        for (int i = 0; i < 4; i++) {
            //  设置字体
            g.setFont(new Font("宋体", Font.BOLD, 28));
            //  设置随机颜色
            g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));

            String str = data.charAt(r.nextInt(data.length())) + "";
            g.drawString(str, 10 + i * 28, 30);

            //  将新的字符 保存到验证码中
            code = code + str;
        }
        //  绘制干扰线
        for (int i = 0; i < 6; i++) {
            //  设置随机颜色
            g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));

            g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));
        }

        //  将验证码 打印到控制台
        System.out.println(code);

        //  将验证码放到session中
        request.getSession().setAttribute("code", code);

        //  将画布显示在浏览器中
        ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
    }

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

}

2 写在jsp里面

<%@page import="java.io.FileOutputStream"%>
<%@ page contentType="text/html; charset=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 = 130, height = 39; // 图片宽度和高度
	// 创建用于保存图片信息的缓冲区对象
	BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
	Graphics g = image.getGraphics(); // 获取画笔
	g.setColor(new Color(0xffffff)); // 设置画笔颜色
	g.fillRect(0, 0, width, height); // 填充背景颜色
	Random r = new Random(); // 创建随机数对象
	// 添加干扰项
	for(int i = 0; i < 15; i++) {
		g.setFont(new Font("Candara", Font.ITALIC, 20)); // 设置字体
		g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255))); // 重新设置画笔颜色
		g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));
	}
	String data = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM0123456789";
	int length = data.length();
	String capstr = "";
	g.setFont(new Font("Candara", Font.BOLD, 35)); // 设置字体
	for(int i = 0; i < 4; i++) {
		int index = r.nextInt(length);
		String str = data.charAt(index) + "";
		capstr += str;
		g.setColor(new Color(r.nextInt(150), r.nextInt(150), r.nextInt(150))); // 重新设置画笔颜色
		g.drawString(str, 10+(i*28), 30); // 将字符写入图片
	}
	
	g.dispose(); // 释放资源
	response.setContentType("image/jpeg"); // 设置响应类型
	out.clear(); // 清空缓冲区中的字符流数据(字符流和字节流不能同时使用，否则会抛异常)
	
	OutputStream strm = response.getOutputStream(); // 输出流
	ImageIO.write(image, "jpeg", strm); // 将图片写到输出流
	strm.close(); // 关闭输出流
	
	session.setAttribute("code_session", capstr); // 保存验证码到session中，用于登录校验
%>