这个问题真心想不明白？ - 黑马程序员技术交流社区

package com.response;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.PrintWriter;
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;
public class Demo2 extends HttpServlet {
public static final int WIDTH=120;//设置图像的宽
public static final int HEIGHT=25;//设置图像的高
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
//输出注册时候的随机图片
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//BufferedImage 可以自动生成图像，BufferedImage.TYPE_INT_RGB是图片的类型
BufferedImage image=new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
//得到这个图形
Graphics g=image.getGraphics();
//1.设置图像的背景色
setBackaground(g);
//2.设置图像的边框
setBorder(g);
//3.在图像上画干扰线
drawRandomLine(g);
//4.在图像上写随机数
drawRanderNum((Graphics2D)g);
//5.把图像写给浏览器,设置浏览器打开文件的格式
response.setContentType("image/jpeg");
//发响应头控制浏览器不要缓存
response.setDateHeader("expries", -1);
response.setHeader("Cache-Control","no-cache");
response.setHeader("Pragma","no-cache");
ImageIO.write(image, "jpg", response.getOutputStream());
}
private void drawRanderNum(Graphics2D g) {
g.setColor(Color.RED);//设置字的颜色为红色
g.setFont(new Font("宋体",Font.BOLD,20));//设置字体的样式，Font.BOLD为加粗，20字体的高度
int x=10;
for(int i=0;i<4;i++)
{
int degree=new Random().nextInt()%30;//定义字符旋转多少度，%30是表示度数为-30到30度
String shu=new Random().nextInt(10)+"";
g.rotate(degree*Math.PI/180, x, 20);//设置旋转的弧度，后两个参数是基于那个点旋转
g.drawString(shu , x, 20);//这是往图片上写入数字，参数是写入数字的坐标
g.rotate(-degree*Math.PI/180, x, 20);//清掉上次的旋转，确保下次的旋转正确
x=x+30;
}
}
private void drawRandomLine(Graphics g) {
g.setColor(Color.GREEN);//设置干扰线的颜色
for(int i=0;i<5;i++)//i为干扰线的条数
{
int x1=new Random().nextInt(WIDTH);//x1,y1为干扰线的起点的坐标，x坐标必须在图像的宽内，y坐标在高之内
int y1=new Random().nextInt(HEIGHT);
int x2=new Random().nextInt(WIDTH);
int y2=new Random().nextInt(HEIGHT);
g.drawLine(x1, y1, x2, y2);//这个方法是画出干扰线
}
}
private void setBorder(Graphics g) {
g.setColor(Color.BLUE);//？这里为什么只变的是边框
g.drawRect(1, 1, WIDTH-2, HEIGHT-2);
}
private void setBackaground(Graphics g) {
g.setColor(Color.WHITE);//设置图形的背景色为白色
g.fillRect(0, 0, WIDTH, HEIGHT);//填充矩形
}
}

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