这是我的第一篇java学习，主要是为了记录我学习Java的心路历程，为了就业做准备。
javaWeb应用产生验证码主要分为三个板块，即：1，产生验证码字符串，字符串写入到输出流中。2，在code.jsp中进行中间处理，主要是让浏览器清空缓存。 3，在index.jsp页面生成验证码
1，产生验证码字符串都工具类
package com.imooc.skr;
import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.font.FontRenderContext;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import java.util.Random;
public class CaptchaCode {
//这是生成单个随机字符的方法
public static char randomChar(){
String str = "asdfghjkl123456";
Random random = new Random();
return str.charAt(random.nextInt(str.length()));
}
//这是生成验证码的方法
public static String drawImage(HttpServletResponse response){
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < 4; i++) {
stringBuilder.append(randomChar());
}
String code = stringBuilder.toString();
int width = 120;
int height = 25;
BufferedImage bi = new BufferedImage(width,height,BufferedImage.TYPE_3BYTE_BGR);
//上面是一个缓冲流
Graphics2D graphics2D = bi.createGraphics();
graphics2D.setBackground(new Color(226,226,200));
graphics2D.setColor(new Color(255,255,255));
//Font类的构造函数由Font(字体名称，style,size)
Font font = new Font("微软雅黑",Font.PLAIN,20);
graphics2D.setFont(font);
graphics2D.clearRect(0,0,width,height);//这条是使用当前会图表的背景色来填充矩形区域
//好像用graphics2D.fillRect()也可以
FontRenderContext context = graphics2D.getFontRenderContext();
Rectangle2D bounds = font.getStringBounds(code,context);
double x = (width-bounds.getWidth())/2;
double y = (height-bounds.getHeight())/2;
double ascent = bounds.getY();//这条语句是我最懵逼的呢，我没搞懂他是什么意思
double baseY = y-ascent;
graphics2D.drawString(code,(int)x,(int)baseY);
//结束绘制
graphics2D.dispose();
try{
ImageIO.write(bi,"jpg",response.getOutputStream());
}catch (Exception e){
e.printStackTrace();
}
return code;
}
}
2.在code.jsp中通过工具类生成验证码
<%@ page import="com.imooc.skr.CaptchaCode" %><%--
Created by IntelliJ IDEA.
User: finajoy
Date: 2019/12/30
Time: 11:09
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%
/**
* 以下三条代码都是用来清空浏览器缓存的，我也不知道是什么意思
*/
response.setHeader("pragma","no-cache");
response.setHeader("cache-control","no-cache");
response.setHeader("expires","no-cache");
String code = CaptchaCode.drawImage(response);
session.setAttribute("code",code);
//下面两条代码用来解决getOutputStream异常，如果没有这两行代码，验证码无法显示
//然而我也不知道是什么意思
out.clear();
out = pageContext.pushBody();
%>
3,在index.jsp中显示验证码
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<img src="code.jsp" >
</body>
</html>
