這是我的第一篇java學習，主要是爲了記錄我學習Java的心路歷程，爲了就業做準備。
javaWeb應用產生驗證碼主要分爲三個板塊，即：1，產生驗證碼字符串，字符串寫入到輸出流中。2，在code.jsp中進行中間處理，主要是讓瀏覽器清空緩存。 3，在index.jsp頁面生成驗證碼
1，產生驗證碼字符串都工具類
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 {
//這是生成單個隨機字符的方法
public static char randomChar(){
String str = "asdfghjkl123456";
Random random = new Random();
return str.charAt(random.nextInt(str.length()));
}
//這是生成驗證碼的方法
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);
//上面是一個緩衝流
Graphics2D graphics2D = bi.createGraphics();
graphics2D.setBackground(new Color(226,226,200));
graphics2D.setColor(new Color(255,255,255));
//Font類的構造函數由Font(字體名稱，style,size)
Font font = new Font("微軟雅黑",Font.PLAIN,20);
graphics2D.setFont(font);
graphics2D.clearRect(0,0,width,height);//這條是使用當前會圖表的背景色來填充矩形區域
//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();//這條語句是我最懵逼的呢，我沒搞懂他是什麼意思
double baseY = y-ascent;
graphics2D.drawString(code,(int)x,(int)baseY);
//結束繪製
graphics2D.dispose();
try{
ImageIO.write(bi,"jpg",response.getOutputStream());
}catch (Exception e){
e.printStackTrace();
}
return code;
}
}
2.在code.jsp中通過工具類生成驗證碼
<%@ 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" %>
<%
/**
* 以下三條代碼都是用來清空瀏覽器緩存的，我也不知道是什麼意思
*/
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);
//下面兩條代碼用來解決getOutputStream異常，如果沒有這兩行代碼，驗證碼無法顯示
//然而我也不知道是什麼意思
out.clear();
out = pageContext.pushBody();
%>
3,在index.jsp中顯示驗證碼
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<img src="code.jsp" >
</body>
</html>
