javaweb实现验证码（来源慕课网）

以下代码为实现验证码的方法：

package imooccode;

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;

/**
* 验证码工具类
*/
public class CaptcahCode {

/**
* 验证生成的方法
* @param response
* @return
*/
public static String drawImage(HttpServletResponse response){
//1:定义以字符串的拼接的StringBuilder
StringBuilder builder = new StringBuilder();
//准备产生4个字符串的随机数
for(int i=0;i<4;i++){
builder.append(randomChar());
}
String code = builder.toString();

//2:定义图片的宽度和高度
int width = 70;
int height = 25;
//简历bufferedImage对象，制定图片的长度和宽度以及色彩
BufferedImage bi = new BufferedImage(width,height,BufferedImage.TYPE_3BYTE_BGR);
//3:获取到 Graphics2D 绘制对象，开始绘制验证码
Graphics2D g = bi.createGraphics();
//4:设置文字的字体和大小
Font font = new Font("微软雅黑",Font.PLAIN,20);
//设置字体的颜色
Color color = new Color(0,0,0);
//设置字体
g.setFont(font);
//设置颜色
g.setColor(color);
//设置背景
g.setBackground(new Color(226,226,240));
//开始绘制对象
g.clearRect(0,0,width,height);
//绘制形状，获取矩形对象
FontRenderContext context = g.getFontRenderContext();
Rectangle2D bounds = font.getStringBounds(code,context);
//计算文件的坐标和间距
double x = (width - bounds.getWidth())/2;
double y = (height - bounds.getHeight())/2;
double ascent = bounds.getY();
double baseY = y - ascent;
g.drawString(code,(int)x,(int)baseY);
//结束绘制
g.dispose();
try {
ImageIO.write(bi,"jpg",response.getOutputStream());
//刷新响应流
response.flushBuffer();
}catch(Exception ex){
ex.printStackTrace();
}

return code;
}

/**
* 算术表达式验证码
*
* 1：干扰线的产生
* 2: 范围随机颜色，随机数
*
* @param response
* @return
*/
public static  String drawImageVerificate(HttpServletResponse response){
//定义验证码的宽度和高度
int width = 100,height = 30;
//在内存中创建图片
BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
//创建图片的上下文
Graphics2D g = image.createGraphics();
//产生随机对象,此随机对象主要用于算术表达式的数字
Random random = new Random();
//设置背景
g.setColor(getRandomColor(240,250));
//设置字体
g.setFont(new Font("微软雅黑", Font.PLAIN,22));
//开始绘制
g.fillRect(0,0,width,height);

//干扰线的绘制，绘制线条到图片中
g.setColor(getRandomColor(180,230));
for(int i=0;i<10;i++){
int x = random.nextInt(width);
int y = random.nextInt(height);
int x1 = random.nextInt(60);
int y1 = random.nextInt(60);
g.drawLine(x,y,x1,y1);
}

//开始进行对算术验证码表达式的拼接
int num1 = (int)(Math.random()*10 + 1);
int num2 = (int)(Math.random()*10 + 1);
int fuhao = random.nextInt(3);//产生一个[0,2]之间的随机整数
//记录符号
String fuhaostr = null;
int result = 0;
switch (fuhao){
case 0 : fuhaostr = "+";result = num1 + num2;break;
case 1: fuhaostr = "-";result = num1 - num2;break;
case 2 : fuhaostr = "*";result = num1 * num2;break;
//case 3 : fuhaostr = "/";result = num1 / num2;break;
}
//拼接算术表达式,用户图片显示。
String calc = num1 + " " + fuhaostr +" "+ num2 +" = ?";
//设置随机颜色
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
//绘制表达式
g.drawString(calc,5,25);
//结束绘制
g.dispose();
try {
//输出图片到页面
ImageIO.write(image,"JPEG",response.getOutputStream());
return String.valueOf(result);
}catch (Exception ex){
ex.printStackTrace();
return null;
}
}

/**
* 范围随机颜色
* @param fc
* @param bc
* @return
*/
public static Color getRandomColor(int fc,int bc){
//利用随机数
Random random  = new Random();
//随机颜色,了解颜色-Color(red,green,blue).rgb三元色 0-255
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);
}

/**
* 此方法用户产生随机数字母和数字
* @return
*/
private static char randomChar(){
//1:定义验证需要的字母和数字
String string = "QWERTYUIOPASDFGHJKLZXCVBNM0123456789";
//2：定义随机对象
Random random = new Random();
return string.charAt(random.nextInt(string.length()));
//random.nextint的用法是将在string.lenth的范围内随机生成一位数，而charat函数是提取string字符串中对应位置的数
}

}

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