本文内容大多基于官方文档和网上前辈经验总结，经过个人实践加以整理积累，仅供参考。
1 生成随机字符串
/**
* 系统默认字符源：大小写字母和数字，去掉了[0,1,l,o,I,O]这几个容易混淆的字符
*/
private static final String CAPTCHA_SOURCES =
"23456789abcdefghijkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";
/**
* 使用系统默认字符源生成验证码
* @param size 验证码长度
* @return
*/
public static String
generateCaptcha(
int size) {
return generateCaptcha(size, CAPTCHA_SOURCES);
}
/**
* 使用指定字符源生成验证码
* @param size 验证码长度
* @param sources 验证码字符源
* @return
*/
public static String
generateCaptcha(
int size, String sources) {
if (sources ==
null || sources.length() ==
0) {
sources = CAPTCHA_SOURCES;
}
int sourcesLength = sources.length();
Random random =
new Random(System.currentTimeMillis());
StringBuilder captcha =
new StringBuilder();
for (
int i =
0; i < size; i++) {
captcha.append(sources.charAt(random.nextInt(sourcesLength -
1)));
}
return captcha.toString();
}
单元测试：
@Test
public void test() {
System
.out.println(CaptchaUtil
.generateCaptcha(
4))
System
.out.println(CaptchaUtil
.generateCaptcha(
6))
System
.out.println(CaptchaUtil
.generateCaptcha(
4,
"!@#$%&?"))
}
测试结果：
PbFd
yV5ycy
&@
!!
2 输出特定字符串的图像文件
/**
* 指定验证码字体
*/
private static final String FONT =
"Calibri";
/**
* 输出特定字符串的图像文件输出流
* @param width 验证码图片宽度
* @param height 验证码图片高度
* @param outputStream 验证码图片文件输出流
* @param captcha 验证码文本字符串
* @throws IOException
*/
public static void outputImage(
int width,
int height, OutputStream outputStream, String captcha)
throws IOException {
int size = captcha.length();
BufferedImage image =
new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Random random =
new Random();
Graphics2D g2d = image.createGraphics();
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
Color[] colors =
new Color[
5];
Color[] colorSpaces =
new Color[] {
Color.WHITE, Color.CYAN, Color.GRAY, Color.LIGHT_GRAY, Color.MAGENTA, Color.ORANGE, Color.PINK, Color.YELLOW
};
float[] fractions =
new float[colors.length];
for (
int i =
0; i < colors.length; i++) {
colors[i] = colorSpaces[random.nextInt(colorSpaces.length)];
fractions[i] = random.nextFloat();
}
Arrays.sort(fractions);
g2d.setColor(getRandomColor(
100,
160));
int fontSize = height -
8;
Font font =
new Font(FONT, Font.ITALIC, fontSize);
g2d.setFont(font);
char[] chars = captcha.toCharArray();
for (
int i =
0; i < size; i++) {
AffineTransform affine =
new AffineTransform();
affine.setToRotation(
Math.PI /
5 * random.nextDouble() * (random.nextBoolean() ?
1 : -
1),
(width / size) * i + fontSize /
2,
height /
2);
g2d.setTransform(affine);
g2d.drawChars(chars, i,
1, ((width -
10) / size) * i +
5, height /
2 + fontSize /
2 -
6);
}
g2d.dispose();
ImageIO.write(image,
"jpg", outputStream);
}
/**
* 输出特定字符串的图像文件
* @param width 验证码图片宽度
* @param height 验证码图片高度
* @param outputFile 验证码图片文件
* @param captcha 验证码文本字符串
* @throws IOException
*/
public static void outputImage(
int width,
int height, File outputFile, String captcha)
throws IOException {
if (outputFile !=
null) {
File dir = outputFile.getParentFile();
if (!dir.exists()) {
dir.mkdirs();
}
try {
outputFile.createNewFile();
FileOutputStream fos =
new FileOutputStream(outputFile);
outputImage(width, height, fos, captcha);
}
catch (IOException e) {
throw e;
}
}
}
private static Color
getRandomColor(
int fc,
int bc) {
if (fc >
255) {
fc =
255;
}
if (bc >
255) {
bc =
255;
}
Random random =
new Random();
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);
}
单元测试：
@Test
public void test()
throws FileNotFoundException, IOException {
CaptchaUtil.outputImage(
400,
200,
new FileOutputStream(
"D:/captcha.jpg"),
"X4u9");
}
测试生成的验证码图片：
3 生成验证码文件并返回验证码文本字符串
/**
* 生成验证码文件并返回验证码文本字符串
* @param width 验证码图片宽度
* @param height 验证码图片高度
* @param outputFile 验证码图片文件
* @param size 验证码长度
* @return 验证码文本字符串
* @throws IOException
*/
public static String
outputCaptchaImage(
int width,
int height, File outputFile,
int size)
throws IOException {
String captcha = generateCaptcha(size);
outputImage(width, height, outputFile, captcha);
return captcha;
}
/**
* 生成验证码文件输出流并返回验证码文本字符串
* @param width 验证码图片宽度
* @param height 验证码图片高度
* @param outputStream 验证码图片文件
* @param size 验证码长度
* @return 验证码文本字符串
* @throws IOException
*/
public static String
outputCaptchaImage(
int width,
int height, OutputStream outputStream,
int size)
throws IOException {
String captcha = generateCaptcha(size);
outputImage(width, height, outputStream, captcha);
return captcha;
}
单元测试：
@Test
public void test()
throws FileNotFoundException, IOException {
CaptchaUtil.outputCaptchaImage(
400,
200,
new File(
"D:/captcha.jpg"),
5);
}
测试生成的验证码图片：
4 增强验证码图片识别难度
重写以下方法
public static void outputImage(
int width,
int height, OutputStream outputStream, String captcha)
throws IOException {
int size = captcha.length();
BufferedImage image =
new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Random random =
new Random();
Graphics2D g2d = image.createGraphics();
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
Color[] colors =
new Color[
5];
Color[] colorSpaces =
new Color[] {
Color.WHITE, Color.CYAN, Color.GRAY, Color.LIGHT_GRAY, Color.MAGENTA, Color.ORANGE, Color.PINK, Color.YELLOW
};
float[] fractions =
new float[colors.length];
for (
int i =
0; i < colors.length; i++) {
colors[i] = colorSpaces[random.nextInt(colorSpaces.length)];
fractions[i] = random.nextFloat();
}
Arrays.sort(fractions);
g2d.setColor(Color.GRAY);
g2d.fillRect(
0,
0, width, height);
Color color = getRandomColor(
200,
250);
g2d.setColor(color);
g2d.fillRect(
0,
2, width, height -
4);
random =
new Random();
g2d.setColor(getRandomColor(
160,
200));
for (
int i =
0; i <
20; i++) {
int x = random.nextInt(width -
1);
int y = random.nextInt(height -
1);
int x1 = random.nextInt(
6) +
1;
int y1 = random.nextInt(
12) +
1;
g2d.drawLine(x, y, x + x1 +
40, y + y1 +
20);
}
float noiseRatio =
0.05f;
int area = (
int) (noiseRatio * width * height);
for (
int i =
0; i < area; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int rgb = getRandomIntColor();
image.setRGB(x, y, rgb);
}
shear(g2d, width, height, color);
g2d.setColor(getRandomColor(
100,
160));
int fontSize = height -
8;
Font font =
new Font(FONT, Font.ITALIC, fontSize);
g2d.setFont(font);
char[] chars = captcha.toCharArray();
for (
int i =
0; i < size; i++) {
AffineTransform affine =
new AffineTransform();
affine.setToRotation(
Math.PI /
5 * random.nextDouble() * (random.nextBoolean() ?
1 : -
1),
(width / size) * i + fontSize /
2,
height /
2);
g2d.setTransform(affine);
g2d.drawChars(chars, i,
1, ((width -
10) / size) * i +
5, height /
2 + fontSize /
2 -
6);
}
g2d.dispose();
ImageIO.write(image,
"jpg", outputStream);
}
private static int getRandomIntColor() {
int[] rgb = getRandomRgb();
int color =
0;
for (
int c : rgb) {
color = color <<
8;
color = color | c;
}
return color;
}
private static int[]
getRandomRgb() {
int[] rgb =
new int[
3];
for (
int i =
0; i <
3; i++) {
rgb[i] =
new Random().nextInt(
255);
}
return rgb;
}
private static void shear(Graphics g,
int width,
int height, Color color) {
shearX(g, width, height, color);
shearY(g, width, height, color);
}
private static void shearX(Graphics g,
int width,
int height, Color color) {
Random random =
new Random();
int period = random.nextInt(
2);
boolean borderGap =
true;
int frames =
1;
int phase = random.nextInt(
2);
for (
int i =
0; i < height; i++) {
double d = (
double) (period >>
1)
* Math.sin((
double) i / (
double) period
+ (
6.2831853071795862D * (
double) phase)
/ (
double) frames);
g.copyArea(
0, i, width,
1, (
int) d,
0);
if (borderGap) {
g.setColor(color);
g.drawLine((
int) d, i,
0, i);
g.drawLine((
int) d + width, i, width, i);
}
}
}
private static void shearY(Graphics g,
int width,
int height, Color color) {
Random random =
new Random();
int period = random.nextInt(
40) +
10;
boolean borderGap =
true;
int frames =
20;
int phase =
7;
for (
int i =
0; i < width; i++) {
double d = (
double) (period >>
1)
* Math.sin((
double) i / (
double) period
+ (
6.2831853071795862D * (
double) phase)
/ (
double) frames);
g.copyArea(i,
0,
1, height,
0, (
int) d);
if (borderGap) {
g.setColor(color);
g.drawLine(i, (
int) d, i,
0);
g.drawLine(i, (
int) d + height, i, height);
}
}
}
单元测试生成的验证码图片：
5 编写生成验证码图片的Servlet
import java.io.IOException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class CaptchaGenerator extends HttpServlet {
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException {
doPost(request, response);
}
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws IOException {
response.setHeader(
"Pragma",
"No-cache");
response.setHeader(
"Cache-Control",
"no-cache");
response.setDateHeader(
"Expires",
0);
response.setContentType(
"image/jpeg");
String captcha = CaptchaUtil.generateCaptcha(
5);
HttpSession session = request.getSession(
true);
session.setAttribute(
"captcha", captcha.toLowerCase());
CaptchaUtil.outputImage(
400,
200, response.getOutputStream(), captcha);
}
}
6 配置生成验证码图片的Servlet
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID"
version="3.1">
<display-name>Captcha
</display-name>
<welcome-file-list>
<welcome-file>index.jsp
</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>captchaGenerator
</servlet-name>
<servlet-class>CaptchaGenerator
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>captchaGenerator
</servlet-name>
<url-pattern>/refresh_captcha.ajax
</url-pattern>
</servlet-mapping>
</web-app>
7 编写 JSP 页面
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=Edge">
<title>Hello Captcha
</title>
</head>
<body>
The is Captcha Image:
<br>
<img src="refresh_captcha.ajax">
</body>
</html>
运行后页面：
