1. 前言
图形验证码可以让服务器以图片的形式传给客户端，也可以让客户端自己实现。那客户端要怎么做呢？其实很简单，可以使用Android的Canvas、Paint和Random来实现。用Random来随机生成数字、字母、颜色、画笔原点等等，设置Paint的颜色和样式，然后再Canvas上面绘制，这样一个图形验证码就生成好了。
2. 具体实现
根据上面所说的，我们可以封装一个工具类来使用，详细功能有：
- 自定义验证码类型：数字、字母、数字字母组合
- 自定义验证码大小
- 自定义验证码背景颜色
- 自定义干扰线数量
- 自定义字体大小、数量、间距
具体代码如下：
package com.fantasy.blogdemo.captcha;import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;import java.util.Random;/*** 图形验证码工具* <pre>* author : Fantasy* version : 1.0, 2019-06-27* since : 1.0, 2019-06-27* </pre>*/
public class Captcha {private static final char[] CHARS_NUMBER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};private static final char[] CHARS_LETTER = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j','k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w','x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J','K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W','X', 'Y', 'Z'};private static final char[] CHARS_ALL = {'0', '1', '2', '3', '4', '5', '6','7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j','k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w','x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J','K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W','X', 'Y', 'Z'};/*** 验证码图片的宽度*/private int mWidth;/*** 验证码图片的高度*/private int mHeight;private int mBackgroundColor;/*** 验证码的长度*/private int mLength;/*** 干扰线的数量*/private int mLineNumber;private int mFontSize;/*** 字体左边距*/private int mFontPaddingLeft;/*** 字体左边距范围值*/private int mFontPaddingLeftRang;/*** 字体上边距*/private int mFontPaddingTop;/*** 字体上边距范围值*/private int mFontPaddingTopRang;private TYPE mType;private Random mRandom;private static Captcha mInstance;/*** 生成的验证码*/private String mCode;public enum TYPE {NUMBER, LETTER, CHARS}private Captcha() {mType = TYPE.CHARS;mWidth = 200;mHeight = 80;mBackgroundColor = Color.WHITE;mLength = 4;mLineNumber = 2;mFontSize = 50;mFontPaddingLeft = 20;mFontPaddingLeftRang = 20;mFontPaddingTop = 45;mFontPaddingTopRang = 15;mRandom = new Random();}public static Captcha getInstance() {if (mInstance == null) {synchronized (Captcha.class) {mInstance = new Captcha();}}return mInstance;}/*** 设置验证码类型，有：数字、英文字母、数字加英文字母** @param type 类型* @return CaptchaUtils实例*/public Captcha setType(TYPE type) {mType = type;return mInstance;}/*** 设置验证码图片大小** @param width 宽度* @param height 高度* @return CaptchaUtils实例*/public Captcha setSize(int width, int height) {mWidth = width;mHeight = height;return mInstance;}/*** 设置背景颜色** @param color 颜色* @return CaptchaUtils实例*/public Captcha setBackgroundColor(int color) {mBackgroundColor = color;return mInstance;}/*** 设置验证码的长度** @param length 长度* @return CaptchaUtils实例*/public Captcha setLength(int length) {mLength = length;return mInstance;}/*** 设置干扰性数量** @param number 数量* @return CaptchaUtils实例*/public Captcha setLineNumber(int number) {mLineNumber = number;return mInstance;}/*** 设置字体大小** @param size 字体大小* @return CaptchaUtils实例*/public Captcha setFontSize(int size) {mFontSize = size;return mInstance;}/*** 设置字体间距** @param paddingLeft 左边距* @param paddingTop 上边距* @return CaptchaUtils实例*/public Captcha setFontPadding(int paddingLeft, int paddingTop) {mFontPaddingLeft = paddingLeft;mFontPaddingTop = paddingTop;return mInstance;}/*** 设置字体间距** @param paddingLeft 左边距* @param paddingLeftRang 左边距范围值* @param paddingTop 上边距* @param paddingTopRang 上边距范围值* @return CaptchaUtils实例*/public Captcha setFontPadding(int paddingLeft, int paddingLeftRang, int paddingTop,int paddingTopRang) {mFontPaddingLeft = paddingLeft;mFontPaddingLeftRang = paddingLeftRang;mFontPaddingTop = paddingTop;mFontPaddingTopRang = paddingTopRang;return mInstance;}/*** 获取生成的图形验证码** @return 图形验证码的字符串*/public String getCode() {return mCode;}/*** 生成图形验证码** @return 图形验证码的图片*/public Bitmap create() {mCode = createCode();Bitmap bitmap = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);Canvas canvas = new Canvas(bitmap);canvas.drawColor(mBackgroundColor);Paint paint = new Paint();paint.setTextSize(mFontSize);int fontPaddingLeft = 0;for (int i = 0; i < mCode.length(); i++) {getRandomTextStyle(paint);fontPaddingLeft += getRandomFontPaddingLeft();canvas.drawText(String.valueOf(mCode.charAt(i)), fontPaddingLeft, getRandomFontPaddingTop(), paint);}for (int i = 0; i < mLineNumber; i++) {drawLine(canvas, paint);}canvas.save();canvas.restore();return bitmap;}/*** 生成图形验证码** @return 图形验证码的字符串*/private String createCode() {StringBuilder buffer = new StringBuilder();switch (mType) {case NUMBER:for (int i = 0; i < mLength; i++) {buffer.append(CHARS_NUMBER[mRandom.nextInt(CHARS_NUMBER.length)]);}break;case LETTER:for (int i = 0; i < mLength; i++) {buffer.append(CHARS_LETTER[mRandom.nextInt(CHARS_LETTER.length)]);}break;case CHARS:for (int i = 0; i < mLength; i++) {buffer.append(CHARS_ALL[mRandom.nextInt(CHARS_ALL.length)]);}break;default:for (int i = 0; i < mLength; i++) {buffer.append(CHARS_ALL[mRandom.nextInt(CHARS_ALL.length)]);}break;}return buffer.toString();}/*** 获取随机颜色** @return 颜色*/private int getRandomColor() {int red = mRandom.nextInt(256);int green = mRandom.nextInt(256);int blue = mRandom.nextInt(256);return Color.rgb(red, green, blue);}/*** 获取随机文本样式** @param paint 涂料*/private void getRandomTextStyle(Paint paint) {int color = getRandomColor();paint.setColor(color);paint.setFakeBoldText(mRandom.nextBoolean()); // true为粗体，false为非粗体int skewX = mRandom.nextInt(11) / 10;skewX = mRandom.nextBoolean() ? skewX : -skewX;paint.setTextSkewX(skewX); // 负数表示右斜，整数左斜// paint.setUnderlineText(true); // true为下划线，false为非下划线// paint.setStrikeThruText(true); // true为删除线，false为非删除线}/*** 获取随机字体左边距** @return 左边距*/private int getRandomFontPaddingLeft() {return mFontPaddingLeft + mRandom.nextInt(mFontPaddingLeftRang);}/*** 获取随机字体上边距** @return 上边距*/private int getRandomFontPaddingTop() {return mFontPaddingTop + mRandom.nextInt(mFontPaddingTopRang);}/*** 生成干扰性** @param canvas 画布* @param paint 涂料*/private void drawLine(Canvas canvas, Paint paint) {int color = getRandomColor();int startX = mRandom.nextInt(mWidth);int startY = mRandom.nextInt(mHeight);int stopX = mRandom.nextInt(mWidth);int stopY = mRandom.nextInt(mHeight);paint.setStrokeWidth(1);paint.setColor(color);canvas.drawLine(startX, startY, stopX, stopY, paint);}}
3. 使用方式
获取实例并设置
mCaptcha = Captcha.getInstance().setType(Captcha.TYPE.CHARS).setSize(200, 80).setBackgroundColor(Color.WHITE).setLength(4).setLineNumber(2).setFontSize(50).setFontPadding(20, 20, 45, 15);生成图形验证码，并且在ImageView中显示
mIvCaptcha.setImageBitmap(mCaptcha.create());获取验证码的字符串，可用于比对输入是否正确
if (result.equals(mCaptcha.getCode())) {showToast(R.string.captcha_correct);
} else {showToast(R.string.captcha_wrong);
}4. 效果图
想看完整代码可以到我的GitHub上面看看BlogDemo。
如果想进一步交流和学习的同学，可以加一下QQ群哦！
