icu.easyj.core.util.Base64Utils Maven / Gradle / Ivy

/*
 * Copyright 2021 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package icu.easyj.core.util;

import java.nio.charset.StandardCharsets;

import org.springframework.lang.NonNull;
import org.springframework.util.Assert;

/**
 * Base64工具类
 *
 * @author wangliang181230
 */
public abstract class Base64Utils {

	/**
	 * Base64字符在Assic码
	 */
	public static final byte[] BASE64_CHAR_TABLE = {
			// 0 1 2 3 4 5 6 7 8 9 A B C D E F
			-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0F
			-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1F
			-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 43, -1, -1, -1, 47, // 20-2F（含：+ /）
			48, 49, 50, 51, 52, 53, 54, 55, 56, 57, -1, -1, -1, -1, -1, -1, // 30-3F（含：0-9）
			-1, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, // 40-4F（含：大写A~大写O）
			80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, -1, -1, -1, -1, -1, // 50-5F（含：大写P~大写Z）
			-1, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, // 60-6F（含：小写a~小写o）
			112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122 // 70-7A（含：小写p-小写z）
	};

	/**
	 * 补位字符
	 */
	public static final char PADDING_CHAR = '=';

	/**
	 * 规范化Base64串.
	 *
	 * @param base64Str Base64字符串
	 * @return 规范化后的Base64串
	 * @throws IllegalArgumentException 编码有误
	 */
	@NonNull
	public static String normalize(@NonNull String base64Str) throws IllegalArgumentException {
		Assert.notNull(base64Str, "'base64Str' must not be null");

		boolean needToChange = false;

		int base64Length = base64Str.length();
		StringBuilder sb = new StringBuilder(base64Length > 500 ? base64Length / 2 : base64Length);

		int i = 0;
		char c;
		byte[] bytes = null;
		int pos;
		String hex;
		int v;
		while (i < base64Length) {
			c = base64Str.charAt(i);
			switch (c) {
				// 空格 -> `+`
				case ' ':
					sb.append('+');
					i++;
					needToChange = true;
					break;
				// 移除回车符、换行符、双引号（部分前端方法经常会生效带双引号的Base64串）
				case '\r':
				case '\n':
				case '\"':
					i++;
					needToChange = true;
					break;
				// URL编码16进制字符转换
				case '%':
					try {
						if (bytes == null) {
							bytes = new byte[(base64Length - i) / 3];
						}

						pos = 0;
						while (c == '%' && i + 2 < base64Length) {
							hex = base64Str.substring(i + 1, i + 3);
							v = Integer.parseInt(hex, 16);
							if (v < 0) {
								throw new IllegalArgumentException("转义（%）模式时存在非法十六进制字符-负值: %" + hex + " -> " + v);
							}
							bytes[pos++] = (byte)v;
							i += 3;
							if (i < base64Length) {
								c = base64Str.charAt(i);
							}
						}

						if (c == '%' && i < base64Length) {
							throw new IllegalArgumentException("不完整的转义（%）模式");
						}

						sb.append(new String(bytes, 0, pos, StandardCharsets.UTF_8));
					} catch (NumberFormatException e) {
						throw new IllegalArgumentException("转义（%）模式中的非法十六进制字符 - " + e.getMessage());
					}
					needToChange = true;
					break;
				default:
					sb.append(c);
					i++;
					break;
			}
		}

		return (needToChange ? sb.toString() : base64Str);
	}

	/**
	 * 判断是否为Base64字符（除'='号外）
	 *
	 * @param c 字符
	 * @return 是否为Base64字符
	 */
	private static boolean isBase64CharInner(char c) {
		return c < BASE64_CHAR_TABLE.length && BASE64_CHAR_TABLE[c] != -1;
	}

	/**
	 * 判断是否为Base64字节（除'='号外）
	 *
	 * @param b 字节
	 * @return 是否为Base64字节
	 */
	private static boolean isBase64CharInner(byte b) {
		return b >= 0 && b < BASE64_CHAR_TABLE.length && BASE64_CHAR_TABLE[b] != -1;
	}

	/**
	 * 判断是否为Base64字符
	 *
	 * @param c 字符
	 * @return 是否为Base64字符
	 */
	public static boolean isBase64Char(char c) {
		return c == PADDING_CHAR || isBase64CharInner(c);
	}

	/**
	 * 判断是否为Base64字节
	 *
	 * @param b 字节
	 * @return 是否为Base64字节
	 */
	public static boolean isBase64Code(byte b) {
		return b == PADDING_CHAR || isBase64CharInner(b);
	}

	/**
	 * 判断是否为Base64字符串
	 *
	 * @param str 字符串
	 * @return 是否为Base64字符串
	 */
	public static boolean isBase64(final CharSequence str) {
		if (str == null || str.length() < 2) {
			return false;
		}

		final char[] charArr = StringUtils.toCharArrayWithoutCopy(str);

		// 计算需校验字符的长度，减掉末尾补位字符数量
		int length = charArr.length;
		if (charArr[length - 1] == PADDING_CHAR) {
			// 存在补位字符时，长度必须为4的倍数
			if (str.length() % 4 != 0) {
				return false;
			}

			--length;
			// 最多末尾两个'='
			if (charArr[length - 1] == PADDING_CHAR) {
				--length;
			}
		} else {
			// 不存在补位字符时，长度除4的余数不能为1
			if (str.length() % 4 == 1) {
				return false;
			}
		}

		// 校验除最后两位的字符
		char c;
		for (int i = 0; i < length; ++i) {
			c = charArr[i];
			if (!isBase64CharInner(c)) {
				return false;
			}
		}

		return true;
	}
}