一、前言
关于fastjson的com.alibaba.fastjson.util.Base64实现base64解密算法,分别对char[]、字符串进行解密为二进制数组,具体参见如下代码示例。
二、源码说明
package com.alibaba.fastjson.util;@b@@b@import java.util.Arrays;@b@@b@ @b@public class Base64 {@b@@b@ public static final char[] CA = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();@b@ public static final int[] IA = new int[256];@b@ static {@b@ Arrays.fill(IA, -1);@b@ for (int i = 0, iS = CA.length; i < iS; i++)@b@ IA[CA[i]] = i;@b@ IA['='] = 0;@b@ }@b@@b@ /**@b@ * Decodes a BASE64 encoded char array that is known to be resonably well formatted. The method is about twice as@b@ * fast as #decode(char[]). The preconditions are:<br>@b@ * + The array must have a line length of 76 chars OR no line separators at all (one line).<br>@b@ * + Line separator must be "\r\n", as specified in RFC 2045 + The array must not contain illegal characters within@b@ * the encoded string<br>@b@ * + The array CAN have illegal characters at the beginning and end, those will be dealt with appropriately.<br>@b@ *@b@ * @param chars The source array. Length 0 will return an empty array. <code>null</code> will throw an exception.@b@ * @return The decoded array of bytes. May be of length 0.@b@ */@b@ public static byte[] decodeFast(char[] chars, int offset, int charsLen) {@b@ // Check special case@b@ if (charsLen == 0) {@b@ return new byte[0];@b@ }@b@@b@ int sIx = offset, eIx = offset + charsLen - 1; // Start and end index after trimming.@b@@b@ // Trim illegal chars from start@b@ while (sIx < eIx && IA[chars[sIx]] < 0)@b@ sIx++;@b@@b@ // Trim illegal chars from end@b@ while (eIx > 0 && IA[chars[eIx]] < 0)@b@ eIx--;@b@@b@ // get the padding count (=) (0, 1 or 2)@b@ int pad = chars[eIx] == '=' ? (chars[eIx - 1] == '=' ? 2 : 1) : 0; // Count '=' at end.@b@ int cCnt = eIx - sIx + 1; // Content count including possible separators@b@ int sepCnt = charsLen > 76 ? (chars[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;@b@@b@ int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes@b@ byte[] bytes = new byte[len]; // Preallocate byte[] of exact length@b@@b@ // Decode all but the last 0 - 2 bytes.@b@ int d = 0;@b@ for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {@b@ // Assemble three bytes into an int from four "valid" characters.@b@ int i = IA[chars[sIx++]] << 18 | IA[chars[sIx++]] << 12 | IA[chars[sIx++]] << 6 | IA[chars[sIx++]];@b@@b@ // Add the bytes@b@ bytes[d++] = (byte) (i >> 16);@b@ bytes[d++] = (byte) (i >> 8);@b@ bytes[d++] = (byte) i;@b@@b@ // If line separator, jump over it.@b@ if (sepCnt > 0 && ++cc == 19) {@b@ sIx += 2;@b@ cc = 0;@b@ }@b@ }@b@@b@ if (d < len) {@b@ // Decode last 1-3 bytes (incl '=') into 1-3 bytes@b@ int i = 0;@b@ for (int j = 0; sIx <= eIx - pad; j++)@b@ i |= IA[chars[sIx++]] << (18 - j * 6);@b@@b@ for (int r = 16; d < len; r -= 8)@b@ bytes[d++] = (byte) (i >> r);@b@ }@b@@b@ return bytes;@b@ }@b@@b@ public static byte[] decodeFast(String chars, int offset, int charsLen) {@b@ // Check special case@b@ if (charsLen == 0) {@b@ return new byte[0];@b@ }@b@@b@ int sIx = offset, eIx = offset + charsLen - 1; // Start and end index after trimming.@b@@b@ // Trim illegal chars from start@b@ while (sIx < eIx && IA[chars.charAt(sIx)] < 0)@b@ sIx++;@b@@b@ // Trim illegal chars from end@b@ while (eIx > 0 && IA[chars.charAt(eIx)] < 0)@b@ eIx--;@b@@b@ // get the padding count (=) (0, 1 or 2)@b@ int pad = chars.charAt(eIx) == '=' ? (chars.charAt(eIx - 1) == '=' ? 2 : 1) : 0; // Count '=' at end.@b@ int cCnt = eIx - sIx + 1; // Content count including possible separators@b@ int sepCnt = charsLen > 76 ? (chars.charAt(76) == '\r' ? cCnt / 78 : 0) << 1 : 0;@b@@b@ int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes@b@ byte[] bytes = new byte[len]; // Preallocate byte[] of exact length@b@@b@ // Decode all but the last 0 - 2 bytes.@b@ int d = 0;@b@ for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {@b@ // Assemble three bytes into an int from four "valid" characters.@b@ int i = IA[chars.charAt(sIx++)] << 18 | IA[chars.charAt(sIx++)] << 12 | IA[chars.charAt(sIx++)] << 6 | IA[chars.charAt(sIx++)];@b@@b@ // Add the bytes@b@ bytes[d++] = (byte) (i >> 16);@b@ bytes[d++] = (byte) (i >> 8);@b@ bytes[d++] = (byte) i;@b@@b@ // If line separator, jump over it.@b@ if (sepCnt > 0 && ++cc == 19) {@b@ sIx += 2;@b@ cc = 0;@b@ }@b@ }@b@@b@ if (d < len) {@b@ // Decode last 1-3 bytes (incl '=') into 1-3 bytes@b@ int i = 0;@b@ for (int j = 0; sIx <= eIx - pad; j++)@b@ i |= IA[chars.charAt(sIx++)] << (18 - j * 6);@b@@b@ for (int r = 16; d < len; r -= 8)@b@ bytes[d++] = (byte) (i >> r);@b@ }@b@@b@ return bytes;@b@ }@b@@b@ /**@b@ * Decodes a BASE64 encoded string that is known to be resonably well formatted. The method is about twice as fast@b@ * as decode(String). The preconditions are:<br>@b@ * + The array must have a line length of 76 chars OR no line separators at all (one line).<br>@b@ * + Line separator must be "\r\n", as specified in RFC 2045 + The array must not contain illegal characters within@b@ * the encoded string<br>@b@ * + The array CAN have illegal characters at the beginning and end, those will be dealt with appropriately.<br>@b@ *@b@ * @param s The source string. Length 0 will return an empty array. <code>null</code> will throw an exception.@b@ * @return The decoded array of bytes. May be of length 0.@b@ */@b@ public static byte[] decodeFast(String s) {@b@ // Check special case@b@ int sLen = s.length();@b@ if (sLen == 0) {@b@ return new byte[0];@b@ }@b@@b@ int sIx = 0, eIx = sLen - 1; // Start and end index after trimming.@b@@b@ // Trim illegal chars from start@b@ while (sIx < eIx && IA[s.charAt(sIx) & 0xff] < 0)@b@ sIx++;@b@@b@ // Trim illegal chars from end@b@ while (eIx > 0 && IA[s.charAt(eIx) & 0xff] < 0)@b@ eIx--;@b@@b@ // get the padding count (=) (0, 1 or 2)@b@ int pad = s.charAt(eIx) == '=' ? (s.charAt(eIx - 1) == '=' ? 2 : 1) : 0; // Count '=' at end.@b@ int cCnt = eIx - sIx + 1; // Content count including possible separators@b@ int sepCnt = sLen > 76 ? (s.charAt(76) == '\r' ? cCnt / 78 : 0) << 1 : 0;@b@@b@ int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes@b@ byte[] dArr = new byte[len]; // Preallocate byte[] of exact length@b@@b@ // Decode all but the last 0 - 2 bytes.@b@ int d = 0;@b@ for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {@b@ // Assemble three bytes into an int from four "valid" characters.@b@ int i = IA[s.charAt(sIx++)] << 18 | IA[s.charAt(sIx++)] << 12 | IA[s.charAt(sIx++)] << 6@b@ | IA[s.charAt(sIx++)];@b@@b@ // Add the bytes@b@ dArr[d++] = (byte) (i >> 16);@b@ dArr[d++] = (byte) (i >> 8);@b@ dArr[d++] = (byte) i;@b@@b@ // If line separator, jump over it.@b@ if (sepCnt > 0 && ++cc == 19) {@b@ sIx += 2;@b@ cc = 0;@b@ }@b@ }@b@@b@ if (d < len) {@b@ // Decode last 1-3 bytes (incl '=') into 1-3 bytes@b@ int i = 0;@b@ for (int j = 0; sIx <= eIx - pad; j++)@b@ i |= IA[s.charAt(sIx++)] << (18 - j * 6);@b@@b@ for (int r = 16; d < len; r -= 8)@b@ dArr[d++] = (byte) (i >> r);@b@ }@b@@b@ return dArr;@b@ }@b@}