Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You 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 * * http://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 org.apache.solr.common.util; /** * Static methods for translating Base64 encoded strings to byte arrays * and vice-versa. */ public class Base64 { /** * This array is a lookup table that translates 6-bit positive integer * index values into their "Base64 Alphabet" equivalents as specified * in Table 1 of RFC 2045. */ private static final char intToBase64[] = { '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', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/' }; /** * This array is a lookup table that translates unicode characters * drawn from the "Base64 Alphabet" (as specified in Table 1 of RFC 2045) * into their 6-bit positive integer equivalents. Characters that * are not in the Base64 alphabet but fall within the bounds of the * array are translated to -1. */ private static final byte base64ToInt[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 }; public static String byteArrayToBase64(byte[] a) { return byteArrayToBase64(a, 0, a.length); } public static String byteArrayToBase64(byte[] a, int offset, int len) { int aLen = len; int numFullGroups = aLen / 3; int numBytesInPartialGroup = aLen - 3 * numFullGroups; int resultLen = 4 * ((aLen + 2) / 3); StringBuilder result = new StringBuilder(resultLen); char[] intToAlpha = intToBase64; // Translate all full groups from byte array elements to Base64 int inCursor = offset; for (int i = 0; i < numFullGroups; i++) { int byte0 = a[inCursor++] & 0xff; int byte1 = a[inCursor++] & 0xff; int byte2 = a[inCursor++] & 0xff; result.append(intToAlpha[byte0 >> 2]); result.append(intToAlpha[(byte0 << 4) & 0x3f | (byte1 >> 4)]); result.append(intToAlpha[(byte1 << 2) & 0x3f | (byte2 >> 6)]); result.append(intToAlpha[byte2 & 0x3f]); } // Translate partial group if present if (numBytesInPartialGroup != 0) { int byte0 = a[inCursor++] & 0xff; result.append(intToAlpha[byte0 >> 2]); if (numBytesInPartialGroup == 1) { result.append(intToAlpha[(byte0 << 4) & 0x3f]); result.append("=="); } else { // assert numBytesInPartialGroup == 2; int byte1 = a[inCursor++] & 0xff; result.append(intToAlpha[(byte0 << 4) & 0x3f | (byte1 >> 4)]); result.append(intToAlpha[(byte1 << 2) & 0x3f]); result.append('='); } } return result.toString(); } public static byte[] base64ToByteArray(String s) { byte[] alphaToInt = base64ToInt; int sLen = s.length(); int numGroups = sLen / 4; if (4 * numGroups != sLen) throw new IllegalArgumentException("String length must be a multiple of four."); int missingBytesInLastGroup = 0; int numFullGroups = numGroups; if (sLen != 0) { if (s.charAt(sLen - 1) == '=') { missingBytesInLastGroup++; numFullGroups--; } if (s.charAt(sLen - 2) == '=') missingBytesInLastGroup++; } byte[] result = new byte[3 * numGroups - missingBytesInLastGroup]; // Translate all full groups from base64 to byte array elements int inCursor = 0, outCursor = 0; for (int i = 0; i < numFullGroups; i++) { int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt); result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4)); result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2)); result[outCursor++] = (byte) ((ch2 << 6) | ch3); } // Translate partial group, if present if (missingBytesInLastGroup != 0) { int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt); result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4)); if (missingBytesInLastGroup == 1) { int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt); result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2)); } } // assert inCursor == s.length()-missingBytesInLastGroup; // assert outCursor == result.length; return result; } /** * Translates the specified character, which is assumed to be in the * "Base 64 Alphabet" into its equivalent 6-bit positive integer. * * @throw IllegalArgumentException or ArrayOutOfBoundsException if * c is not in the Base64 Alphabet. */ private static int base64toInt(char c, byte[] alphaToInt) { int result = alphaToInt[c]; if (result < 0) throw new IllegalArgumentException("Illegal character " + c); return result; } }