Java tutorial
/* * Copyright 2009 Google Inc. * * 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 * * 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 com.google.gwt.user.server; /** * A utility to decode and encode byte arrays as Strings, using only "safe" * characters. */ public class Base64Utils { /** * An array mapping size but values to the characters that will be used to * represent them. Note that this is not identical to the set of characters * used by MIME-Base64. */ private static final char[] base64Chars = new char[] { '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', '$', '_' }; /** * An array mapping legal base 64 characters [a-zA-Z0-9$_] to their associated * 6-bit values. The source indices will be given by 7-bit ASCII characters, * thus the array size needs to be 128 (actually 123 would suffice for the * given set of characters in use). */ private static final byte[] base64Values = new byte[128]; /** * Initialize the base 64 encoder values. */ static { // Invert the mapping (i -> base64Chars[i]) for (int i = 0; i < base64Chars.length; i++) { base64Values[base64Chars[i]] = (byte) i; } } /** * Decode a base64 string into a byte array. * * @param data the encoded data. * @return a byte array. * @see #fromBase64(String) */ public static byte[] fromBase64(String data) { if (data == null) { return null; } int len = data.length(); assert (len % 4) == 0; if (len == 0) { return new byte[0]; } char[] chars = new char[len]; data.getChars(0, len, chars, 0); int olen = 3 * (len / 4); if (chars[len - 2] == '=') { --olen; } if (chars[len - 1] == '=') { --olen; } byte[] bytes = new byte[olen]; int iidx = 0; int oidx = 0; while (iidx < len) { int c0 = base64Values[chars[iidx++] & 0xff]; int c1 = base64Values[chars[iidx++] & 0xff]; int c2 = base64Values[chars[iidx++] & 0xff]; int c3 = base64Values[chars[iidx++] & 0xff]; int c24 = (c0 << 18) | (c1 << 12) | (c2 << 6) | c3; bytes[oidx++] = (byte) (c24 >> 16); if (oidx == olen) { break; } bytes[oidx++] = (byte) (c24 >> 8); if (oidx == olen) { break; } bytes[oidx++] = (byte) c24; } return bytes; } /** * Decode a base64 string into a long value. */ public static long longFromBase64(String value) { int pos = 0; long longVal = base64Values[value.charAt(pos++)]; int len = value.length(); while (pos < len) { longVal <<= 6; longVal |= base64Values[value.charAt(pos++)]; } return longVal; } /** * Converts a byte array into a base 64 encoded string. Null is encoded as * null, and an empty array is encoded as an empty string. Otherwise, the byte * data is read 3 bytes at a time, with bytes off the end of the array padded * with zeros. Each 24-bit chunk is encoded as 4 characters from the sequence * [A-Za-z0-9$_]. If one of the source positions consists entirely of padding * zeros, an '=' character is used instead. * * @param data a byte array, which may be null or empty * @return a String */ public static String toBase64(byte[] data) { if (data == null) { return null; } int len = data.length; if (len == 0) { return ""; } int olen = 4 * ((len + 2) / 3); char[] chars = new char[olen]; int iidx = 0; int oidx = 0; int charsLeft = len; while (charsLeft > 0) { int b0 = data[iidx++] & 0xff; int b1 = (charsLeft > 1) ? data[iidx++] & 0xff : 0; int b2 = (charsLeft > 2) ? data[iidx++] & 0xff : 0; int b24 = (b0 << 16) | (b1 << 8) | b2; int c0 = (b24 >> 18) & 0x3f; int c1 = (b24 >> 12) & 0x3f; int c2 = (b24 >> 6) & 0x3f; int c3 = b24 & 0x3f; chars[oidx++] = base64Chars[c0]; chars[oidx++] = base64Chars[c1]; chars[oidx++] = (charsLeft > 1) ? base64Chars[c2] : '='; chars[oidx++] = (charsLeft > 2) ? base64Chars[c3] : '='; charsLeft -= 3; } return new String(chars); } /** * Return a string containing a base-64 encoded version of the given long * value. Leading groups of all zero bits are omitted. */ public static String toBase64(long value) { // Convert to ints early to avoid need for long ops int low = (int) (value & 0xffffffff); int high = (int) (value >> 32); StringBuilder sb = new StringBuilder(); boolean haveNonZero = base64Append(sb, (high >> 28) & 0xf, false); haveNonZero = base64Append(sb, (high >> 22) & 0x3f, haveNonZero); haveNonZero = base64Append(sb, (high >> 16) & 0x3f, haveNonZero); haveNonZero = base64Append(sb, (high >> 10) & 0x3f, haveNonZero); haveNonZero = base64Append(sb, (high >> 4) & 0x3f, haveNonZero); int v = ((high & 0xf) << 2) | ((low >> 30) & 0x3); haveNonZero = base64Append(sb, v, haveNonZero); haveNonZero = base64Append(sb, (low >> 24) & 0x3f, haveNonZero); haveNonZero = base64Append(sb, (low >> 18) & 0x3f, haveNonZero); haveNonZero = base64Append(sb, (low >> 12) & 0x3f, haveNonZero); base64Append(sb, (low >> 6) & 0x3f, haveNonZero); base64Append(sb, low & 0x3f, true); return sb.toString(); } private static boolean base64Append(StringBuilder sb, int digit, boolean haveNonZero) { if (digit > 0) { haveNonZero = true; } if (haveNonZero) { sb.append(base64Chars[digit]); } return haveNonZero; } }