Here you can find the source of encode(byte[] source, int off, int len, byte[] alphabet, boolean doPadding)
| Parameter | Description |
|---|---|
| source | The data to convert |
| off | Offset in array where conversion should begin |
| len | Length of data to convert |
| alphabet | is the encoding alphabet |
| doPadding | is true to pad result with '=' chars if it does not fall on 3 byte boundaries |
public static String encode(byte[] source, int off, int len, byte[] alphabet, boolean doPadding)
//package com.java2s; // Licensed under the Apache License, Version 2.0 (the "License"); public class Main { /** The equals sign (=) as a byte. */ private final static byte EQUALS_SIGN = (byte) '='; /** The new line character (\n) as a byte. */ private final static byte NEW_LINE = (byte) '\n'; /**//from w w w . ja v a 2s . c o m * The 64 valid Base64 values. */ private final static byte[] ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9', (byte) '+', (byte) '/' }; /** * Encodes a byte array into Base64 notation. * Equivalent to calling * {@code encodeBytes(source, 0, source.length)} * * @param source The data to convert * @since 1.4 */ public static String encode(byte[] source) { return encode(source, 0, source.length, ALPHABET, true); } /** * Encodes a byte array into Base64 notation. * * @param source The data to convert * @param off Offset in array where conversion should begin * @param len Length of data to convert * @param alphabet is the encoding alphabet * @param doPadding is {@code true} to pad result with '=' chars * if it does not fall on 3 byte boundaries * @since 1.4 */ public static String encode(byte[] source, int off, int len, byte[] alphabet, boolean doPadding) { byte[] outBuff = encode(source, off, len, alphabet, Integer.MAX_VALUE); int outLen = outBuff.length; // If doPadding is false, set length to truncate '=' // padding characters while (doPadding == false && outLen > 0) { if (outBuff[outLen - 1] != '=') { break; } outLen -= 1; } return new String(outBuff, 0, outLen); } /** * Encodes a byte array into Base64 notation. * * @param source The data to convert * @param off Offset in array where conversion should begin * @param len Length of data to convert * @param alphabet is the encoding alphabet * @param maxLineLength maximum length of one line. * @return the BASE64-encoded byte array */ public static byte[] encode(byte[] source, int off, int len, byte[] alphabet, int maxLineLength) { int lenDiv3 = (len + 2) / 3; // ceil(len / 3) int len43 = lenDiv3 * 4; byte[] outBuff = new byte[len43 // Main 4:3 + (len43 / maxLineLength)]; // New lines int d = 0; int e = 0; int len2 = len - 2; int lineLength = 0; for (; d < len2; d += 3, e += 4) { // The following block of code is the same as // encode3to4( source, d + off, 3, outBuff, e, alphabet ); // but inlined for faster encoding (~20% improvement) int inBuff = ((source[d + off] << 24) >>> 8) | ((source[d + 1 + off] << 24) >>> 16) | ((source[d + 2 + off] << 24) >>> 24); outBuff[e] = alphabet[(inBuff >>> 18)]; outBuff[e + 1] = alphabet[(inBuff >>> 12) & 0x3f]; outBuff[e + 2] = alphabet[(inBuff >>> 6) & 0x3f]; outBuff[e + 3] = alphabet[(inBuff) & 0x3f]; lineLength += 4; if (lineLength == maxLineLength) { outBuff[e + 4] = NEW_LINE; e++; lineLength = 0; } // end if: end of line } // end for: each piece of array if (d < len) { encode3to4(source, d + off, len - d, outBuff, e, alphabet); lineLength += 4; if (lineLength == maxLineLength) { // Add a last newline outBuff[e + 4] = NEW_LINE; e++; } e += 4; } assert (e == outBuff.length); return outBuff; } /** * Encodes up to three bytes of the array <var>source</var> * and writes the resulting four Base64 bytes to <var>destination</var>. * The source and destination arrays can be manipulated * anywhere along their length by specifying * <var>srcOffset</var> and <var>destOffset</var>. * This method does not check to make sure your arrays * are large enough to accommodate <var>srcOffset</var> + 3 for * the <var>source</var> array or <var>destOffset</var> + 4 for * the <var>destination</var> array. * The actual number of significant bytes in your array is * given by <var>numSigBytes</var>. * * @param source the array to convert * @param srcOffset the index where conversion begins * @param numSigBytes the number of significant bytes in your array * @param destination the array to hold the conversion * @param destOffset the index where output will be put * @param alphabet is the encoding alphabet * @return the <var>destination</var> array * @since 1.3 */ private static byte[] encode3to4(byte[] source, int srcOffset, int numSigBytes, byte[] destination, int destOffset, byte[] alphabet) { // 1 2 3 // 01234567890123456789012345678901 Bit position // --------000000001111111122222222 Array position from threeBytes // --------| || || || | Six bit groups to index alphabet // >>18 >>12 >> 6 >> 0 Right shift necessary // 0x3f 0x3f 0x3f Additional AND // Create buffer with zero-padding if there are only one or two // significant bytes passed in the array. // We have to shift left 24 in order to flush out the 1's that appear // when Java treats a value as negative that is cast from a byte to an int. int inBuff = (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0) | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0) | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0); switch (numSigBytes) { case 3: destination[destOffset] = alphabet[(inBuff >>> 18)]; destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f]; destination[destOffset + 3] = alphabet[(inBuff) & 0x3f]; return destination; case 2: destination[destOffset] = alphabet[(inBuff >>> 18)]; destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = alphabet[(inBuff >>> 6) & 0x3f]; destination[destOffset + 3] = EQUALS_SIGN; return destination; case 1: destination[destOffset] = alphabet[(inBuff >>> 18)]; destination[destOffset + 1] = alphabet[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = EQUALS_SIGN; destination[destOffset + 3] = EQUALS_SIGN; return destination; default: return destination; } // end switch } }