Java tutorial
// // NOTE: The following source code is heavily derived from the // iHarder.net public domain Base64 library. See the original at // http://iharder.sourceforge.net/current/java/base64/ // package org.eclipse.jgit.util; import static java.nio.charset.StandardCharsets.UTF_8; import java.text.MessageFormat; import java.util.Arrays; import org.eclipse.jgit.internal.JGitText; /** * Encodes and decodes to and from Base64 notation. * <p> * I am placing this code in the Public Domain. Do with it as you will. This * software comes with no guarantees or warranties but with plenty of * well-wishing instead! Please visit * <a href="http://iharder.net/base64">http://iharder.net/base64</a> * periodically to check for updates or to contribute improvements. * </p> * * @author Robert Harder * @author rob@iharder.net */ public class Base64 { /** The equals sign (=) as a byte. */ private final static byte EQUALS_SIGN = (byte) '='; /** Indicates equals sign in encoding. */ private final static byte EQUALS_SIGN_DEC = -1; /** Indicates white space in encoding. */ private final static byte WHITE_SPACE_DEC = -2; /** Indicates an invalid byte during decoding. */ private final static byte INVALID_DEC = -3; /** The 64 valid Base64 values. */ private final static byte[] ENC; /** * Translates a Base64 value to either its 6-bit reconstruction value or a * negative number indicating some other meaning. The table is only 7 bits * wide, as the 8th bit is discarded during decoding. */ private final static byte[] DEC; static { ENC = ("ABCDEFGHIJKLMNOPQRSTUVWXYZ" // //$NON-NLS-1$ + "abcdefghijklmnopqrstuvwxyz" // //$NON-NLS-1$ + "0123456789" // //$NON-NLS-1$ + "+/" // //$NON-NLS-1$ ).getBytes(UTF_8); DEC = new byte[128]; Arrays.fill(DEC, INVALID_DEC); for (int i = 0; i < 64; i++) DEC[ENC[i]] = (byte) i; DEC[EQUALS_SIGN] = EQUALS_SIGN_DEC; DEC['\t'] = WHITE_SPACE_DEC; DEC['\n'] = WHITE_SPACE_DEC; DEC['\r'] = WHITE_SPACE_DEC; DEC[' '] = WHITE_SPACE_DEC; } /** Defeats instantiation. */ private Base64() { // Suppress empty block warning. } /** * 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 */ private static void encode3to4(byte[] source, int srcOffset, int numSigBytes, byte[] destination, int destOffset) { // 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. int inBuff = 0; switch (numSigBytes) { case 3: inBuff |= (source[srcOffset + 2] << 24) >>> 24; //$FALL-THROUGH$ case 2: inBuff |= (source[srcOffset + 1] << 24) >>> 16; //$FALL-THROUGH$ case 1: inBuff |= (source[srcOffset] << 24) >>> 8; } switch (numSigBytes) { case 3: destination[destOffset] = ENC[(inBuff >>> 18)]; destination[destOffset + 1] = ENC[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = ENC[(inBuff >>> 6) & 0x3f]; destination[destOffset + 3] = ENC[(inBuff) & 0x3f]; break; case 2: destination[destOffset] = ENC[(inBuff >>> 18)]; destination[destOffset + 1] = ENC[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = ENC[(inBuff >>> 6) & 0x3f]; destination[destOffset + 3] = EQUALS_SIGN; break; case 1: destination[destOffset] = ENC[(inBuff >>> 18)]; destination[destOffset + 1] = ENC[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = EQUALS_SIGN; destination[destOffset + 3] = EQUALS_SIGN; break; } } /** * Encodes a byte array into Base64 notation. * * @param source * The data to convert * @return encoded base64 representation of source. */ public static String encodeBytes(byte[] source) { return encodeBytes(source, 0, source.length); } /** * 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 * @return encoded base64 representation of source. */ public static String encodeBytes(byte[] source, int off, int len) { final int len43 = len * 4 / 3; byte[] outBuff = new byte[len43 + ((len % 3) > 0 ? 4 : 0)]; int d = 0; int e = 0; int len2 = len - 2; for (; d < len2; d += 3, e += 4) encode3to4(source, d + off, 3, outBuff, e); if (d < len) { encode3to4(source, d + off, len - d, outBuff, e); e += 4; } return new String(outBuff, 0, e, UTF_8); } /** * Decodes four bytes from array <var>source</var> and writes the resulting * bytes (up to three of them) 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> + 4 for the <var>source</var> array or * <var>destOffset</var> + 3 for the <var>destination</var> array. This * method returns the actual number of bytes that were converted from the * Base64 encoding. * * @param source * the array to convert * @param srcOffset * the index where conversion begins * @param destination * the array to hold the conversion * @param destOffset * the index where output will be put * @return the number of decoded bytes converted */ private static int decode4to3(byte[] source, int srcOffset, byte[] destination, int destOffset) { // Example: Dk== if (source[srcOffset + 2] == EQUALS_SIGN) { int outBuff = ((DEC[source[srcOffset]] & 0xFF) << 18) | ((DEC[source[srcOffset + 1]] & 0xFF) << 12); destination[destOffset] = (byte) (outBuff >>> 16); return 1; } // Example: DkL= else if (source[srcOffset + 3] == EQUALS_SIGN) { int outBuff = ((DEC[source[srcOffset]] & 0xFF) << 18) | ((DEC[source[srcOffset + 1]] & 0xFF) << 12) | ((DEC[source[srcOffset + 2]] & 0xFF) << 6); destination[destOffset] = (byte) (outBuff >>> 16); destination[destOffset + 1] = (byte) (outBuff >>> 8); return 2; } // Example: DkLE else { int outBuff = ((DEC[source[srcOffset]] & 0xFF) << 18) | ((DEC[source[srcOffset + 1]] & 0xFF) << 12) | ((DEC[source[srcOffset + 2]] & 0xFF) << 6) | ((DEC[source[srcOffset + 3]] & 0xFF)); destination[destOffset] = (byte) (outBuff >> 16); destination[destOffset + 1] = (byte) (outBuff >> 8); destination[destOffset + 2] = (byte) (outBuff); return 3; } } /** * Low-level decoding ASCII characters from a byte array. * * @param source * The Base64 encoded data * @param off * The offset of where to begin decoding * @param len * The length of characters to decode * @return decoded data * @throws java.lang.IllegalArgumentException * the input is not a valid Base64 sequence. */ public static byte[] decode(byte[] source, int off, int len) { byte[] outBuff = new byte[len * 3 / 4]; // Upper limit on size of output int outBuffPosn = 0; byte[] b4 = new byte[4]; int b4Posn = 0; for (int i = off; i < off + len; i++) { byte sbiCrop = (byte) (source[i] & 0x7f); byte sbiDecode = DEC[sbiCrop]; if (EQUALS_SIGN_DEC <= sbiDecode) { b4[b4Posn++] = sbiCrop; if (b4Posn > 3) { outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn); b4Posn = 0; // If that was the equals sign, break out of 'for' loop if (sbiCrop == EQUALS_SIGN) break; } } else if (sbiDecode != WHITE_SPACE_DEC) throw new IllegalArgumentException(MessageFormat.format(JGitText.get().badBase64InputCharacterAt, Integer.valueOf(i), Integer.valueOf(source[i] & 0xff))); } if (outBuff.length == outBuffPosn) return outBuff; byte[] out = new byte[outBuffPosn]; System.arraycopy(outBuff, 0, out, 0, outBuffPosn); return out; } /** * Decodes data from Base64 notation. * * @param s * the string to decode * @return the decoded data */ public static byte[] decode(String s) { byte[] bytes = s.getBytes(UTF_8); return decode(bytes, 0, bytes.length); } }