Java tutorial
package org.bouncycastle.util.encoders; import java.io.IOException; import java.io.OutputStream; /** * A streaming Base64 encoder. */ public class Base64Encoder implements Encoder { protected final byte[] encodingTable = { (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) '/' }; protected byte padding = (byte) '='; /* * set up the decoding table. */ protected final byte[] decodingTable = new byte[128]; protected void initialiseDecodingTable() { for (int i = 0; i < decodingTable.length; i++) { decodingTable[i] = (byte) 0xff; } for (int i = 0; i < encodingTable.length; i++) { decodingTable[encodingTable[i]] = (byte) i; } } public Base64Encoder() { initialiseDecodingTable(); } /** * encode the input data producing a base 64 output stream. * * @return the number of bytes produced. */ public int encode(byte[] data, int off, int length, OutputStream out) throws IOException { int modulus = length % 3; int dataLength = (length - modulus); int a1, a2, a3; for (int i = off; i < off + dataLength; i += 3) { a1 = data[i] & 0xff; a2 = data[i + 1] & 0xff; a3 = data[i + 2] & 0xff; out.write(encodingTable[(a1 >>> 2) & 0x3f]); out.write(encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f]); out.write(encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f]); out.write(encodingTable[a3 & 0x3f]); } /* * process the tail end. */ int b1, b2, b3; int d1, d2; switch (modulus) { case 0: /* nothing left to do */ break; case 1: d1 = data[off + dataLength] & 0xff; b1 = (d1 >>> 2) & 0x3f; b2 = (d1 << 4) & 0x3f; out.write(encodingTable[b1]); out.write(encodingTable[b2]); out.write(padding); out.write(padding); break; case 2: d1 = data[off + dataLength] & 0xff; d2 = data[off + dataLength + 1] & 0xff; b1 = (d1 >>> 2) & 0x3f; b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f; b3 = (d2 << 2) & 0x3f; out.write(encodingTable[b1]); out.write(encodingTable[b2]); out.write(encodingTable[b3]); out.write(padding); break; } return (dataLength / 3) * 4 + ((modulus == 0) ? 0 : 4); } private boolean ignore(char c) { return (c == '\n' || c == '\r' || c == '\t' || c == ' '); } /** * decode the base 64 encoded byte data writing it to the given output stream, * whitespace characters will be ignored. * * @return the number of bytes produced. */ public int decode(byte[] data, int off, int length, OutputStream out) throws IOException { byte b1, b2, b3, b4; int outLen = 0; int end = off + length; while (end > off) { if (!ignore((char) data[end - 1])) { break; } end--; } // empty data! if (end == 0) { return 0; } int i = 0; int finish = end; while (finish > off && i != 4) { if (!ignore((char) data[finish - 1])) { i++; } finish--; } i = nextI(data, off, finish); while (i < finish) { b1 = decodingTable[data[i++]]; i = nextI(data, i, finish); b2 = decodingTable[data[i++]]; i = nextI(data, i, finish); b3 = decodingTable[data[i++]]; i = nextI(data, i, finish); b4 = decodingTable[data[i++]]; if ((b1 | b2 | b3 | b4) < 0) { throw new IOException("invalid characters encountered in base64 data"); } out.write((b1 << 2) | (b2 >> 4)); out.write((b2 << 4) | (b3 >> 2)); out.write((b3 << 6) | b4); outLen += 3; i = nextI(data, i, finish); } int e0 = nextI(data, i, end); int e1 = nextI(data, e0 + 1, end); int e2 = nextI(data, e1 + 1, end); int e3 = nextI(data, e2 + 1, end); outLen += decodeLastBlock(out, (char) data[e0], (char) data[e1], (char) data[e2], (char) data[e3]); return outLen; } private int nextI(byte[] data, int i, int finish) { while ((i < finish) && ignore((char) data[i])) { i++; } return i; } /** * decode the base 64 encoded String data writing it to the given output stream, * whitespace characters will be ignored. * * @return the number of bytes produced. */ public int decode(String data, OutputStream out) throws IOException { byte b1, b2, b3, b4; int length = 0; int end = data.length(); while (end > 0) { if (!ignore(data.charAt(end - 1))) { break; } end--; } // empty data! if (end == 0) { return 0; } int i = 0; int finish = end; while (finish > 0 && i != 4) { if (!ignore(data.charAt(finish - 1))) { i++; } finish--; } i = nextI(data, 0, finish); while (i < finish) { b1 = decodingTable[data.charAt(i++)]; i = nextI(data, i, finish); b2 = decodingTable[data.charAt(i++)]; i = nextI(data, i, finish); b3 = decodingTable[data.charAt(i++)]; i = nextI(data, i, finish); b4 = decodingTable[data.charAt(i++)]; if ((b1 | b2 | b3 | b4) < 0) { throw new IOException("invalid characters encountered in base64 data"); } out.write((b1 << 2) | (b2 >> 4)); out.write((b2 << 4) | (b3 >> 2)); out.write((b3 << 6) | b4); length += 3; i = nextI(data, i, finish); } int e0 = nextI(data, i, end); int e1 = nextI(data, e0 + 1, end); int e2 = nextI(data, e1 + 1, end); int e3 = nextI(data, e2 + 1, end); length += decodeLastBlock(out, data.charAt(e0), data.charAt(e1), data.charAt(e2), data.charAt(e3)); return length; } private int decodeLastBlock(OutputStream out, char c1, char c2, char c3, char c4) throws IOException { byte b1, b2, b3, b4; if (c3 == padding) { if (c4 != padding) { throw new IOException("invalid characters encountered at end of base64 data"); } b1 = decodingTable[c1]; b2 = decodingTable[c2]; if ((b1 | b2) < 0) { throw new IOException("invalid characters encountered at end of base64 data"); } out.write((b1 << 2) | (b2 >> 4)); return 1; } else if (c4 == padding) { b1 = decodingTable[c1]; b2 = decodingTable[c2]; b3 = decodingTable[c3]; if ((b1 | b2 | b3) < 0) { throw new IOException("invalid characters encountered at end of base64 data"); } out.write((b1 << 2) | (b2 >> 4)); out.write((b2 << 4) | (b3 >> 2)); return 2; } else { b1 = decodingTable[c1]; b2 = decodingTable[c2]; b3 = decodingTable[c3]; b4 = decodingTable[c4]; if ((b1 | b2 | b3 | b4) < 0) { throw new IOException("invalid characters encountered at end of base64 data"); } out.write((b1 << 2) | (b2 >> 4)); out.write((b2 << 4) | (b3 >> 2)); out.write((b3 << 6) | b4); return 3; } } private int nextI(String data, int i, int finish) { while ((i < finish) && ignore(data.charAt(i))) { i++; } return i; } }