Java tutorial
/* * Copyright 2007 Werner Guttmann * * 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. */ import java.io.IOException; import java.io.OutputStream; import java.io.ByteArrayOutputStream; /** * Hex encoder/decoder implementation (borrowed from BouncyCastle=. * * @author Johan Lindquist * @since 1.1.1 * @version $Revision$ */ public final class HexDecoder { /** * Identifies the data type supported by this decoder. */ public static final String DATA_TYPE = "hexBinary"; /** * Initial size of the decoding table. */ private static final int DECODING_TABLE_SIZE = 128; /** * Encoding table. */ protected static final byte[] ENCODING_TABLE = { (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9', (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F' }; /** * Decoding table. */ protected static final byte[] DECODING_TABLE = new byte[DECODING_TABLE_SIZE]; /** * Initialize the decoding table. */ protected static void initialiseDecodingTable() { for (int i = 0; i < ENCODING_TABLE.length; i++) { DECODING_TABLE[ENCODING_TABLE[i]] = (byte) i; } // deal with lower case letters as well DECODING_TABLE['a'] = DECODING_TABLE['A']; DECODING_TABLE['b'] = DECODING_TABLE['B']; DECODING_TABLE['c'] = DECODING_TABLE['C']; DECODING_TABLE['d'] = DECODING_TABLE['D']; DECODING_TABLE['e'] = DECODING_TABLE['E']; DECODING_TABLE['f'] = DECODING_TABLE['F']; } static { initialiseDecodingTable(); } /** * Creates an instance of this class. */ private HexDecoder() { // Nothing to do ... } /** * Encodes the input data producing a Hex output stream. * @param data The input data to be HEX encoded * @param off Initiak offset * @param length Initial length of the input data array * @param out The {@link OutputStream} instance holding the encoded input data. * @return the number of bytes produced. * @throws IOException If encoding fails. */ public static int encode(final byte[] data, final int off, final int length, final OutputStream out) throws IOException { for (int i = off; i < (off + length); i++) { int v = data[i] & 0xff; out.write(ENCODING_TABLE[(v >>> 4)]); out.write(ENCODING_TABLE[v & 0xf]); } return length * 2; } /** * Indicates whether a given character should be ignored during en-/decoding. * @param c The character at question. * @return True if the given character should be ignored. */ private static boolean ignore(final char c) { return (c == '\n' || c == '\r' || c == '\t' || c == ' '); } /** * Decodes the Hex encoded byte data writing it to the given output stream, * whitespace characters will be ignored. * @param data The data to be encoded * @param off Initial offset. * @param length Initial length * @param out The {@link OutputStream} instance * @return the number of bytes produced. * @throws IOException If encoding failed. */ public static int decode(final byte[] data, final int off, final int length, final OutputStream out) throws IOException { byte b1, b2; int outLen = 0; int end = off + length; while (end > off) { if (!ignore((char) data[end - 1])) { break; } end--; } int i = off; while (i < end) { while (i < end && ignore((char) data[i])) { i++; } b1 = DECODING_TABLE[data[i++]]; while (i < end && ignore((char) data[i])) { i++; } b2 = DECODING_TABLE[data[i++]]; out.write((b1 << 4) | b2); outLen++; } return outLen; } /** * Decodes the Hex encoded String data writing it to the given output stream, * whitespace characters will be ignored. * * @param data The data to be encoded * @param out The {@link OutputStream} instance * @return the number of bytes produced. * @throws IOException If encoding failed. */ public static int decode(final String data, final OutputStream out) throws IOException { byte b1, b2; int length = 0; int end = data.length(); while (end > 0) { if (!ignore(data.charAt(end - 1))) { break; } end--; } int i = 0; while (i < end) { while (i < end && ignore(data.charAt(i))) { i++; } b1 = DECODING_TABLE[data.charAt(i++)]; while (i < end && ignore(data.charAt(i))) { i++; } b2 = DECODING_TABLE[data.charAt(i++)]; out.write((b1 << 4) | b2); length++; } return length; } /** * Encodes the input data producing a Hex output stream. * @param data Input data to encode. * @return the number of bytes produced. */ public static String encode(final byte[] data) { try { final ByteArrayOutputStream out = new ByteArrayOutputStream(); encode(data, 0, data.length, out); out.close(); return new String(out.toByteArray()); } catch (IOException e) { e.printStackTrace(); throw new RuntimeException(e.getMessage(), e); } } /** * Decodes the HEX input data producing a output stream. * @param data Input data to be decoded. * @return A byte array representing the decoded input data. */ public static byte[] decode(final String data) { try { final ByteArrayOutputStream out = new ByteArrayOutputStream(); decode(data, out); out.close(); return out.toByteArray(); } catch (IOException e) { e.printStackTrace(); throw new RuntimeException(e.getMessage(), e); } } }