Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you 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 org.apache.hadoop.io; import java.io.IOException; import java.io.DataInput; import java.io.DataOutput; import java.io.InputStream; import java.util.Arrays; import java.security.*; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; /** A Writable for MD5 hash values. */ @InterfaceAudience.Public @InterfaceStability.Stable public class MD5Hash implements WritableComparable<MD5Hash> { public static final int MD5_LEN = 16; private static final ThreadLocal<MessageDigest> DIGESTER_FACTORY = new ThreadLocal<MessageDigest>() { @Override protected MessageDigest initialValue() { try { return MessageDigest.getInstance("MD5"); } catch (NoSuchAlgorithmException e) { throw new RuntimeException(e); } } }; private byte[] digest; /** Constructs an MD5Hash. */ public MD5Hash() { this.digest = new byte[MD5_LEN]; } /** Constructs an MD5Hash from a hex string. */ public MD5Hash(String hex) { setDigest(hex); } /** Constructs an MD5Hash with a specified value. */ public MD5Hash(byte[] digest) { if (digest.length != MD5_LEN) throw new IllegalArgumentException("Wrong length: " + digest.length); this.digest = digest; } // javadoc from Writable @Override public void readFields(DataInput in) throws IOException { in.readFully(digest); } /** Constructs, reads and returns an instance. */ public static MD5Hash read(DataInput in) throws IOException { MD5Hash result = new MD5Hash(); result.readFields(in); return result; } // javadoc from Writable @Override public void write(DataOutput out) throws IOException { out.write(digest); } /** Copy the contents of another instance into this instance. */ public void set(MD5Hash that) { System.arraycopy(that.digest, 0, this.digest, 0, MD5_LEN); } /** Returns the digest bytes. */ public byte[] getDigest() { return digest; } /** Construct a hash value for a byte array. */ public static MD5Hash digest(byte[] data) { return digest(data, 0, data.length); } /** * Create a thread local MD5 digester */ public static MessageDigest getDigester() { MessageDigest digester = DIGESTER_FACTORY.get(); digester.reset(); return digester; } /** Construct a hash value for the content from the InputStream. */ public static MD5Hash digest(InputStream in) throws IOException { final byte[] buffer = new byte[4 * 1024]; final MessageDigest digester = getDigester(); for (int n; (n = in.read(buffer)) != -1;) { digester.update(buffer, 0, n); } return new MD5Hash(digester.digest()); } /** Construct a hash value for a byte array. */ public static MD5Hash digest(byte[] data, int start, int len) { byte[] digest; MessageDigest digester = getDigester(); digester.update(data, start, len); digest = digester.digest(); return new MD5Hash(digest); } /** Construct a hash value for an array of byte array. */ public static MD5Hash digest(byte[][] dataArr, int start, int len) { byte[] digest; MessageDigest digester = getDigester(); for (byte[] data : dataArr) { digester.update(data, start, len); } digest = digester.digest(); return new MD5Hash(digest); } /** Construct a hash value for a String. */ public static MD5Hash digest(String string) { return digest(UTF8.getBytes(string)); } /** Construct a hash value for a String. */ public static MD5Hash digest(UTF8 utf8) { return digest(utf8.getBytes(), 0, utf8.getLength()); } /** Construct a half-sized version of this MD5. Fits in a long **/ public long halfDigest() { long value = 0; for (int i = 0; i < 8; i++) value |= ((digest[i] & 0xffL) << (8 * (7 - i))); return value; } /** * Return a 32-bit digest of the MD5. * @return the first 4 bytes of the md5 */ public int quarterDigest() { int value = 0; for (int i = 0; i < 4; i++) value |= ((digest[i] & 0xff) << (8 * (3 - i))); return value; } /** Returns true iff <code>o</code> is an MD5Hash whose digest contains the * same values. */ @Override public boolean equals(Object o) { if (!(o instanceof MD5Hash)) return false; MD5Hash other = (MD5Hash) o; return Arrays.equals(this.digest, other.digest); } /** Returns a hash code value for this object. * Only uses the first 4 bytes, since md5s are evenly distributed. */ @Override public int hashCode() { return quarterDigest(); } /** Compares this object with the specified object for order.*/ @Override public int compareTo(MD5Hash that) { return WritableComparator.compareBytes(this.digest, 0, MD5_LEN, that.digest, 0, MD5_LEN); } /** A WritableComparator optimized for MD5Hash keys. */ public static class Comparator extends WritableComparator { public Comparator() { super(MD5Hash.class); } @Override public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) { return compareBytes(b1, s1, MD5_LEN, b2, s2, MD5_LEN); } } static { // register this comparator WritableComparator.define(MD5Hash.class, new Comparator()); } private static final char[] HEX_DIGITS = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' }; /** Returns a string representation of this object. */ @Override public String toString() { StringBuilder buf = new StringBuilder(MD5_LEN * 2); for (int i = 0; i < MD5_LEN; i++) { int b = digest[i]; buf.append(HEX_DIGITS[(b >> 4) & 0xf]); buf.append(HEX_DIGITS[b & 0xf]); } return buf.toString(); } /** Sets the digest value from a hex string. */ public void setDigest(String hex) { if (hex.length() != MD5_LEN * 2) throw new IllegalArgumentException("Wrong length: " + hex.length()); byte[] digest = new byte[MD5_LEN]; for (int i = 0; i < MD5_LEN; i++) { int j = i << 1; digest[i] = (byte) (charToNibble(hex.charAt(j)) << 4 | charToNibble(hex.charAt(j + 1))); } this.digest = digest; } private static final int charToNibble(char c) { if (c >= '0' && c <= '9') { return c - '0'; } else if (c >= 'a' && c <= 'f') { return 0xa + (c - 'a'); } else if (c >= 'A' && c <= 'F') { return 0xA + (c - 'A'); } else { throw new RuntimeException("Not a hex character: " + c); } } }