1 /* 2 * Copyright (C) 2011 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 5 * in compliance with the License. You may obtain a copy of the License at 6 * 7 * http://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software distributed under the License 10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 11 * or implied. See the License for the specific language governing permissions and limitations under 12 * the License. 13 */ 14 15 package com.google.common.hash; 16 17 import static com.google.common.base.Preconditions.checkNotNull; 18 19 import com.google.common.annotations.Beta; 20 21 import java.io.FilterOutputStream; 22 import java.io.IOException; 23 import java.io.OutputStream; 24 25 /** 26 * An {@link OutputStream} that maintains a hash of the data written to it. 27 * 28 * @author Nick Piepmeier 29 * @since 16.0 30 */ 31 @Beta 32 public final class HashingOutputStream extends FilterOutputStream { 33 private final Hasher hasher; 34 35 /** 36 * Creates an output stream that hashes using the given {@link HashFunction}, and forwards all 37 * data written to it to the underlying {@link OutputStream}. 38 * 39 * <p>The {@link OutputStream} should not be written to before or after the hand-off. 40 */ 41 // TODO(user): Evaluate whether it makes sense to always piggyback the computation of a 42 // HashCode on an existing OutputStream, compared to creating a separate OutputStream that could 43 // be (optionally) be combined with another if needed (with something like 44 // MultiplexingOutputStream). 45 public HashingOutputStream(HashFunction hashFunction, OutputStream out) { 46 super(checkNotNull(out)); 47 this.hasher = checkNotNull(hashFunction.newHasher()); 48 } 49 50 @Override public void write(int b) throws IOException { 51 hasher.putByte((byte) b); 52 out.write(b); 53 } 54 55 @Override public void write(byte[] bytes, int off, int len) throws IOException { 56 hasher.putBytes(bytes, off, len); 57 out.write(bytes, off, len); 58 } 59 60 /** 61 * Returns the {@link HashCode} based on the data written to this stream. The result is 62 * unspecified if this method is called more than once on the same instance. 63 */ 64 public HashCode hash() { 65 return hasher.hash(); 66 } 67 68 // Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior: 69 // it silently ignores any exception thrown by flush(). Instead, just close the delegate stream. 70 // It should flush itself if necessary. 71 @Override public void close() throws IOException { 72 out.close(); 73 } 74 } 75
