com.google.common.hash.HashingOutputStream Maven / Gradle / Ivy
/*
* Copyright (C) 2011 The Guava Authors
*
* 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.
*/
package com.google.common.hash;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;
/**
* An {@link OutputStream} that maintains a hash of the data written to it.
*
* @author Nick Piepmeier
* @since 16.0
*/
@Beta
@ElementTypesAreNonnullByDefault
public final class HashingOutputStream extends FilterOutputStream {
private final Hasher hasher;
/**
* Creates an output stream that hashes using the given {@link HashFunction}, and forwards all
* data written to it to the underlying {@link OutputStream}.
*
* The {@link OutputStream} should not be written to before or after the hand-off.
*/
// TODO(user): Evaluate whether it makes sense to always piggyback the computation of a
// HashCode on an existing OutputStream, compared to creating a separate OutputStream that could
// be (optionally) be combined with another if needed (with something like
// MultiplexingOutputStream).
public HashingOutputStream(HashFunction hashFunction, OutputStream out) {
super(checkNotNull(out));
this.hasher = checkNotNull(hashFunction.newHasher());
}
@Override
public void write(int b) throws IOException {
hasher.putByte((byte) b);
out.write(b);
}
@Override
public void write(byte[] bytes, int off, int len) throws IOException {
hasher.putBytes(bytes, off, len);
out.write(bytes, off, len);
}
/**
* Returns the {@link HashCode} based on the data written to this stream. The result is
* unspecified if this method is called more than once on the same instance.
*/
public HashCode hash() {
return hasher.hash();
}
// Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
// it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
// It should flush itself if necessary.
@Override
public void close() throws IOException {
out.close();
}
}