com.google.common.hash.HashingOutputStream.java Source code

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Here is the source code for com.google.common.hash.HashingOutputStream.java

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/*
 * 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;

import javax.annotation.CheckReturnValue;

/**
 * An {@link OutputStream} that maintains a hash of the data written to it.
 *
 * @author Nick Piepmeier
 * @since 16.0
 */
@Beta
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}.
     *
     * <p>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.
     */
    @CheckReturnValue
    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();
    }
}