PoolingByteArrayOutputStream.java

/*
 * Copyright (C) 2014 Neal
 *
 * 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 neal.http.utils;

/**
 * Created by Neal on 2014/10/28.
 */

import java.io.ByteArrayOutputStream;
import java.io.IOException;

/**
 * A variation of {@link java.io.ByteArrayOutputStream} that uses a pool of byte[] buffers instead
 * of always allocating them fresh, saving on heap churn.
 */
public class PoolingByteArrayOutputStream extends ByteArrayOutputStream {
    /**
     * If the {@link #PoolingByteArrayOutputStream(neal.http.utils.ByteArrayPool)} constructor is called, this is
     * the default size to which the underlying byte array is initialized.
     */
    private static final int DEFAULT_SIZE = 256;

    private final ByteArrayPool mPool;

    /**
     * Constructs a new PoolingByteArrayOutputStream with a default size. If more bytes are written
     * to this instance, the underlying byte array will expand.
     */
    public PoolingByteArrayOutputStream(ByteArrayPool pool) {
        this(pool, DEFAULT_SIZE);
    }

    /**
     * Constructs a new {@code ByteArrayOutputStream} with a default size of {@code size} bytes. If
     * more than {@code size} bytes are written to this instance, the underlying byte array will
     * expand.
     *
     * @param size initial size for the underlying byte array. The value will be pinned to a default
     *        minimum size.
     */
    public PoolingByteArrayOutputStream(ByteArrayPool pool, int size) {
        mPool = pool;
        buf = mPool.getBuf(Math.max(size, DEFAULT_SIZE));
    }

    @Override
    public void close() throws IOException {
        mPool.returnBuf(buf);
        buf = null;
        super.close();
    }

    @Override
    public void finalize() {
        mPool.returnBuf(buf);
    }

    /**
     * Ensures there is enough space in the buffer for the given number of additional bytes.
     */
    private void expand(int i) {
        /* Can the buffer handle @i more bytes, if not expand it */
        if (count + i <= buf.length) {
            return;
        }
        byte[] newbuf = mPool.getBuf((count + i) * 2);
        System.arraycopy(buf, 0, newbuf, 0, count);
        mPool.returnBuf(buf);
        buf = newbuf;
    }

    @Override
    public synchronized void write(byte[] buffer, int offset, int len) {
        expand(len);
        super.write(buffer, offset, len);
    }

    @Override
    public synchronized void write(int oneByte) {
        expand(1);
        super.write(oneByte);
    }
}