ArrayAllocator.java

/*
 * ArrayAllocator.java February 2001
 *
 * Copyright (C) 2001, Niall Gallagher <niallg@users.sf.net>
 *
 * 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 org.simpleframework.util.buffer;

import java.io.IOException;

/**
 * The <code>ArrayAllocator</code> object is used to provide a means to allocate
 * buffers using a single byte array. This essentially uses the heap to allocate
 * all buffers. As a result the performance of the resulting buffers is good,
 * however for very large buffers this will use quote allot of the usable heap
 * space. For very large buffers a mapped region of shared memory of a file
 * should be considered.
 * 
 * @author Niall Gallagher
 */
public class ArrayAllocator implements Allocator {

    /**
     * This represents the largest portion of memory that is allowed.
     */
    private int limit;

    /**
     * This represents the default capacity of all allocated buffers.
     */
    private int size;

    /**
     * Constructor for the <code>ArrayAllocator</code> object. This is used to
     * instantiate the allocator with a default buffer size of half a kilobyte.
     * This ensures that it can be used for general purpose byte storage and for
     * minor I/O tasks.
     */
    public ArrayAllocator() {
        this(512);
    }

    /**
     * Constructor for the <code>ArrayAllocator</code> object. This is used to
     * instantiate the allocator with a specified buffer size. This is typically
     * used when a very specific buffer capacity is required, for example a
     * request body with a known length.
     * 
     * @param size
     *            the initial capacity of the allocated buffers
     */
    public ArrayAllocator(int size) {
        this(size, 1048576);
    }

    /**
     * Constructor for the <code>ArrayAllocator</code> object. This is used to
     * instantiate the allocator with a specified buffer size. This is typically
     * used when a very specific buffer capacity is required, for example a
     * request body with a known length.
     * 
     * @param size
     *            the initial capacity of the allocated buffers
     * @param limit
     *            this is the maximum buffer size created by this
     */
    public ArrayAllocator(int size, int limit) {
        this.limit = Math.max(size, limit);
        this.size = size;
    }

    /**
     * This method is used to allocate a default buffer. This will allocate a
     * buffer of predetermined size, allowing it to grow to an upper limit to
     * accommodate extra data. If the buffer requested is larger than the limit
     * an exception is thrown.
     * 
     * @return this returns an allocated buffer with a default size
     */
    @Override
    public Buffer allocate() throws IOException {
        return this.allocate(this.size);
    }

    /**
     * This method is used to allocate a default buffer. This will allocate a
     * buffer of predetermined size, allowing it to grow to an upper limit to
     * accommodate extra data. If the buffer requested is larger than the limit
     * an exception is thrown.
     * 
     * @param size
     *            the initial capacity of the allocated buffer
     * 
     * @return this returns an allocated buffer with a default size
     */
    @Override
    public Buffer allocate(long size) throws IOException {
        int required = (int) size;

        if (size > this.limit)
            throw new BufferException("Specified size %s beyond limit", size);
        return new ArrayBuffer(required, this.limit);
    }

    /**
     * This method is used to close the allocator so that resources that are
     * occupied by the allocator can be freed. This will allow the allocator to
     * be created and closed repeatedly in a single process without holding on
     * to resources such as mapped file buffers or threads.
     */
    @Override
    public void close() throws IOException {
        return;
    }
}