Java ByteBuffer Append appendOrRealloc(ByteBuffer dest, ByteBuffer toAppend)

Description

Appends the contents of toAppend to dest if there is capacity, or does the equivalent of C's "realloc" by allocating a larger buffer and copying both dest and toAppend into that new buffer.

License

Open Source License

Parameter

Parameter	Description
dest	The buffer into which to write or to reallocate if necessary.
toAppend	The data to write into dest.

Return

dest or a new, larger buffer containing both dest and toAppend.

Declaration

static ByteBuffer appendOrRealloc(ByteBuffer dest, ByteBuffer toAppend)

Method Source Code

//package com.java2s;
/*************************************************************************
*                                                                        *
*  This file is part of the 20n/act project.                             *
*  20n/act enables DNA prediction for synthetic biology/bioengineering.  *
*  Copyright (C) 2017 20n Labs, Inc.                                     *
*                                                                        *
*  Please direct all queries to act@20n.com.                             *
*                                                                        *
*  This program is free software: you can redistribute it and/or modify  *
*  it under the terms of the GNU General Public License as published by  *
*  the Free Software Foundation, either version 3 of the License, or     *
*  (at your option) any later version.                                   *
*                                                                        *
*  This program is distributed in the hope that it will be useful,       *
*  but WITHOUT ANY WARRANTY; without even the implied warranty of        *
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
*  GNU General Public License for more details.                          *
*                                                                        *
*  You should have received a copy of the GNU General Public License     *
*  along with this program.  If not, see <http://www.gnu.org/licenses/>. *
*                                                                        *
*************************************************************************/

import java.nio.ByteBuffer;

public class Main {
    /**/*  w w  w .  j ava  2 s  .c om*/
     * Appends the contents of toAppend to dest if there is capacity, or does the equivalent of C's "realloc" by
     * allocating a larger buffer and copying both dest and toAppend into that new buffer.
     *
     * Always call this function as:
     * <pre>
     * {@code
     *   dest = appendOrRealloc(dest, toAppend)
     * }
     * </pre>
     * as we can't actually resize or reallocate dest once it's been allocated.
     *
     * @param dest The buffer into which to write or to reallocate if necessary.
     * @param toAppend The data to write into dest.
     * @return dest or a new, larger buffer containing both dest and toAppend.
     */
    static ByteBuffer appendOrRealloc(ByteBuffer dest, ByteBuffer toAppend) {
        /* Before reading this function, review this excellent explanation of the behaviors of ByteBuffers:
         * http://mindprod.com/jgloss/bytebuffer.html */

        // Assume toAppend is pre-flipped to avoid a double flip, which would be Very Bad.
        if (dest.capacity() - dest.position() < toAppend.limit()) {
            // Whoops, we have to reallocate!

            ByteBuffer newDest = ByteBuffer.allocate(dest.capacity() << 1); // TODO: make sure these are page-divisible sizes.
            dest.flip(); // Switch dest to reading mode.
            newDest.put(dest); // Write all of dest into the new buffer.
            dest = newDest;
        }
        dest.put(toAppend);
        return dest;
    }
}