How to Implement a Dynamic Growing ByteBuffer in Java?

Question

How can I implement a ByteBuffer in Java that automatically expands its capacity when full?

import java.nio.ByteBuffer;

public class DynamicByteBuffer {
    private ByteBuffer buffer;

    public DynamicByteBuffer(int initialCapacity) {
        buffer = ByteBuffer.allocate(initialCapacity);
    }

    public void put(byte[] data) {
        if (buffer.remaining() < data.length) {
            growBuffer(data.length);
        }
        buffer.put(data);
    }

    private void growBuffer(int additionalCapacity) {
        ByteBuffer newBuffer = ByteBuffer.allocate(buffer.capacity() + additionalCapacity);
        buffer.flip(); // Prepare the current buffer for reading.
        newBuffer.put(buffer);
        buffer = newBuffer;
    }

    public byte[] getBuffer() {
        return buffer.array();
    }
}

Answer

Implementing a dynamic ByteBuffer in Java requires creating a custom class that leverages the existing ByteBuffer functionality while allowing for repeated allocation of additional capacity as needed. This helps avoid frequent allocations and bulk data moves while providing the flexibility to handle unknown data sizes during runtimes.

import java.nio.ByteBuffer;

public class DynamicByteBuffer {
    private ByteBuffer buffer;

    public DynamicByteBuffer(int initialCapacity) {
        buffer = ByteBuffer.allocate(initialCapacity);
    }

    public void put(byte[] data) {
        if (buffer.remaining() < data.length) {
            growBuffer(data.length);
        }
        buffer.put(data);
    }

    private void growBuffer(int additionalCapacity) {
        ByteBuffer newBuffer = ByteBuffer.allocate(buffer.capacity() + additionalCapacity);
        buffer.flip(); // Prepare the current buffer for reading.
        newBuffer.put(buffer);
        buffer = newBuffer;
    }

    public byte[] getBuffer() {
        return buffer.array();
    }
}

Causes

Unpredicted data input sizes prevent pre-allocating sufficient buffer capacity.
Wasting resources from frequent allocations and copying data between buffers.

Solutions

Use a wrapper class to manage a standard ByteBuffer with capacity expansion.
Implement logic to check the remaining capacity before each data input and allocate more space if necessary.
Use ByteBuffer.flip() to prepare for reading and ByteBuffer.put() for writing data after resizing.

Common Mistakes

Mistake: Failing to check remaining buffer capacity before putting data.

Solution: Always check remaining capacity and expand the buffer if necessary.

Mistake: Not flipping the buffer before transferring data.

Solution: Use buffer.flip() to prepare it for reading before transferring to a new buffer.

Helpers

Java ByteBuffer
Dynamic ByteBuffer
ByteBuffer implementation Java
Java NIO ByteBuffer