How to Wrap a ByteBuffer for Use as an InputStream in Java?

Question

How can I convert a ByteBuffer to an InputStream in Java to read data from it?

import java.io.InputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.ByteChannel;
import java.nio.channels.ReadableByteChannel;

public class ByteBufferInputStream extends InputStream {
    private final ReadableByteChannel channel;
    private final ByteBuffer buffer;

    public ByteBufferInputStream(ByteBuffer buffer) {
        this.buffer = buffer;
        this.channel = Channels.newChannel(new ByteBufferInputStream(buffer));
    }

    @Override
    public int read() throws IOException {
        if (!buffer.hasRemaining()) {
            return -1; // EOF
        }
        return buffer.get() & 0xFF; // Return the byte in unsigned format
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (!buffer.hasRemaining()) {
            return -1; // EOF
        }
        int bytesRead = Math.min(len, buffer.remaining());
        buffer.get(b, off, bytesRead);
        return bytesRead;
    }
}

Answer

In Java, to convert a ByteBuffer into an InputStream, you can create a custom class that extends InputStream and uses the ByteBuffer’s methods to read bytes. Below, I will provide a comprehensive implementation and explanation.

import java.io.InputStream;
import java.nio.ByteBuffer;

public class ByteBufferInputStream extends InputStream {
    private final ByteBuffer buffer;

    public ByteBufferInputStream(ByteBuffer buffer) {
        this.buffer = buffer;
    }

    @Override
    public int read() throws IOException {
        if (!buffer.hasRemaining()) {
            return -1; // EOF
        }
        return buffer.get() & 0xFF; // Return byte as unsigned
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (len == 0) {
            return 0;
        }
        if (!buffer.hasRemaining()) {
            return -1; // EOF
        }
        int bytesRead = Math.min(len, buffer.remaining());
        buffer.get(b, off, bytesRead);
        return bytesRead;
    }
}

Causes

You want to read data from a ByteBuffer using a method designed for InputStream.
Handling data streams in Java often requires the use of InputStream interfaces.

Solutions

Implement a custom InputStream class that mirrors the behavior of a ByteBuffer.
Use Java's new channels for improved data handling.

Common Mistakes

Mistake: Failing to check if the ByteBuffer has remaining bytes before reading.

Solution: Always verify using buffer.hasRemaining() before calling get() to prevent unwanted exceptions.

Mistake: Not considering end-of-file (EOF) conditions gracefully.

Solution: Handle EOF by returning -1 when no more bytes are available.

Helpers

ByteBuffer
InputStream
Java
ByteBuffer to InputStream
converting ByteBuffer to InputStream
Java IO