Java ByteBuffer to String

Question

There is simpler approach to decode a ByteBuffer into a String without any problems, mentioned by Andy Thomas.

String s = StandardCharsets.UTF_8.decode(byteBuffer).toString();

EDIT (2018): The edited sibling answer by @xinyongCheng is a simpler approach, and should be the accepted answer.

Your approach would be reasonable if you knew the bytes are in the platform's default charset. In your example, this is true because k.getBytes() returns the bytes in the platform's default charset.

More frequently, you'll want to specify the encoding. However, there's a simpler way to do that than the question you linked. The String API provides methods that converts between a String and a byte[] array in a particular encoding. These methods suggest using CharsetEncoder/CharsetDecoder "when more control over the decoding [encoding] process is required."

To get the bytes from a String in a particular encoding, you can use a sibling getBytes() method:

byte[] bytes = k.getBytes( StandardCharsets.UTF_8 );

To put bytes with a particular encoding into a String, you can use a different String constructor:

String v = new String( bytes, StandardCharsets.UTF_8 );

Note that ByteBuffer.array() is an optional operation. If you've constructed your ByteBuffer with an array, you can use that array directly. Otherwise, if you want to be safe, use ByteBuffer.get(byte[] dst, int offset, int length) to get bytes from the buffer into a byte array.

Try this:

new String(bytebuffer.array(), "ASCII");

NB. you can't correctly convert a byte array to a String without knowing its encoding.

I hope this helps

Just wanted to point out, it's not safe to assume ByteBuffer.array() will always work.

byte[] bytes;
if(buffer.hasArray()) {
    bytes = buffer.array();
} else {
    bytes = new byte[buffer.remaining()];
    buffer.get(bytes);
}
String v = new String(bytes, charset);

Usually buffer.hasArray() will always be true or false depending on your use case. In practice, unless you really want it to work under any circumstances, it's safe to optimize away the branch you don't need. But the rest of the answers may not work with a ByteBuffer that's been created through ByteBuffer.allocateDirect().

The answers referring to simply calling array() are not quite correct: when the buffer has been partially consumed, or is referring to a part of an array (you can ByteBuffer.wrap an array at a given offset, not necessarily from the beginning), we have to account for that in our calculations. This is the general solution that works for buffers in all cases (does not cover encoding):

if (myByteBuffer.hasArray()) {
    return new String(myByteBuffer.array(),
        myByteBuffer.arrayOffset() + myByteBuffer.position(),
        myByteBuffer.remaining());
} else {
    final byte[] b = new byte[myByteBuffer.remaining()];
    myByteBuffer.duplicate().get(b);
    return new String(b);
}

For the concerns related to encoding, see Andy Thomas' answer.