CODEWITHSUNDEEP
javanio
Roshan
Roshan

Reputation: 290

How to convert a ByteBuffer to long[] in Java

Can someone please let me know how to convert a a ByteBuffer into a long[]?

I had a long[] to begin with, which I converted to a ByteBuffer using the following piece of code:

byte[] convertToByteArray(long[] data) {
    ByteBuffer byteBuffer = ByteBuffer.allocate(data.length * 8);;
    LongBuffer longBuffer = byteBuffer.asLongBuffer();
    longBuffer.put(data);
    return byteBuffer.array();
}

I would now like to do the reverse, and write a few tests comparing the various arrays before and after conversion.

I tried the following, but it fails with an NPE on JDK 1.6.0_26:

long[] convertToLongArray(byte[] bArray) {
    ByteBuffer byteBuffer = ByteBuffer.wrap(bArray);
    LongBuffer longBuffer = byteBuffer.asLongBuffer();
    return longBuffer.array();
}

Regards, Roshan

Upvotes: 2

Views: 4139

Answers (1)

Claudiu
Claudiu

Reputation: 1489

on my side it throws 

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.nio.LongBuffer.array(LongBuffer.java:994)
    at test.convertToLongArray(test.java:11)
    at test.main(test.java:15)

It does that because the instance returned by byteBuffer.asLongBuffer() call is a ByteBufferAsLongBufferL or ByteBufferAsLongBufferB class (depending on the indianess). Both of these 2 classes are sub-classes of LongBuffer and inside the constructor call super constructor is called without the long array parameter.

As @Kayaman mentioned, these are only views for the byte array from ByteBuffer.

Below is the super constructor called from the ByteBufferAsLongBufferL constructor. Notice the null parameter.

LongBuffer(int mark, int pos, int lim, int cap) { // package-private
    this(mark, pos, lim, cap, null, 0);
}

The best option is to do this:

long[] convertToLongArray(byte[] bArray) {
    ByteBuffer byteBuffer = ByteBuffer.wrap(bArray);
    LongBuffer longBuffer = byteBuffer.asLongBuffer();
    long l[] = new long[longBuffer.capacity()];
    longBuffer.get(l);
    return l;
}

Upvotes: 3

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