Converting byte array to int array in Java, via ByteBuffer to IntBuffer, without truncating

Question

There are other questions posted here on this topic, most of which involve ByteBuffer and asIntBuffer. However, I have not seen any explaination on how to keep the value from truncating when converting to an IntBuffer.

Example:

byte[] plainTextBytes = "Hello World".getBytes();

// Truncates the limit from 11 to 2
IntBuffer intBuffer = ByteBuffer.wrap( plainTextBytes ).asIntBuffer();

// Results in java.lang.UnsupportedOperationException
int[] plainTextInt = intBuffer.array();

I have an RC4 encryption algorithm which takes a plaintext argument of type int[]. Hence, I need to convert the plaintext into int[]. The problem with ByteBuffer and the use of asIntBuffer is the plaintext is being truncated because the limit is independent (goes from 11 to 2, in my example).

Either I'm doing something wrong or ByteBuffer is not the way to go here.

Any help would be appreciated. Thank you.

The problem is an int size in java is 4bytes. Your bytebuffer contains 11bytes. Which is a complete 2 int(8bytes). Do you absolutely need to use byte buffer? other solutions might work for you like using the bytes array directly as ints. — user5156016
– user5156016, Commented Oct 26, 2015 at 17:36
No, not at all. I don't need to use byte buffer. But most of the answers on StackOverFlow pointed to byte buffer. I'm open to any solution that converts byte array to int array. Thank you. — user3621633
– user3621633, Commented Oct 26, 2015 at 17:38

user5156016 · Accepted Answer · 2015-10-26 17:39:40Z

2

Hi you can try this if you do not need to use IntBuffer.

byte[] plainTextBytes = "Hello World".getBytes();

int[] ints = new int[plainTextBytes.length];

for(int i = 0; i < ints.length; i++){
    ints[i] = plainTextBytes[i];
}

You basically convert bytes directly into ints.

answered Oct 26, 2015 at 17:39

user5156016

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2 Comments

user3621633 Over a year ago

Thank you very much! This should work. Not sure what the point of byte buffer is if it's just going to truncate when converting to int buffer from it. I have no idea why your answer was downvoted. I just tried it and it seems to work. The only thing I would change is inside the for loop, I think it should be ints[i] = plainTextBytes[i] & 0xFF, in order to keep the range from 0-255. Thanks again.

frifle Over a year ago

This is the way to go +1

frifle · Accepted Answer · 2015-10-27 09:11:01Z

Using Buffer#array is not suitable for your needs. The documentation says

Returns the byte array that backs this buffer (optional operation).

Throws:
ReadOnlyBufferException - If this buffer is backed by an array but is read-only
UnsupportedOperationException - If this buffer is not backed by accessible array

You are using two Buffers in your code. The first one is a ByteBuffer which wraps an array. Thus this Buffer is backed by an array and a call to #array() is valid. The second one you create via #asIntBuffer(). This Buffer is only a view of the first buffer which is not backed by an array. So you see the UnsupportedOperationException when calling array().

You want to encrypt a byte[], but your algorithm works on a int[]. Then Jawad answer is your way to go.

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