Sending int through socket in Java

Question

What is the best possible way to send an int through a socket in Java? Right now I'm looking at

sockout.write((byte)( length >> 24 ));
sockout.write((byte)( (length << 8) >> 24 ));
sockout.write((byte)( (length << 16) >> 24 ));
sockout.write((byte)( (length << 24) >> 24 ));

and then trying to rebuild the int from bytes on the other side, but it doesn't seem to work. Any ideas?

Thanks.

Solution 1

Wrap your OutputStream with a DataOutputStream and then just use the writeInt() method.

Something else which may be useful is that on the other end you can wrap our InputStream in a DataInputStream and use readInt() to read an int back out.

Both classes also contain a number of other useful methods for reading and writing other raw types.

Solution 2

There are other type of streams you can use, which can directly send integers. You can use DataOutputStream. Observe,

DataOutputStream out;
try {
    //create write stream to send information
    out=new DataOutputStream(sock.getOutputStream());
} catch (IOException e) { 
    //Bail out
}

out.writeInt(5);

Comments

[Denis Tulskiy]

Only if there's also java of the other end.

[jtahlborn]

@DenisTulskiy - the other end could be any language. the DataOutputStream writes almost entirely language agnostic output (except the utf8 strings).

[arkon]

@jtahlborn Why are utf8 strings an exception? Isn't it all ultimately just bytes anyway?

[Adam Batkin]

@b1naryatr0phy Well, writeUTF() uses a format that isn't universal (as opposed to sending an integer, which, other than endianness is universal). That's because it sends the length (as a short, which is worrying) followed by the UTF-8 bytes. There's nothing wrong or proprietary about that format, so you just have to make sure that the other end is expecting that (as opposed to, say, sending the length as an int or sending a fixed-size string with no length marker)

[arkon]

@AdamBatkin I understand now, thanks for clarifying that for me.

[leonbloy]

However, DataOutputStream closes wrapped stream when it's closed, which can be a problem.