How to get number of bytes?

How do I obtain the number of bytes before allocating the byte size of the array 'handsize' as shown below as the incoming ByteArray data are sent in 3 different sizes. Thanks.

Buf开发者_开发问答feredInputStream bais = new  

BufferedInputStream(requestSocket.getInputStream()); 

DataInputStream datainput = new DataInputStream(bais); 

//need to read the number of bytes here before proceeding.

byte[] handsize = new byte[bytesize];  

datainput.readFully(handsize); 

You could use a ByteArrayOutputStream, then you wouldn't have to worry about it.

ByteArrayOutputStream out = new ByteArrayOutputStream();
//write data to output stream
byte[] bytes = out.toByteArray();

There's no way to know how many bytes of data are yet to be received on a socket--knowing this would be tantamount to clairvoyance. If you're using your own protocol for client/server communication, you could send the number of bytes of data as an integer, before sending the actual bytes themselves. Then the receiving side would know how many bytes to expect.

As has been pointed out, the problem as stated is impossible. But why do you need to know? Why not store the data in a variable size structure, like an ArrayList, as you read it? Or maybe even process it as you read?