byte[] to String conversion with proper truncation in Java

Question

I have a byte array of size 200 that has data received with socket.receive(). Let's say the packet data is "hello".

int size = 200;
DatagramPacket packet = new DatagramPacket(new byte[size], size);
socket.receive(packet);
byte[] byte1 = packet.getData();

I tried to convert the byte array into string, and the string length is 200 even though it prints out only 'hello' string.

String result = new String(byte1); // .toString();
System.out.println(result.length()); --> 200
System.out.println(result); ---> hello

How can I truncate the String to contain only "hello" when converting it from byte[]?

ADDED

Based on malchow's answer, this solved my issue:

int packetLength = packet.getLength();
byte[] byte1 = packet.getData();
String result = new String(byte1);
return result.substring(0, packetLength);

If the extra bites are all empty/whitespace, trim() should do it. — Thomas
– Thomas, Commented Apr 23, 2013 at 2:31
Something's fishy here. How do you, as a client, know when you've received the entire string? That is - what way do you have of knowing that you've gotten all of the character data? — Matt Ball
– Matt Ball, Commented Apr 23, 2013 at 2:32
This is a part of unit test code, so I know exactly the string I sent. — prosseek
– prosseek, Commented Apr 23, 2013 at 2:34
@Thomas: It works. Please make an answer so that I accept it. — prosseek
– prosseek, Commented Apr 23, 2013 at 2:36

rmalchow · Accepted Answer · 2013-04-23 02:40:00Z

1

maybe you should try to check the length of the data received AFTER receiving it:

http://docs.oracle.com/javase/1.5.0/docs/api/java/net/DatagramPacket.html#getLength%28%29

this should be 4 (after the call to socket.receive())

answered Apr 23, 2013 at 2:40

rmalchow

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rmalchow Over a year ago

the "setLength()" method is for sending, not for receiving.

Thomas · Accepted Answer · 2013-04-23 02:37:29Z

0

If the extra bites are all empty/whitespace, trim() should do it.

answered Apr 23, 2013 at 2:37

Thomas

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rmalchow Over a year ago

this is actually incorrect if the message in the datagram is SUPPOSED to contain leading and/or trailing whitespace. please consider my answer below (with a link to the documentation)

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