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How to receive only actual data from a socket

i am sending 20 bytes of data from my udpserver to a client in java. At the client side i am receiving like this
byte[] buf = new byte[25];
final DatagramPacket recv = new DatagramPacket(buf,25);
String data = new String(recv.getData());
when i print data it is printing additional things. How can i only get my actual data. Please suggest.

You are sending 20 bytes, but you are allocating a receive buffer that can receive up to 25 bytes. The received datagram can be smaller, but you need to take the actual received length into account when constructing the String, eg:
String data = new String(recv.getData(), 0, recv.getLength());

UDP Packet sent not being read by server correctly

I'm sending two packets from a client to server. The issue I'm having is the data being read on the server makes both strings the same length with regards to the longest string sent. For example:
if string 1 was : 1234
and string 2 was: abcdefghi
the server would read
1234efghi
abcdefghi
It should just display
1234
abcdefghi
My code is:
byte[] toSendUser = new byte[1024];
byte[] toSendPass = new byte[1024];
String name = "1234";
String password = "abcdefghi";
toSendUser = name.getBytes();
toSendPass = password.getBytes();
DatagramPacket packSend = new DatagramPacket (toSendUser, toSendUser.length, ipConn, 9876);
connection.send(packSend);
DatagramPacket packSendtwo = new DatagramPacket (toSendPass, toSendPass.length, ipConn, 9876);
connection.send(packSendtwo);
Could it be a server issue or is my code wrong in my client?

DatagramPackets in Java keep shrinking to the size of the smallest one received so far. You have to either create a new one per receive(), or at least reset the length every time before the next receive().

java client python server sending udp data

I am trying to create a client in java which sends data to a python server using UDP,but i am having trouble sending data. Every example which i have seen or read so far is something like this:
byte[] buf = new byte[256];
InetAddress address = InetAddress.getLocalHost();
DatagramPacket packet = new DatagramPacket(buf, buf.length, ip,port);
System.out.println("Sending...");
socket.send(packet);
What i can't figure out is how can i send my data which can be of type int or char or string or even an array?? I mean how do I change these to byte,put it in buf and send them.
Can it then be simply be decoded on python client like this:
data,addr = self.sock.recvfrom(1024)
data = data.decode()
EDIT:
I have figured out how to convert strings to byte, by doing:
buf = "hello".getBytes();
But still no clue on integers and arrays..

You can create "protocole" JSON-based like this:
{"items":[ {"type":'string", "value":"test"}, {"type":"int", "value":3}]}
and use https://code.google.com/p/json-simple/wiki/EncodingExamples#Example_1-1_-_Encode_a_JSON_object to encode it.

getOffset() of a packet returns 0 on the receiver's end

I have a lengthy text file that I am trying to transport across UDP on localhost so naturally I have to break up the byte buffer to send the file in packets.
The problem I'm having is this:
On the server side, I send a packet of data with the offset into the byte buffer set to say 500:
byte[] buf = text.getBytes();
InetAddress address = InetAddress.getByName("localhost");
DatagramPacket packet = new DatagramPacket(buf, 500, BYTES_PER_PACKET, address, udp_port_num);
System.out.println("Offset at server: " + packet.getOffset());
udpSocket.send(packet);
The print statement returns the expected answer of 500.
But then on the client side:
byte[] buf = new byte[BYTES_PER_PACKET];
DatagramPacket packet = new DatagramPacket(buf, BYTES_PER_PACKET);
udpSocket.receive(packet);
String received = new String(packet.getData());
System.out.println(received);
System.out.println("Offset: " + packet.getOffset());
It prints the correct text from the offset of the file in received, but packet.getOffset() always returns 0. Why isn't it returning the same 500 from the server and/or how can I get it to return the same 500 from the server?
Thanks in advance

The meaning of all this is:
At the sender you created a DatagramPacket using bytes 500..BYTES_PER_PACKET-500 of the source array.
You sent the packet. It went over the wire as a UDP datagram. It arrived as a UDP datagram.
At the receiver, you constructed a new byte array, and constructed a new DatagramPacket around it, specifying offset = 0, or no offset parameter. You received into the DatagramPacket. Java put the UDP datagram into the byte array in the DatagramPacket, starting at the offset you specified: zero.
Note that the sender's DatagramPacket did not itself go over the wire, nor the sender's byte array either.

Failed to convert data from UDP packet into the initial data which is sent using Java

I'm writing a UDP Client to transfer a file to a UDP server. First I try to measure the length of the file, devided by the buffer length to be sent in UDP packet, to get the number of packets required to be sent. I send this number to the server first to acknowledge it. But on the server side, the transform from byte array of the receiving packet into the initial number just failed. Can anyone help me out of this? Here is my code on the client side:
DatagramSocket socket=new DatagramSocket();
File f = new File(filename);
long fileSize = f.length();
byte[] buffer = new byte[16384];
long packetNumber = (fileSize/(buffer.length))+1;
DatagramPacket sendPacket=new DatagramPacket(buffer,buffer.length,addr,srvPort);
String str=Long.toString(packetNumber);
buffer = str.getBytes();
socket.send(sendPacket);
And here is the code on the server side:
DatagramSocket socket=new DatagramSocket(port);
byte[] buffer=new byte[16384];
DatagramPacket receivePacket=new DatagramPacket(buffer, buffer.length);
while(true)
{
socket.receive(receivePacket);
if (receivePacket.getData().toString().trim()!=null)
{
String str=receivePacket.getData().toString();
System.out.println(str);
long pcount=Long.parseLong(str);
System.out.println(pcount+" packets to be received.");
break;
}
}
But on the server side the variable pcount can always not be resolved, and when I try to print out the str, it writes out some "[B#60991f" or sth, weird.

This code doesn't make any sense.
Most networks won't let you send a datagram over 534 bytes reliably.
At present you are sending 16384 bytes of zero value, because you aren't putting anything into the buffer: instead you are creating a new buffer after creating the DatagramPacket. So you aren't sending anything yet.
And you aren't receiving anything yet either. The result of String.trim() cannot be null. You must reset the byte array in a DatagramPacket before every receive(), because it shrinks to the size of the actual received packet, so unless you reset it it keeps getting smaller and smaller. The result of toString() on a byte array does not include its contents, so parsing it is futile.
You need to study several basic Java programming concepts: too many to answer here.

You're receiving a byte array, using toString() won't give you anything.
You should reconstruct the String from the bytes array using new String