Java client python server socket programming

Question

I have a client program in java that sends a message "Hello" to python server.

Java code

    import java.io.*;  
    import java.net.*; 
    public class MyClient {
    public static void main(String[] args) {  

    try{      
    Socket soc=new Socket("localhost",2004);  
    DataOutputStream dout=new DataOutputStream(soc.getOutputStream());  
    dout.writeUTF("Hello");
    dout.flush();
    dout.close();  
    soc.close();
    }catch(Exception e){
        e.printStackTrace();}  
    }

Python server code

    import socket               # Import socket module

    soc = socket.socket()         # Create a socket object
    host = "localhost" # Get local machine name
    port = 2004                # Reserve a port for your service.
    soc.bind((host, port))       # Bind to the port
    soc.listen(5)                 # Now wait for client connection.
    while True:
    conn, addr = soc.accept()     # Establish connection with client.
    print ("Got connection from",addr)
    msg = conn.recv(1024)
    print (msg)
    if ( msg == "Hello Server" ):
    print("Hii everyone")
    else:
    print("Go away")

the problem is that java client is able to send a Hello message to the python server but in python side else statement always executes with output " Go away".python version 2.7

Output:

('Got connection from', ('127.0.0.1', 25214))
Hello
Go away

Python does not understand Java's writeUTF() format. Only Java's writeUTF() understands it. Use writeBytes(). — user207421
– user207421, Commented Mar 2, 2019 at 8:38

Adi · Accepted Answer · 2014-08-26 12:24:20Z

4

you are getting 'Hello' from client.

if ( msg == "Hello" ):
    print("Hii everyone")
else:
    print("Go away")

answered Aug 26, 2014 at 12:24

Adi

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Comments

Ngô Thanh Phi · Accepted Answer · 2019-03-02 04:31:34Z

1

because the string you get on the server side has 2 hidden characters at the beginning, so you must remove these 2 characters before comparing it.

if ( msg[2:] == "Hello" ):

edited Mar 2, 2019 at 4:31

answered Mar 2, 2019 at 4:25

Ngô Thanh Phi

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2 Comments

thakee nathees Over a year ago

it worked for the code if ( msg[2:] == b"Hello" ) but what are the hidden characters?

Ngô Thanh Phi Over a year ago

I don't know :D

Erick · Accepted Answer · 2016-07-13 15:27:43Z

0

In the Java code you have written

dout.writeUTF("Hello");

But the Python server expects "Hello Server" to print "Hii Everyone".

Change Java Client code to

dout.writeUTF("Hello Server");

answered Jul 13, 2016 at 15:27

Erick

496 bronze badges

Comments

L Tyrone · Accepted Answer · 2024-07-18 04:12:27Z

When you're transmitting data by using Java on the socket, it is transmitted on a Data Stream, when it is received it remains in the data stream or byte data:

_test/Pyserver.py
Got connection from ('127.0.0.1', 53518)
b'\x00\x0cHello Server'
Go away

The \x00\x0c are special characters included by UTF8 format by Java. As @user10854863 mentioned, if you use dout.writeBytes instead of dout.writeUTF, the output will change to:

Got connection from ('127.0.0.1', 53519)
b'Hello Server'
Go away

In order to get the passing value, you need to instruct python to decode the UTF formatting from input msg, to see its toString Value:

if (  msg.decode('utf-8') == "Hello Server" ):
        print("Hii everyone")

This in turn throws the output as:

_test/Pyserver.py
Got connection from ('127.0.0.1', 53622)
b'Hello Server'
Hii everyone

(Assuming you already knew strings "Hello" and "Hello Server" were a mismatch).

Kannan Ks · Accepted Answer · 2016-11-28 11:50:37Z

-1

Just Use proper syntax. Since you are sending "Hello", "Go away" will be your output.

if ( msg == "Hello Server" ):
    print("Hii everyone")
else:
    print("Go away")

answered Nov 28, 2016 at 11:50

Kannan Ks

1

1 Comment

user207421 Over a year ago

This is not a syntax issue,

Employee · Accepted Answer · 2019-01-01 19:45:28Z

-1

The problem is that you have to specify the decryption UTF-8 in the Python server and then you should use dout.writeBytes("Hello Server") in the Java client.

edited Jan 1, 2019 at 19:45

Employee

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answered Jan 1, 2019 at 16:44

user10854863

1

1 Comment

user207421 Over a year ago

UTF-8 is not an encryption.

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