Receive messages from socket python server

Question

I tried to read message on socket with bufferreader

My client:

Socket socket = new Socket("10.0.0.4", 12345);

BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

System.out.println(in.readLine());

My python server:

(client, (address, _)) = server.accept()  # Accept to new clients (Accept to new command from the phone)
client.send("Hello from server")

But when I send a message from the server to the client, the code gets stack in the last line System.out.println(in.readLine()); like he is waiting for something.

And whan I turn off the server, I get an error.

How can I read the input from my server with Java?

`readLine` is waiting for a new line character. Is a newline being sent? — James, Dec 20 '20 at 21:17

aran · Accepted Answer · 2020-12-20T22:13:41.913

2

As @James comment states, seems like you are waiting for a carriage return or line feed (complete line) that is not being sent by the server.

That leads to your code being waiting forever until \n, \r or \r\n are received.

readLine()

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

So your in.readline() never considers the line to be terminated, and keeps hopefully waiting for it to end. In order to avoid this, instead of sending:

   client.send("Hello from server")

Send

   client.send("Hello from server\n")

Or even better, check if that Python library has something similar to a sendLine() method.

In order to loop receiving server's messages, something like this could work:

while (socket.isConnected()) 
{
  String inputLine;
  while ((inputLine = in.readLine()) != null)
      System.out.println(inputLine);
}

edited Dec 20 '20 at 22:13

answered Dec 20 '20 at 21:16

aran

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It still does not print anything and seems to be waiting for something – Ziv Sion Dec 20 '20 at 21:18
1

the maybe the socket is not connected at all? updating – aran Dec 20 '20 at 21:19
1

this would avoid any wait if the socket is not connected. Are you sure the server is sending anything? – aran Dec 20 '20 at 21:21
Yes I'm sure, because, when I tried to read the messages with ```DataInputStream``` and I tried to read as int, I got 84 (It means that I got the message from the server) – Ziv Sion Dec 20 '20 at 21:22
But I don't know what is going to work for me, because ```DataInputStream``` can't sow me string – Ziv Sion Dec 20 '20 at 21:24
show*********** – Ziv Sion Dec 20 '20 at 21:24
Check out my edit in 20 sec – Ziv Sion Dec 20 '20 at 21:25
1

Send this instead: client.send("Hello from server \n") – aran Dec 20 '20 at 21:28
```java: incompatible types: int cannot be converted to java.lang.String``` I got an error – Ziv Sion Dec 20 '20 at 21:28
I can't check if int is null – Ziv Sion Dec 20 '20 at 21:28
Thanks!!!!!!!!!!!!!!!!!! You have no idea how many nights I sat on it – Ziv Sion Dec 20 '20 at 21:31
1

now you can go to sleep in peace mate : ) – aran Dec 20 '20 at 21:31
1

Thank you! There are no words in my mouth to thank you – Ziv Sion Dec 20 '20 at 21:32
1000 € in my bank account would be enough : ) Just kidding, good luck in life mate – aran Dec 20 '20 at 21:35
1

Thank you mate. Have a good day – Ziv Sion Dec 20 '20 at 21:37

Receive messages from socket python server

1 Answers1