Sending JSON from Python to Java

Question

I'm trying to send JSON from a Python client to a Java server

The JSON data type is bytes (in Python) and when I deserialize it (in Python) and print it, it looks perfect. The server works fine when a Java client connects and when I deserialize the JSON and print it in Java it looks exactly the same as in Python and the actual JSON files. The JSON all looks good, but the data isn't accepted by the Java server.

data = open(file_path, 'r').read() # reading JSON object as string
serialized_data = pickle.dumps(data)

s.send(serialized_data)

When I send a JSON file the Java server acknowledges the connection but the JSON data for whatever reason isn't accepted.

Java Client

String sentence = new String(readFile());

if(!sentence.equals("fileNotFound")) {
    ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
    oos.writeObject(sentence);
}

Java Server

ObjectInputStream inFromClient = new ObjectInputStream(socket.getInputStream());
String clientString = null;
try {
    clientString = (String) inFromClient.readObject();
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}
inFromClient.close();

Please include the lines from the Java & Python clients which actually do the send. It could be a `content-type` issue. — root, Feb 02 '20 at 06:52
if I print the Python send `print(s.send(value))` I get a number back. The server should accept whatever, it's coded to accept JSON, XML or text — Harley, Feb 02 '20 at 07:31

Stephen C · Accepted Answer · 2020-02-02T07:47:23.693

2

You appear to be doing this:

Read JSON from file as a String
Pickle the string
Send the pickle to Java.

That won't work. A pickle is a Python-specific serialization format. Java doesn't understand it.

The data you are reading from the file is already serialized .... as JSON.

Solution: send the string containing the JSON without pickling it.

On the other hand, if the Java server expects to receive something that has been serialized using ObjectOutputStream, then you have a bigger problem. The Java Object Serialization protocol is Java specific. Python doesn't support it. But if you are actually sending JSON to the server you should need to do that. Change the server to accept JSON, and get rid of the ObjectInputStream / ObjectOutputStream code on both sides.

On the third hand, if you can't get rid of the ObjectInputStream / ObjectOutputStream stuff, then maybe you need to modify the server side to either provide a separate API for python to call, or get the server to check the request's "content-type" header and handle either form of data serialization (JSON and Object Serialization protocol)

edited Feb 02 '20 at 07:47

answered Feb 02 '20 at 07:33

Stephen C

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The socket send says TypeError: a bytes-like object is required, not 'str' – Harley Feb 02 '20 at 07:40
`s.send(value.encode())` The data is sent as a string but still no joy. – Harley Feb 02 '20 at 07:47
So convert the string to a bytes-like object; e.g. https://stackoverflow.com/questions/11624190/python-convert-string-to-byte-array – Stephen C Feb 02 '20 at 07:48
Yea. I suspect that the lack of joy is explained by the stuff with Object Serialization protocol. Did you see that part of my answer? A python client can't do that ... – Stephen C Feb 02 '20 at 07:49
Yeah, I think we were typing at the same time. – Harley Feb 02 '20 at 07:50
Sending as a string, the server gets some data but the data gets messed up. Maybe the accepting JSON might be better, I'll keep playing. – Harley Feb 02 '20 at 08:26
Yeah, sending from Python as a String worked. Took a bit of playing with the server code. But all good. – Harley Feb 02 '20 at 09:37

Sending JSON from Python to Java

1 Answers1