How to transmit data from Nodejs program to Java program?

Question

Inside the Java class is the following:

Process process = Runtime.getRuntime().exec("node /home/master/code/nodejs/searchLi.js");
process.waitFor();
BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
StringBuilder builder = new StringBuilder();
String line = null;
while ( (line = reader.readLine()) != null) {
    builder.append(line);
    builder.append(System.getProperty("line.separator"));
}
String result = builder.toString();
System.out.println(result);

Inside the nodejs searchLi is the following:

const Stream = require('stream');
const readableStream = new Stream.Readable();
readableStream.push('ping!');
readableStream.push('pong!');
console.log("success");
return "success";

As you can see I tried to implement streams but failed. How to transmit a String from the nodejs file to the Java file?

Joseph Sible-Reinstate Monica · Accepted Answer · 2021-06-01 23:37:00Z

1

Your Java code is fine, but your node.js code isn't using streams properly. Either just stop using a stream of your own and just use process.stdout.write instead, or fix your streams to point there, like this:

const Stream = require('stream');
const readableStream = new Stream.Readable();
readableStream.push('ping!');
readableStream.push('pong!');
readableStream.push(null);
readableStream.pipe(process.stdout);
console.log("success");
return "success";

answered Jun 1, 2021 at 23:37

Joseph Sible-Reinstate Monica

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1 Comment

propre_poli Over a year ago

This is exactly what I was looking for! Thank you!

Dharman · Accepted Answer · 2021-06-01 22:28:33Z

0

You can setup a http server, although for something this small (a string) I suggest using the fs npm library to create a file and have the java program read from it.

I'm not experienced in java but I assume that there is a file reading library.

edited Jun 1, 2021 at 22:28

Dharman♦

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answered Jun 1, 2021 at 22:23

Polygon

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4 Comments

propre_poli Over a year ago

Thank you for your answer! I was just wondering if it was possible to use the return value directly as you would with 2 files of the same language? Are the streams a viable option in your opinion?

Joseph Sible-Reinstate Monica Over a year ago

Spawning an HTTP server to just to communicate between a parent and child process is quite frankly one of the most overcomplicated solutions I've ever heard.

Polygon Over a year ago

@JosephSible-ReinstateMonica I'm not proficient in this kind of stuff, and I didn't suggest that as the solution.

Polygon Over a year ago

@propre_poli streams are definetely what you should use, the other answer gives you a good solution. I looked through streams and it seems like it uses my file solution's flow but optimizes it.

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