node-red-contrib-jar-func

Node-RED node to run executable-jar file

Using the node, Node-RED users can run any JVM based code, such as Java, Kotlin, Scala programs.

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How to setup the Java environment

(1) Download and install Java Development Kit

http://www.oracle.com/technetwork/java/javase/downloads/jdk10-downloads-4416644.html

(2) Set environment variables, JAVA_HOME and PATH to enable java and javac command

http://www.baeldung.com/java-home-on-windows-7-8-10-mac-os-x-linux

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How to interact with the jar program

While this node is created, it will start running the specified jar program using the following command:
java -jar {jar-file-name}
The jar program can keep running without exiting.
Any message arriving at the input of this node will be transmitted to the stdin of the jar program with JSON fromat, one line at a time.
Each line of messages printed by the jar program's stdout will be tried to parse as JSON, if success, it will appear at the output of this node.

Example Hello.java

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SerializerFeature;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Hello {

    public static void main(String[] args) {
        @SuppressWarnings("WeakerAccess")
        class Result {
            public String topic;
            public String payload;
        }

        BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
        //noinspection InfiniteLoopStatement
        for (;;) {
            try {
                String line = stdin.readLine();
                JSONObject obj = JSON.parseObject(line);
                String payload = obj.get("payload").toString();

                Result result = new Result();
                result.topic = "Log";
                result.payload = "输入的payload=" + payload;	// this line contains Chinese characters.

                System.out.print("it works");	// the output will be parsed line by line,
                Thread.sleep(200);		// no matter timing.
                System.out.println(" fine!");	// this will be shown on node-red console but not to output
                                                // because it it not a valid JSON string.

                System.out.println(JSON.toJSONString(result,
                        // with unicode, Chinese characters can be displayed correctly.
                        SerializerFeature.BrowserCompatible		// BrowserCompatible ==> unicode encoding.
                ));	// this message will appear at the output of this node.

                System.out.println("This is a Java program.");	// only to node-red console
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

}