Using node.js from Java

Try it Yourself!

Here is few things that you need:

• Download Graal VM from OTN (current sources were tested with GraalVM 0.19 - 0.23)
• Install Maven
• Get the sources: git clone https://github.com/jtulach/node4j

With these components, it should be easy to execute your first node.js application from Java:

$ cd node4j
$ JAVA_HOME=/path/to/graalvm/ mvn package exec:exec
Server listening on port 8080

Now you can connect to the http://localhost:8080/someurl and verify the application works. It should. But the best thing is that the application isn't written in JavaScript, but in Java:

package org.netbeans.demo.node4j;

import net.java.html.lib.Function;
import net.java.html.lib.node.http.Exports;
import net.java.html.lib.node.http.IncomingMessage;
import net.java.html.lib.node.http.ServerResponse;
import net.java.html.lib.node.http.Server;

public final class Main  {
    public static void main(String... args) {
        Server server = Exports.createServer((IncomingMessage request, ServerResponse response) -> {
            System.err.println("request for " + request.url());
            response.end("It works! Hit " + request.url());
            return null;
        });
        server.listen(8080, Function.newFunction((Function.A0<Void>) () -> {
            System.err.println("Server listening on port 8080");
            return null;
        }));
    }
}

All the power of node.js engine accessible from regular Java virtual machine via type-safe Java APIs!

Using NetBeans and JShell

The whole node4j project is a typical Maven project and you can work with it from any IDE that speaks Maven. However, if you download NetBeans IDE with built in support for JShell, we can do even more!

• Start the NetBeans 9 IDE (preview builds available): netbeans --jdkhome /path/to/jdk9
• Open the node4j project
• Configure it to use GraalVM 0.23 or newer in File/Properties
• Execute the project

A JShell console opens up in the editor and you can easily start using all the node.js features interactively from Java. Type:

cre

and press Ctrl-Space to invoke code completion. From the list of available choices select createServer method with one requestListener parameter. Following will be generated:

[19] -> createServer(requestListener)

press Ctrl-Space once again and let the IDE generate the lamda function body:

[19] -> createServer((p1, p2) -> {
            return null;
})

optionally rename p1 to in and p2 to out as that is the meaning of the callback parameters in this context. Type in a lamda body to generate a reply:

[19] -> createServer((p1, p2) -> {
    p2.end("Hello from Java!\n");
    return null;
})

after placing the caret at the end of the code snippet and pressing Enter, the snippet is evaluated:

|  Expression value is: [object Object]
|    assigned to temporary variable $53 of type Server

and the value is stored in variable $53. Try to use that variable, type:

$53.

and press Ctrl-Space to see methods available on this object. Choose listen method with one number parameter and bind the server to that port:

[20] -> $53.listen(2345)
|  Expression value is: 
|    assigned to temporary variable $64 of type Server

Your first interactive JShell+Node.js session is done. Connect to http://localhost:2345 to verify the server works.