Create NodeJs package instance and call instance method in Java app

This article provides an introduction to cross-technology creation of instances of classes and invocation of instance methods.

With Javonet you can interact with classes from NodeJs package like they were available in Java but invocation must be performed through Javonet SDK API, passing type and method name as string.

Javonet allows you to pass any Java value type as argument to instance method from NodeJs package. In example: int, float, string, char, long and other. For reference type arguments (instances of other classes) you can create such instance with Javonet and pass the Invocation Context variable referencing that object as argument of static method invocation.

Use custom NodeJs package classes in Java application

With Javonet it is possible to reference any custom NodeJs package and interact with public methods declared on types defined within that module almost the same as with any other Java library.

This section present sample custom NodeJs package with class declaring methods and Javonet SDK syntax required to create object and invoke that methods and consume the results in Java.

Snippet below represents the sample code from NodeJs package which contains class and its methods:

const fs = require('fs').promises;

class TestClass {

    static multiplyByTwo(a) {
    	return 2 * a;
    }
    
    multiplyTwoNumbers(a, b) {
    	return a * b
    }
}

module.exports = TestClassstatic multiplyByTwo(a) {
	return 2 * a;
}

multiplyTwoNumbers(a, b) {
	return a * b
}

It is possible to invoke one of the declared instance methods from NodeJs package using following Java code.

import com.javonet.sdk.*;

public class SampleProgram {

    private static final String resourcesDirectory = ".";
    public static void main(String []args) {

        // use activate only once in your app
        Javonet.activate("your-license-key");
        
        // create called runtime context
        RuntimeContext calledRuntime = Javonet.inMemory().nodejs();
        
        // set up variables
        String libraryPath = resourcesDirectory + "/TestClass.js";
        String className = "TestClass";
        
        // load custom library
        calledRuntime.loadLibrary(libraryPath);
        
        // get type from runtime
        InvocationContext calledRuntimeType = calledRuntime.getType(className).execute();
        
        // create type's instance
        InvocationContext instance = calledRuntimeType.createInstance().execute();
        
        // invoke instance's method
        InvocationContext response = instance.invokeInstanceMethod("multiplyTwoNumbers", 5, 4).execute();
        
        // get value from response
        int result = (int) response.getValue();
        
        // write result to console
        System.out.println(result);
     }
}const fs = require('fs').promises;

class TestClass {

    static multiplyByTwo(a) {
    	return 2 * a;
    }
    
    multiplyTwoNumbers(a, b) {
    	return a * b
    }
}

module.exports = TestClass// use activate only once in your app
Javonet.activate("your-license-key");

// create called runtime context
RuntimeContext calledRuntime = Javonet.inMemory().nodejs();

// set up variables
String libraryPath = resourcesDirectory + "/TestClass.js";
String className = "TestClass";

// load custom library
calledRuntime.loadLibrary(libraryPath);

// get type from runtime
InvocationContext calledRuntimeType = calledRuntime.getType(className).execute();

// create type's instance
InvocationContext instance = calledRuntimeType.createInstance().execute();

// invoke instance's method
InvocationContext response = instance.invokeInstanceMethod("multiplyTwoNumbers", 5, 4).execute();

// get value from response
int result = (int) response.getValue();

// write result to console
System.out.println(result);

In code snippet above you can see how easily you can activate Javonet and instruct it using inMemory() method to create new RuntimeContext that will run nodejs-package runtime within your current process. Next with addLibrary method it triggers the load of required nodejs-package module and allows you to interact with any classes and their methods defined in that package.

Further call to createInstance() allows to create instance of class. Calls to invokeInstanceMethod() allows to call "multiplyTwoNumbers" nodejs-package instance method and pass the value type arguments. With Javonet you can invoke methods with any number and any type of arguments including value type arguments, reference type arguments, arrays and collections.

You can receive and further process and type of result returned by called nodejs-package method, regardless if it is reference type that will get returned as another instance of Invocation Context that you can use for further interaction, or value type that you can obtain as java value with getValue() method.

Use framework classes in Java application

The same steps are required to use types and methods from standard NodeJs package:

The same operation can be performed remotely by just changing the new Runtime Context invocation from in memory to tcp that will create and interact with your NodeJs package objects on any remote node, container or service that hosts Javonet Code Gateway. This way you can preserve the same logic in your application and instantly switch between monolithic and microservices architecture without the need to implement the integration layer based on web services or other remote invocation methods.

Read more about use cases and software architecture scenarios where Javonet runtime bridging technology can support your development process.