Passing array from Python as method argument to JAR library

This article shows how to pass array as an argument.

Javonet allows you to reference and use modules or packages written in (Java/Kotlin/Groovy/Clojure, C#/VB.NET, Ruby, Perl, Python, JavaScript/TypeScript) like they were created in your technology. If have not yet created your first project check Javonet overview and quick start guides for your technology.

Custom JAR library with method accepting array

With Javonet it is possible to reference any custom JAR library and interact with arrays declared on types defined within that module almost the same as with any other Python library.

Snippet below represents the sample code from JAR library that has methods which return or process the arrays:

public String[] get1DArray() {
	return new String[]{"one", "two", "three", "four", "five"};

public String[][] get2DArray() {
	return new String[][]{{"S00", "S01"},{"S10", "S11"}};

public double addArrayElementsAndMultiply(Double[] myArray, double myValue) {
	Double sum = 0.0;
	for (Double value : myArray) {
		sum += value;
	return sum * myValue;

With Javonet SDK it is possible to pass array as an argument to one of this method.

Passing array from Python

# use Activate only once in your app

# create called runtime context
called_runtime = Javonet.in_memory().jvm()

# set up variables
library_path = resources_directory + '/TestClass.jar'
class_name = 'TestClass'

# load custom library

# get type from the runtime
called_runtime_type = called_runtime.get_type(class_name).execute()

# create type's instance
instance = called_runtime_type.create_instance().execute()

# invoke instance's method
response = instance.invoke_instance_method("addArrayElementsAndMultiply", [12.22, 98.22, -10.44], 9.99).execute()

# get value from response
result = response.get_value()

# write result to console

In the snippet above, addArrayElementsAndMultiply method needs array to be the first argument. Depending on called technology, the array may need to have a specific type, f. e. array of doubles. In this case, proper cast is needed before passing the array from Python.

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 JAR library 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.