Retrieve Python package array in Java app

This article shows how to retrieve array from called technology.

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 Python package with array handling

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

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

def get_1d_array(self):
    return ["one", "two", "three", "four", "five"]

def get_2d_array(self):
    return [["S00", "S01"], ["S10", "S11"]]

def add_array_elements_and_multiply(self, my_array, my_value):
    return sum(my_array) * my_value

Retrieve Python package array in Java application

With Javonet SDK it is possible to retrieve array from called technology and cast it to Java array.

I code in:
// use activate only once in your app
Javonet.activate("your-license-key");

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

// set up variables
// path to directory with .py files
String libraryPath = resourcesDirectory;
String className = "TestClass.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(0, 1).execute();

// invoke instance's method
InvocationContext arrayReference = instance.invokeInstanceMethod("get_1d_array").execute();

// get value from array reference
Object[] response = arrayReference.retrieveArray();

// write to string array
String[] result = java.util.Arrays.copyOf(response, response.length, String[].class);

// write result to console
System.out.println(String.join("\t", result));

In the snippet above, get1DArray method is used to get reference to 1D array from Python package. Method retrieveArray is used to get the whole array from called technology and save it to local variable.

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 Python 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.

Additional references