Retrieve JAR library array in C++ 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 JAR library with array handling

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 C++ 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;
}

Retrieve JAR library array in C++ application

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

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

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Jvm();

// set up variables
auto libraryPath = resourcesDirectory + "/TestClass.jar";
auto className = "TestClass";

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance()->Execute();

// invoke instance's method
auto arrayReference = instance->InvokeInstanceMethod("get1DArray")->Execute();

// get array from reference
auto response = arrayReference->RetrieveArray();

auto result = std::any_cast<std::deque<std::any>>(response);

auto resultArray = std::vector<std::string>(result.size());

for (int i = 0; i < result.size(); i++) {
	resultArray[i] = std::any_cast<std::string>(result[i]);
	// write result to console
	std::cout << resultArray[i] << "\t";
}

In the snippet above, get1DArray method is used to get reference to 1D array from JAR library. 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 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.

Additional references