Call C++ generic instance method from JAR library

This article provides an introduction to cross-technology invocation of instance generic methods. Generic methods in C# (.NET) and Java technologies are methods that are declared with the type parameter in its signature, allowing it to be used with any data type. It is described in detail in article about generic methods in .NET and article about generic methods in Java.

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.

With Javonet you can interact with generic instance methods from JAR library like they were available in C++ but invocation must be performed through Javonet SDK API.

Javonet allows you to pass any C++ value type as argument to method from JAR library. 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 method invocation.

Custom JAR library with C++ generic methods

With Javonet it is possible to reference any custom JAR library and interact with its methods 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 which contains generic methods.

public static <T> String genericSampleStaticMethod(T x, T y) {
	return x.toString() + " and " + y.toString();
}

public <T> String genericSampleMethod(T x, T y) {
	return x.toString() + " or " + y.toString();
}

public <T, K> String genericSampleMethodWithTwoTypes(T x) {
	return "genericSampleMethodWithTwoTypes invoked";
}

It is possible to invoke the declared methods from JAR library using following C++ code:

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 generic method
auto response = instance->
	InvokeGenericMethod("genericSampleMethod", { 7, 5 })->
	Execute();

// get value from response
auto result = std::any_cast<std::string>(response->GetValue());

// write result to console
std::cout << result << std::endl;

This snippet uses in memory runtime bridging to load the JAR library.
Next, type is specified and instance of class is created.
Next, generic instance method is invoked.
While calling .NET generic method it is necessary to pass method name, type and arguments.
While calling Java generic method it is necessary to pass method name and arguments.

To invoke method which has more than one type specified:

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 generic method
auto response = instance->
	InvokeGenericMethod("genericSampleMethodWithTwoTypes", 7)->
	Execute();

// get value from response
auto result = std::any_cast<std::string>(response->GetValue());

// write result to console
std::cout << result << std::endl;

This snippet uses in memory runtime bridging to load the JAR library.
Next, type is specified and instance of class is created.
Next, generic instance method is invoked.
While calling .NET generic method it is necessary to pass method name, type and arguments.
While calling Java generic method it is necessary to pass method name and arguments.
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