Invoke JAR library static methods in C++ app

This article provides an introduction to cross-technology invocation of static methods.

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 static methods from JAR library like they were available in C++ but invocation must be performed through Javonet SDK API, passing the name of the target method as String.

Javonet allows you to pass any C++ value type as argument to static method from JAR library. 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 JAR library static methods in C++ application

With Javonet it is possible to reference any custom JAR library and interact with public static 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 class and its methods: 

public static int multiplyByTwo(int a) {
    return 2 * a;
}

public int multiplyTwoNumbers(int a, int b) {
    return a * b;
}

It is possible to invoke one of the declared static 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();

// invoke type's static method 
auto response = calledRuntimeType->InvokeStaticMethod("multiplyByTwo", 25)->Execute();

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

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

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 jar-library runtime within your current process. Next with addLibrary method it triggers the load of required jar-library module and allows you to interact with any classes and their static methods defined in that package.

Further calls to invokeStaticMethod() allows to call "multiplyByTwo" jar-library static 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 jar-library 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 cpp value with getValue() method.

Use framework static methods in C++ application

With Javonet you can interact not only with any custom jar-library module but also with any jar-library framework objects. The same steps are required to use types and methods from standard JAR library framework class:

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

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

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType("java.lang.Math")->Execute();

// invoke type's static method 
auto response = calledRuntimeType->InvokeStaticMethod("abs", -50)->Execute();

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

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

In sample above you see how the Javonet allows to create an instance of JAR library Math class and interact with its static abs method. 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