Call .NET DLL generic instance method in .NET DLL app

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 .NET DLL like they were available in Java but invocation must be performed through Javonet SDK API.

Javonet allows you to pass any Java value type as argument to method from .NET DLL. 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 .NET DLL with generic methods

With Javonet it is possible to reference any custom .NET DLL and interact with its methods declared on types defined within that module almost the same as with any other Java library.

Snippet below represents the sample code from .NET DLL which contains generic methods.

namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        public static string GenericSampleStaticMethod<T>(T x, T y)
        {
        	return x + " and " + y;
        }
        
        public string GenericSampleMethod<T>(T x, T y)
        {
        	return x + " or " + y;
        }
        
        public K GenericSampleMethodWithTwoTypes<T, K>(T x)
        {
        	return default(K);
        }
	}
}
public static string GenericSampleStaticMethod<T>(T x, T y)
{
	return x + " and " + y;
}

public string GenericSampleMethod<T>(T x, T y)
{
	return x + " or " + y;
}

public K GenericSampleMethodWithTwoTypes<T, K>(T x)
{
	return default(K);
}

It is possible to invoke the declared methods from .NET DLL using following Java code:

import com.javonet.sdk.*;

public class SampleProgram {

    private static final String resourcesDirectory = ".";
    public static void main(String []args) {

        // use activate only once in your app
        Javonet.activate("your-license-key");
        
        // create called runtime context
        RuntimeContext calledRuntime = Javonet.inMemory().netcore();
        
        // set up variables
        String libraryPath = resourcesDirectory + "/TestClass.dll";
        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().execute();
        
        // get type for generic method
        InvocationContext targetType = calledRuntime.getType("System.Int32");
        
        // invoke type's method
        InvocationContext response = instance.invokeGenericMethod("GenericSampleMethod", targetType, 7, 5).execute();
        
        // get value from response
        String result = (String) response.getValue();
        
        // write result to console
        System.out.println(result);
     }
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        public static string GenericSampleStaticMethod<T>(T x, T y)
        {
        	return x + " and " + y;
        }
        
        public string GenericSampleMethod<T>(T x, T y)
        {
        	return x + " or " + y;
        }
        
        public K GenericSampleMethodWithTwoTypes<T, K>(T x)
        {
        	return default(K);
        }
	}
}
// use activate only once in your app
Javonet.activate("your-license-key");

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

// set up variables
String libraryPath = resourcesDirectory + "/TestClass.dll";
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().execute();

// get type for generic method
InvocationContext targetType = calledRuntime.getType("System.Int32");

// invoke type's method
InvocationContext response = instance.invokeGenericMethod("GenericSampleMethod", targetType, 7, 5).execute();

// get value from response
String result = (String) response.getValue();

// write result to console
System.out.println(result);

To invoke method which has more than one type specified:

import com.javonet.sdk.*;

public class SampleProgram {

    private static final String resourcesDirectory = ".";
    public static void main(String []args) {

        // use activate only once in your app
        Javonet.activate("your-license-key");
        
        // create called runtime context
        RuntimeContext calledRuntime = Javonet.inMemory().netcore();
        
        // set up variables
        String libraryPath = resourcesDirectory + "/TestClass.dll";
        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().execute();
        
        // get type for generic method
        InvocationContext targetType1 = calledRuntime.getType("System.String");
        InvocationContext targetType2 = calledRuntime.getType("System.Int32");
        
        // invoke type's method
        InvocationContext response = instance.invokeGenericMethod("GenericSampleMethodWithTwoTypes",
                new InvocationContext[] { targetType1, targetType2 }, "test").execute();
        
        // get value from response
        int result = (int) response.getValue();
        
        // write result to console
        System.out.println(result);
     }
}namespace TestClass
{
	public class TestClass
	{
		public TestClass() { }

        public static string GenericSampleStaticMethod<T>(T x, T y)
        {
        	return x + " and " + y;
        }
        
        public string GenericSampleMethod<T>(T x, T y)
        {
        	return x + " or " + y;
        }
        
        public K GenericSampleMethodWithTwoTypes<T, K>(T x)
        {
        	return default(K);
        }
	}
}
// use activate only once in your app
Javonet.activate("your-license-key");

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

// set up variables
String libraryPath = resourcesDirectory + "/TestClass.dll";
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().execute();

// get type for generic method
InvocationContext targetType1 = calledRuntime.getType("System.String");
InvocationContext targetType2 = calledRuntime.getType("System.Int32");

// invoke type's method
InvocationContext response = instance.invokeGenericMethod("GenericSampleMethodWithTwoTypes",
        new InvocationContext[] { targetType1, targetType2 }, "test").execute();

// get value from response
int result = (int) response.getValue();

// write result to console
System.out.println(result);

This snippet uses in memory runtime bridging to load the .NET DLL.
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 .NET DLL 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.

Call .NET DLL generic instance method in .NET DLL app

Custom .NET DLL with generic methods

Additional references