Work with JAR library exceptions in C# app

This article provides an introduction to cross-technology handling of exceptions. Exceptions in programming are events that occur during the execution of programs that disrupt the normal flow of instructions.

Any exception thrown by called technology is handled and thrown as any other exception in C# code. Details of exception depend on called technology, but in most cases final exception has all the information passed by called side.

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 exception handling

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 a chain of methods:

import java.util.*;
import java.lang.*;

public class TestClass {
    public TestClass() { }

        public static int divideBy(int x, int y) {
        	return divideBySecond(x, y);
        }
        
        public static int divideBySecond(int x, int y) {
        	return divideByThird(x, y);
        }
        
        public static int divideByThird(int x, int y) {
        	return x / y;
        }
}
public static int divideBy(int x, int y) {
	return divideBySecond(x, y);
}

public static int divideBySecond(int x, int y) {
	return divideByThird(x, y);
}

public static int divideByThird(int x, int y) {
	return x / y;
}

To invoke these methods in C#:

namespace SampleProgram {
	using Javonet.Netcore.Sdk;
	internal class Program {
		private static string resourcesDirectory = ".";
		static void Main(string[] args) {

			// use Activate only once in your app
			Javonet.Activate("your-license-key");
			
			// create called runtime context
			var calledRuntime = Javonet.InMemory().Jvm();
			
			// set up variables
			string libraryPath = resourcesDirectory + "/TestClass.jar";
			string className = "TestClass";
			
			// load custom library
			calledRuntime.LoadLibrary(libraryPath);
			
			// get type from the runtime
			var calledRuntimeType = calledRuntime.GetType(className).Execute();
			
			// invoke type's static method which throws exception
			try
			{
			    var response = calledRuntimeType.InvokeStaticMethod("divideBy", 10, 0).Execute();
			}
			catch (System.ArithmeticException e)
			{
			    // write result to console
			    System.Console.WriteLine(e.Message);
			    return;
			}
		}
	}
}import java.util.*;
import java.lang.*;

public class TestClass {
    public TestClass() { }

        public static int divideBy(int x, int y) {
        	return divideBySecond(x, y);
        }
        
        public static int divideBySecond(int x, int y) {
        	return divideByThird(x, y);
        }
        
        public static int divideByThird(int x, int y) {
        	return x / y;
        }
}
// use Activate only once in your app
Javonet.Activate("your-license-key");

// create called runtime context
var calledRuntime = Javonet.InMemory().Jvm();

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

// load custom library
calledRuntime.LoadLibrary(libraryPath);

// get type from the runtime
var calledRuntimeType = calledRuntime.GetType(className).Execute();

// invoke type's static method which throws exception
try
{
    var response = calledRuntimeType.InvokeStaticMethod("divideBy", 10, 0).Execute();
}
catch (System.ArithmeticException e)
{
    // write result to console
    System.Console.WriteLine(e.Message);
    return;
}

The last method throws exception which is handled and rethrown in C#. Then the exception in catched and printed.

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.