Use instance fields and properties from JAR library in Ruby app

This article provides an introduction to cross-technology handling of static fields and properties.
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 instance field and properties from JAR library like they were available in Ruby but invocation must be performed through Javonet SDK API.

Javonet allows you to pass any Ruby 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 instance fields and properties

With Javonet it is possible to reference any custom JAR library and interact with public instance fields and properties declared on types defined within that module almost the same as with any other Ruby library.

Snippet below represents the sample code from JAR library which contains class with fields:

public int publicValue;
private int privateValue;
public static int staticValue = 3;

public TestClass(int publicValue, int privateValue) {
	this.publicValue = publicValue;
	this.privateValue = privateValue;
}

It is possible to get one of the declared instance fields from JAR library using following Ruby code.

I code in:
# use activate only once in your app
Javonet.activate('your-license-key')

# create called runtime context
called_runtime = Javonet.in_memory.jvm

# set up variables
library_path = "#{resources_directory}/TestClass.jar"
class_name = 'TestClass'

# load custom library
called_runtime.load_library(library_path)

# get type from the runtime
called_runtime_type = called_runtime.get_type(class_name).execute

# create type's instance
instance = called_runtime_type.create_instance(18, 19).execute

# get instance's field
response = instance.get_instance_field('publicValue').execute

# get value from response
result = response.get_value

# write result to console
puts result

This uses in memory runtime bridging to load the JAR library, and next retrieves reference to specific type and gets the instance field. Result of the invocation is returned as regular Ruby value and can be used for further processing. It is possible to set one of the declared instance fields from JAR library using following Ruby code.

I code in:
# use activate only once in your app
Javonet.activate('your-license-key')

# create called runtime context
called_runtime = Javonet.in_memory.jvm

# set up variables
library_path = "#{resources_directory}/TestClass.jar"
class_name = 'TestClass'

# load custom library
called_runtime.load_library(library_path)

# get type from the runtime
called_runtime_type = called_runtime.get_type(class_name).execute

# create type's instance
instance = called_runtime_type.create_instance(18, 19).execute

# set instance field
instance.set_instance_field('publicValue', 44).execute

# get instance's field
response = instance.get_instance_field('publicValue').execute

# get value from response
result = response.get_value

# write result to console
puts result

This uses in memory runtime bridging to load the JAR library, and next retrieves reference to specific type, then sets and gets the instance field. Result of the invocation is returned as regular Ruby value and can be used for further processing.

Framework instance fields and properties

The same steps are required to get types and fields from framework JAR library:

I code in:
# use activate only once in your app
Javonet.activate('your-license-key')

# create called runtime context
called_runtime = Javonet.in_memory.jvm

# get type from the runtime
called_runtime_type = called_runtime.get_type('java.sql.DriverPropertyInfo').execute

# create type's instance
instance = called_runtime_type.create_instance('sample value', 'sample value 2').execute

# get instance's field
response = instance.get_instance_field('name').execute

# get value from response
result = response.get_value

# write result to console
puts result

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