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Once you have the OPC Gateway running, it's possible access the OPC Legacy server from any system using pure Java code. Here's a sample that shows how to do that.

import com.ergotech.util.SimulationManager;
import com.ergotech.util.TargetLicenseManager;
import com.ergotech.vib.exceptions.BadParameterException;
import com.ergotech.vib.exceptions.VIBUpdateFailedException;
import com.ergotech.vib.servers.SimpleDataSource;
import com.ergotech.vib.servers.opc.opcclient.OPC;
import com.ergotech.vib.utils.DataSourceContainer;
import com.ergotech.vib.valueobjects.ValueChangedEvent;
import com.ergotech.vib.valueobjects.ValueObjectInterface;
 
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
 
public class OPCDemo {
 
    public static void main(String[] args) throws InterruptedException {
        OPCDemo opcDemo = new OPCDemo();
 
        // Configure the license, required for OPC component to function.
        opcDemo.setupLicense();
 
        // Disable simulation mode to connect to the actual OPC server.
        SimulationManager.getSimulationManager().setSimulating(false);
 
        // Initialize and start the OPC setup.
        opcDemo.setupOpc();
 
        // Keep the application running for 5 minutes to receive updates from the OPC server.
        Thread.sleep(1000 * 60 * 5);
    }
 
    public void setupLicense() {
        try (InputStream license = Files.newInputStream(Path.of("resources/MIX.trg"))) {
            // Initialize the license manager with the appropriate target.
            final TargetLicenseManager manager = new TargetLicenseManager("MIX",
                    license,
                    OPCDemo.class.getClassLoader());
 
            // Set the license manager for components.
            SimpleDataSource.setClassLicenseManager(manager);
        } catch (Exception e) {
            // Handle any failure during license setup.
            throw new RuntimeException("Failed to setup license", e);
        }
    }
 
    public void setupOpc() {
        DataSourceContainer container;
 
        try {
            // Create a new OPC container to hold the OPC components.
            container = DataSourceContainer.getRootContainer().createNewChildContainer("OPCExample");
        } catch (BadParameterException e) {
            // Occurs if a container with the same name already exists.
            throw new RuntimeException("Failed to create OPC container", e);
        }
 
        OPC opc = new OPC();
 
        try {
            // Assign a unique, case-insensitive name to the OPC component.
            opc.setName("OPC");
 
            // Assign the host and item to connect to in the OPC server.
            opc.setHost("localhost"); // the host that is running the OPCGateway
            opc.setItem("GEMToolSimulator.VIDs.SVIDs.Temperature");
        } catch (BadParameterException e) {
            // Handle invalid configuration for the OPC component.
            throw new RuntimeException("Invalid OPC configuration", e);
        }
 
        try {
            // Add the configured OPC component to the container.
            container.addComponent(opc, opc.getName());
        } catch (BadParameterException e) {
            // Occurs if a component with the same name is already added to the container.
            throw new RuntimeException("Failed to add OPC component to container", e);
        }
 
        // Register a listener to handle value change events from the OPC server.
        opc.addValueChangedListener(new ValueChangedCallback());
 
        try {
            // Initialize and start the OPC component.
            opc.init();
            opc.start();
        } catch (BadParameterException | VIBUpdateFailedException e) {
            // Handle any failure during initialization or startup.
            throw new RuntimeException("Failed to start OPC component", e);
        }
 
        // Access current values as various types
        System.out.println("Current value as String: " + opc.getValueObject().getStringValue());
        System.out.println("Current value as Double: " + opc.getValueObject().getDoubleValue());
        System.out.println("Current value as Float: " + opc.getValueObject().getFloatValue());
        System.out.println("Current value as Integer: " + opc.getValueObject().getIntValue());
        System.out.println("Current value as Long: " + opc.getValueObject().getLongValue());
        System.out.println("Current value as Boolean: " + opc.getValueObject().getBoolValue());
    }
 
    // Callback to process value changes from the OPC component.
    public static class ValueChangedCallback {
 
        // Any object with a method "valueInput(ValueChangedEvent) can be used a callback
        public void valueInput(ValueChangedEvent valueChangedEvent) {
            // Logic to handle changes in OPC data, triggered whenever the OPC value changes.
            ValueObjectInterface valueObject = valueChangedEvent.getValueObject();
            System.out.println("Value Changed: " + valueObject + " [quality: " + valueObject.getQuality() + "]");
        }
    }
 
}