Eclipse Milo is an open-source implementation of OPC UA (Open Platform Communications Unified Architecture) for Java. It provides a complete stack for building OPC UA clients and servers, enabling industrial automation and IoT applications to communicate using this standardized protocol.

Pros

• Comprehensive implementation of OPC UA in Java
• Actively maintained with regular updates and bug fixes
• Supports both client and server-side development
• Well-documented with examples and extensive JavaDoc

Cons

• Steep learning curve for those unfamiliar with OPC UA
• Can be complex to set up and configure for advanced use cases
• Limited support for some newer OPC UA features compared to commercial alternatives
• Performance may not be optimal for high-throughput scenarios

Code Examples

1. Creating an OPC UA client and connecting to a server:

OpcUaClientConfigBuilder cfg = new OpcUaClientConfigBuilder();
cfg.setEndpoint(new EndpointDescription(serverUrl, EndpointConfiguration.DEFAULT_CONFIGURATION));

OpcUaClient client = OpcUaClient.create(cfg.build());
client.connect().get();

2. Reading a value from a node:

NodeId nodeId = new NodeId(2, "MyVariable");
DataValue value = client.readValue(0.0, TimestampsToReturn.Both, nodeId).get();
System.out.println("Value: " + value.getValue().getValue());

3. Writing a value to a node:

NodeId nodeId = new NodeId(2, "MyVariable");
DataValue newValue = new DataValue(new Variant(42));
StatusCode result = client.writeValue(nodeId, newValue).get();
System.out.println("Write result: " + result);

4. Subscribing to data changes:

UaSubscription subscription = client.getSubscriptionManager().createSubscription(1000.0).get();
ReadValueId readValueId = new ReadValueId(nodeId, AttributeId.Value.uid(), null, QualifiedName.NULL_VALUE);
MonitoringParameters parameters = new MonitoringParameters(uint(1), 1000.0, null, uint(10), true);
MonitoredItemCreateRequest request = new MonitoredItemCreateRequest(readValueId, MonitoringMode.Reporting, parameters);

subscription.createMonitoredItems(TimestampsToReturn.Both, Arrays.asList(request), (item, id) -> {
    item.setValueConsumer(value -> System.out.println("Value received: " + value.getValue().getValue()));
}).get();

Getting Started

To use Eclipse Milo in your Java project, add the following dependencies to your Maven pom.xml:

<dependencies>
    <dependency>
        <groupId>org.eclipse.milo</groupId>
        <artifactId>sdk-client</artifactId>
        <version>0.6.8</version>
    </dependency>
    <dependency>
        <groupId>org.eclipse.milo</groupId>
        <artifactId>sdk-server</artifactId>
        <version>0.6.8</version>
    </dependency>
</dependencies>

For Gradle, add these to your build.gradle:

dependencies {
    implementation 'org.eclipse.milo:sdk-client:0.6.8'
    implementation 'org.eclipse.milo:sdk-server:0.6.8'
}

After adding the dependencies, you can start using Eclipse Milo in your Java code as shown in the examples above.