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, supporting both client and server-side development
• Active development and maintenance by the Eclipse Foundation
• Extensive documentation and examples available
• Supports various security features and encryption methods

Cons

• Steep learning curve for developers new to OPC UA
• Can be resource-intensive for embedded systems
• Limited support for older OPC specifications (e.g., OPC DA)
• Some users report occasional stability issues in complex scenarios

Code Examples

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

OpcUaClient client = OpcUaClient.create(
    "opc.tcp://localhost:4840",
    endpoints ->
        endpoints.stream()
            .filter(e -> e.getSecurityPolicyUri().equals(SecurityPolicy.None.getUri()))
            .findFirst(),
    configBuilder ->
        configBuilder
            .setApplicationName(LocalizedText.english("Eclipse Milo OPC UA Client"))
            .setApplicationUri("urn:eclipse:milo:examples:client")
            .build()
);

client.connect().get();

2. Reading a value from an OPC UA server:

NodeId nodeId = new NodeId(2, "HelloWorld/ScalarTypes/Int32");
DataValue value = client.readValue(0.0, TimestampsToReturn.Both, nodeId).get();
System.out.println("Value: " + value.getValue().getValue());

3. Writing a value to an OPC UA server:

NodeId nodeId = new NodeId(2, "HelloWorld/ScalarTypes/Int32");
DataValue newValue = new DataValue(new Variant(42));
StatusCode statusCode = client.writeValue(nodeId, newValue).get();
System.out.println("Write status: " + statusCode);

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>0.6.6</version>
    </dependency>
    <dependency>
        <groupId>org.eclipse.milo</groupId>
        <artifactId>sdk-server</artifactId>
        <version>0.6.6</version>
    </dependency>
</dependencies>

Then, you can create a simple OPC UA client as shown in the first code example above. For more detailed instructions and examples, refer to the official Eclipse Milo documentation.