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fiware-cosmos-orion-flink-connector

This is a Flink connector for the Fiware Orion Context Broker. It has two parts:

• OrionSource: Source for receiving NGSIv2 events in the shape of HTTP messages from subscriptions.
• OrionSink: Sink for writing back to the Context Broker.

Installation

Download the JAR from the latest release. In your project directory run:

mvn install:install-file -Dfile=$(PATH_DOWNLOAD)/orion.flink.connector-1.0.jar -DgroupId=org.fiware.cosmos -DartifactId=orion.flink.connector -Dversion=1.0 -Dpackaging=jar

Add it to your pom.xml file inside the dependencies section

<dependency>
    <groupId>org.fiware.cosmos</groupId>
    <artifactId>orion.flink.connector</artifactId>
    <version>1.0</version>
</dependency>

Usage

OrionSource

• Import dependency

  import org.fiware.cosmos.orion.flink.connector.{OrionSource}
  

• Add source to Flink Environment. Indicate what port you want to listen to (e.g. 9001)

  val env = StreamExecutionEnvironment.getExecutionEnvironment
  val eventStream = env.addSource(new OrionSource(9001))
  

• Parse the received data

  val processedDataStream = eventStream.
      .flatMap(event => event.entities)
      // ...processing
  

  The received data is a DataStream of objects of the class NgsiEvent. This class has the following attributes:
  • creationTime: Timestamp of arrival.
  • service: Fiware service extracted from the HTTP headers.
  • servicePath: Fiware service path extracted from the HTTP headers.
  • entities: Sequence of entites included in the message. Each entity has the following attributes:
    • id: Identifier of the entity.
    • type: Node type.
    • attrs: Map of attributes in which the key is the attribute name and the value is an object with the following properties:
      • type: Type of value (Float, Int,...).
      • value: Value of the attribute.
      • metadata: Additional metadata.

OrionSink

• Import dependency

  import org.fiware.cosmos.orion.flink.connector.{OrionSink,OrionSinkObject,ContentType,HTTPMethod}
  

• Add sink to source

  val processedDataStream = eventStream.
   // ... processing
   .map(obj =>
      new OrionSinkObject(
          "{\"temperature_avg\": { \"value\":"+obj.temperature+", \"type\": \"Float\"}}", // Stringified JSON message
          "http://context-broker-url:8080/v2/entities/Room1", // URL
          ContentType.JSON, // Content type
          HTTPMethod.POST) // HTTP method
   )
  
  OrionSink.addSink( processedDataStream )
  

The sink accepts a DataStream of objects of the class OrionSinkObject. This class has 4 attributes:

• content: Message content in String format. If it is a JSON, you need to make sure to stringify it before sending it.
• url: URL to which the message should be sent.
• contentType: Type of HTTP content of the message. It can be ContentType.JSON or ContentType.Plain.
• method: HTTP method of the message. It can be HTTPMethod.POST, HTTPMethod.PUT or HTTPMethod.PATCH.

Production

Warning ⚠️

When packaging your code in a JAR, it is common to exclude dependencies like Flink and Scala since they are typically provided by the execution environment. Nevertheless, it is necessary to include this connector in your packaged code, since it is not part of the Flink distribution.