A User Defined Stream Source is a Java-based User Defined Function (UDF) that generates a stream of data records which can be used by the UDF Stream Source Assembly in HGrid247.

Creating a User Defined Stream Source

To create a custom stream source, you must:

• Create a Java class that extends the abstract class:

          com.labs247.function.StreamSource
          

• Implement the required method:

          public abstract List<Comparable> run()
  

  This method generates and returns a record (a list of values) that will be sent to the next assembly in the data pipeline.

Methods Available in StreamSource

The class com.labs247.function.StreamSource provides several inherited methods:

1. public abstract List<Comparable> run()
   Called repeatedly to generate a new record.
   Returns a List of Comparable values that represent one data record.
2. public String getParameter()
   Returns the parameter passed to the stream source.
3. public void open()
   Called after the object is created.
   Usually used for initialization (e.g., opening connections).
4. public void close()
   Called when the object is destroyed.
   Used for cleanup operations.
5. public long currentEventTime()
   Returns the current time in milliseconds.
   Used to assign Event Time to generated records.
   This method can be overridden if a custom event time is needed.

Example: Random Number Stream Source

This example generates a stream of random integers.

    package hgrid.plugins.source;

    import com.labs247.function.StreamSource;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Random;

    public class RandomNumberSource extends StreamSource {
        Random random = new Random();
        @Override
        public List <Comparable> run() {
            List<Comparable> list=new ArrayList<>();
            list.add(random.nextInt()); 
            return list;   
        }   
    }

Explanation of the Example

1. The class RandomNumberSource extends StreamSource.
2. A Random object generates random numbers.
3. The run() method:
   • Creates a new list.
   • Adds a random integer to the list.
   • Returns the list as a record.
4. Each time run() executes, a new random number record is produced.

Example output stream:

    1034
    -252
    781
    912
    -64

Deploying the UDF Stream Source

To make the custom source appear in the HGrid247-3.5 GUI:

• Compile the Java class.
• Package it into a JAR file.
• Place the JAR file inside the plugins folder.

    HGrid247-3.5/
    ├── plugins/
    │     └── RandomNumberSource.jar

After restarting HGrid247, the UDF Stream Source will be available in the GUI.