User defined procedures and functions are written as Java classes

Example user defined function to join list of strings with a separator

example.join(['Hello', 'NODES'], ',')

Compile and package project with Maven to produce plugin JAR file

mvn clean package → target/example-1.0.0.jar

👉 Test

public class Join {
  
  @UserFunction
  @Description("example.join(['a','b'], ',')) 
  public String join(
    @Name("strings") List<String> strings, 
    @Name("delimiter") String delimiter) { 

    if (strings == null || delimiter == null) 
      return null;

    return String.join(delimiter, strings); 
  }
}