Heron

Tuple is Heron’s core data type. All data that is fed into a Heron topology via spouts and then processed by bolts consists of tuples.

Heron has a Tuple interface for working with tuples. Heron Tuples can hold values of any type; values are accessible either by providing an index or a field name.

Using Tuples

Heron’s Tuple interface contains the methods listed in the Javadoc definition.

Accessing Primitive Types By Index

Heron Tuples support a wide variety of primitive Java types, including strings, Booleans, byte arrays, and more. getString method, for example, takes an integer index and returns either a string or null if no string value is present at that index. Analogous methods can be found in the Javadoc.

Accessing Primitive Types By Field

In addition to being accessible via index, values stored in Heron tuples are accessible via field name as well. The getStringByField method, for example, takes a field name string and returns either a string or null if no string value is present for that field name. Analogous methods can be found in the Javadoc.

Using Non-primitive Types

In addition to primitive types, you can access any value in a Heron Tuple as a Java Object. As for primitive types, you can access Objects on the basis of an index or a field name. The following methods return either an Object or null if no object is present:

You can also retrieve all objects contained in a Heron Tuple as a Java List using the getValues method.

User-defined Types

You use Heron tuples in conjunction with more complex, user-defined types using type casting, provided that you’ve created and registered a custom serializer for the type. Here’s an example (which assumes that a serializer for the type Tweet has been created and registered):

public void execute(Tuple input) { // The following return null if no value is present or throws a // ClassCastException if type casting fails: Tweet tweet = (Tweet) input.getValue(0); List allTweets = input.getValues(); }

More info on custom serialization can be found in Creating Custom Tuple Serializers.

Fields

The getFields method returns a Fields object that contains all of the fields in the tuple. More on fields can be found below.

Other Methods

There are additional methods available for determining the size of Heron Tuples, extracting contextual information, and more. For a full listing of methods, see the Javadoc.

Fields

From the methods in the list above you can see that you can retrieve single values from a Heron tuple on the basis of their index. You can also retrieve multiple values using a Fields object, which can be initialized either using varargs or a list of strings:

// Using varargs Fields fruits = new Fields("apple", "orange", "banana"); // Using a list of strings List fruitNames = new LinkedList(); fruitNames.add("apple"); // Add "orange" and "banana" as well Fields fruits = new Fields(fruitNames);

You can then use that object in conjunction with a tuple:

public void execute(Tuple input) { List