org.apache.storm.trident.operation

Interface Function

All Superinterfaces:

EachOperation, Operation, Serializable

All Known Implementing Classes:

BaseFunction, CombinerAggregatorInitImpl, ConsumerExecutor, FilterExecutor, FlatMapFunctionExecutor, MapFunctionExecutor, MqttPublishFunction, PrintFunction, PrintFunction, PrintFunction, Split, StringLength, TridentReach.ExpandList, TridentWordCount.Split, TuplifyArgs

public interface Function
extends EachOperation

A function takes in a set of input fields and emits zero or more tuples as output. The fields of the output tuple are appended to the original input tuple in the stream. If a function emits no tuples, the original input tuple is filtered out. Otherwise, the input tuple is duplicated for each output tuple.

For example, if you have the following function:

```java public class MyFunction extends BaseFunction { public void execute(TridentTuple tuple, TridentCollector collector) { for(int i=0; i < tuple.getInteger(0); i++) { collector.emit(new Values(i)); } } } ```

Now suppose you have a stream in the variable `mystream` with the fields `["a", "b", "c"]` with the following tuples:

``` [1, 2, 3] [4, 1, 6] [3, 0, 8] ``` If you had the following code in your topology definition:

```java mystream.each(new Fields("b"), new MyFunction(), new Fields("d"))) ```

The resulting tuples would have the fields `["a", "b", "c", "d"]` and look like this:

``` [1, 2, 3, 0] [1, 2, 3, 1] [4, 1, 6, 0] ```

In this case, the parameter `new Fields("b")` tells Trident that you would like to select the field "b" as input to the function, and that will be the only field in the Tuple passed to the `execute()` method. The value of "b" in the first tuple (2) causes the for loop to execute twice, so 2 tuples are emitted. similarly the second tuple causes one tuple to be emitted. For the third tuple, the value of 0 causes the `for` loop to be skipped, so nothing is emitted and the incoming tuple is filtered out of the stream.

### Configuration If your `Function` implementation has configuration requirements, you will typically want to extend BaseFunction and override the Operation.prepare(Map, TridentOperationContext) method to perform your custom initialization.

### Performance Considerations Because Trident Functions perform logic on individual tuples -- as opposed to batches -- it is advisable to avoid expensive operations such as database operations in a Function, if possible. For data store interactions it is better to use a State or QueryFunction implementation since Trident states operate on batch partitions and can perform bulk updates to a database.

Method Summary

Modifier and Type	Method and Description
void	execute(TridentTuple tuple, TridentCollector collector) Performs the function logic on an individual tuple and emits 0 or more tuples.

Methods inherited from interface org.apache.storm.trident.operation.Operation

cleanup, prepare

Method Detail

execute

void execute(TridentTuple tuple,
             TridentCollector collector)

Performs the function logic on an individual tuple and emits 0 or more tuples.

Parameters:

tuple - The incoming tuple

collector - A collector instance that can be used to emit tuples