/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package storm.trident.operation;
import storm.trident.tuple.TridentTuple;
import java.util.Map;
/**
* 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
* {@link org.apache.storm.trident.operation.BaseFunction} and override the
* {@link org.apache.storm.trident.operation.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 {@link org.apache.storm.trident.state.State} or
* {@link org.apache.storm.trident.state.QueryFunction} implementation since Trident states operate on batch partitions
* and can perform bulk updates to a database.
*
*
*/
public interface Function extends EachOperation {
/**
* Performs the function logic on an individual tuple and emits 0 or more tuples.
*
* @param tuple The incoming tuple
* @param collector A collector instance that can be used to emit tuples
*/
void execute(TridentTuple tuple, TridentCollector collector);
}