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| <div class="sub-title"><span class="package-label-in-type">Package</span> <a href="package-summary.html">org.apache.storm.trident.operation</a></div> |
| <h1 title="Interface Function" class="title">Interface Function</h1> |
| </div> |
| <section class="class-description" id="class-description"> |
| <dl class="notes"> |
| <dt>All Superinterfaces:</dt> |
| <dd><code><a href="EachOperation.html" title="interface in org.apache.storm.trident.operation">EachOperation</a></code>, <code><a href="Operation.html" title="interface in org.apache.storm.trident.operation">Operation</a></code>, <code><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/Serializable.html" title="class or interface in java.io" class="external-link">Serializable</a></code></dd> |
| </dl> |
| <dl class="notes"> |
| <dt>All Known Implementing Classes:</dt> |
| <dd><code><a href="BaseFunction.html" title="class in org.apache.storm.trident.operation">BaseFunction</a></code>, <code><a href="impl/CombinerAggregatorInitImpl.html" title="class in org.apache.storm.trident.operation.impl">CombinerAggregatorInitImpl</a></code>, <code><a href="impl/ConsumerExecutor.html" title="class in org.apache.storm.trident.operation.impl">ConsumerExecutor</a></code>, <code><a href="impl/FilterExecutor.html" title="class in org.apache.storm.trident.operation.impl">FilterExecutor</a></code>, <code><a href="impl/FlatMapFunctionExecutor.html" title="class in org.apache.storm.trident.operation.impl">FlatMapFunctionExecutor</a></code>, <code><a href="impl/MapFunctionExecutor.html" title="class in org.apache.storm.trident.operation.impl">MapFunctionExecutor</a></code>, <code><a href="../../redis/trident/PrintFunction.html" title="class in org.apache.storm.redis.trident">PrintFunction</a></code>, <code><a href="../testing/Split.html" title="class in org.apache.storm.trident.testing">Split</a></code>, <code><a href="../testing/StringLength.html" title="class in org.apache.storm.trident.testing">StringLength</a></code>, <code><a href="../../starter/trident/TridentReach.ExpandList.html" title="class in org.apache.storm.starter.trident">TridentReach.ExpandList</a></code>, <code><a href="../../starter/trident/TridentWordCount.Split.html" title="class in org.apache.storm.starter.trident">TridentWordCount.Split</a></code>, <code><a href="../testing/TuplifyArgs.html" title="class in org.apache.storm.trident.testing">TuplifyArgs</a></code></dd> |
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| <div class="type-signature"><span class="modifiers">public interface </span><span class="element-name type-name-label">Function</span><span class="extends-implements"> |
| extends <a href="EachOperation.html" title="interface in org.apache.storm.trident.operation">EachOperation</a></span></div> |
| <div class="block">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. |
| |
| <p>For example, if you have the following function: |
| |
| <p>```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)); } } } |
| ``` |
| |
| <p>Now suppose you have a stream in the variable `mystream` with the fields `["a", "b", "c"]` with the following tuples: |
| |
| <p>``` [1, 2, 3] [4, 1, 6] [3, 0, 8] ``` If you had the following code in your topology definition: |
| |
| <p>```java mystream.each(new Fields("b"), new MyFunction(), new Fields("d"))) ``` |
| |
| <p>The resulting tuples would have the fields `["a", "b", "c", "d"]` and look like this: |
| |
| <p>``` [1, 2, 3, 0] [1, 2, 3, 1] [4, 1, 6, 0] ``` |
| |
| <p>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. |
| |
| <p>### Configuration If your `Function` implementation has configuration requirements, you will typically want to extend <a href="BaseFunction.html" title="class in org.apache.storm.trident.operation"><code>BaseFunction</code></a> and override the <a href="Operation.html#prepare(java.util.Map,org.apache.storm.trident.operation.TridentOperationContext)"><code>Operation.prepare(Map, TridentOperationContext)</code></a> method to perform your custom initialization. |
| |
| <p>### 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 <a href="../state/State.html" title="interface in org.apache.storm.trident.state"><code>State</code></a> or |
| <a href="../state/QueryFunction.html" title="interface in org.apache.storm.trident.state"><code>QueryFunction</code></a> implementation since Trident states operate on batch partitions |
| and can perform bulk updates to a database.</div> |
| </section> |
| <section class="summary"> |
| <ul class="summary-list"> |
| <!-- ========== METHOD SUMMARY =========== --> |
| <li> |
| <section class="method-summary" id="method-summary"> |
| <h2>Method Summary</h2> |
| <div id="method-summary-table"> |
| <div class="table-tabs" role="tablist" aria-orientation="horizontal"><button id="method-summary-table-tab0" role="tab" aria-selected="true" aria-controls="method-summary-table.tabpanel" tabindex="0" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table', 3)" class="active-table-tab">All Methods</button><button id="method-summary-table-tab2" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab2', 3)" class="table-tab">Instance Methods</button><button id="method-summary-table-tab3" role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" onclick="show('method-summary-table', 'method-summary-table-tab3', 3)" class="table-tab">Abstract Methods</button></div> |
| <div id="method-summary-table.tabpanel" role="tabpanel"> |
| <div class="summary-table three-column-summary" aria-labelledby="method-summary-table-tab0"> |
| <div class="table-header col-first">Modifier and Type</div> |
| <div class="table-header col-second">Method</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code>void</code></div> |
| <div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"><code><a href="#execute(org.apache.storm.trident.tuple.TridentTuple,org.apache.storm.trident.operation.TridentCollector)" class="member-name-link">execute</a><wbr>(<a href="../tuple/TridentTuple.html" title="interface in org.apache.storm.trident.tuple">TridentTuple</a> tuple, |
| <a href="TridentCollector.html" title="interface in org.apache.storm.trident.operation">TridentCollector</a> collector)</code></div> |
| <div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab3"> |
| <div class="block">Performs the function logic on an individual tuple and emits 0 or more tuples.</div> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="inherited-list"> |
| <h3 id="methods-inherited-from-class-org.apache.storm.trident.operation.Operation">Methods inherited from interface org.apache.storm.trident.operation.<a href="Operation.html" title="interface in org.apache.storm.trident.operation">Operation</a></h3> |
| <code><a href="Operation.html#cleanup()">cleanup</a>, <a href="Operation.html#prepare(java.util.Map,org.apache.storm.trident.operation.TridentOperationContext)">prepare</a></code></div> |
| </section> |
| </li> |
| </ul> |
| </section> |
| <section class="details"> |
| <ul class="details-list"> |
| <!-- ============ METHOD DETAIL ========== --> |
| <li> |
| <section class="method-details" id="method-detail"> |
| <h2>Method Details</h2> |
| <ul class="member-list"> |
| <li> |
| <section class="detail" id="execute(org.apache.storm.trident.tuple.TridentTuple,org.apache.storm.trident.operation.TridentCollector)"> |
| <h3>execute</h3> |
| <div class="member-signature"><span class="return-type">void</span> <span class="element-name">execute</span><wbr><span class="parameters">(<a href="../tuple/TridentTuple.html" title="interface in org.apache.storm.trident.tuple">TridentTuple</a> tuple, |
| <a href="TridentCollector.html" title="interface in org.apache.storm.trident.operation">TridentCollector</a> collector)</span></div> |
| <div class="block">Performs the function logic on an individual tuple and emits 0 or more tuples.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>tuple</code> - The incoming tuple</dd> |
| <dd><code>collector</code> - A collector instance that can be used to emit tuples</dd> |
| </dl> |
| </section> |
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