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| <h2 title="Interface Function" class="title">Interface Function</h2> |
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| <dt>All Superinterfaces:</dt> |
| <dd><a href="../../../../../org/apache/storm/trident/operation/EachOperation.html" title="interface in org.apache.storm.trident.operation">EachOperation</a>, <a href="../../../../../org/apache/storm/trident/operation/Operation.html" title="interface in org.apache.storm.trident.operation">Operation</a>, <a href="http://docs.oracle.com/javase/7/docs/api/java/io/Serializable.html?is-external=true" title="class or interface in java.io">Serializable</a></dd> |
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| <dt>All Known Implementing Classes:</dt> |
| <dd><a href="../../../../../org/apache/storm/trident/operation/BaseFunction.html" title="class in org.apache.storm.trident.operation">BaseFunction</a>, <a href="../../../../../org/apache/storm/trident/operation/impl/CombinerAggregatorInitImpl.html" title="class in org.apache.storm.trident.operation.impl">CombinerAggregatorInitImpl</a>, <a href="../../../../../org/apache/storm/trident/operation/impl/ConsumerExecutor.html" title="class in org.apache.storm.trident.operation.impl">ConsumerExecutor</a>, <a href="../../../../../org/apache/storm/trident/operation/impl/FilterExecutor.html" title="class in org.apache.storm.trident.operation.impl">FilterExecutor</a>, <a href="../../../../../org/apache/storm/trident/operation/impl/FlatMapFunctionExecutor.html" title="class in org.apache.storm.trident.operation.impl">FlatMapFunctionExecutor</a>, <a href="../../../../../org/apache/storm/sql/runtime/trident/functions/ForwardFunction.html" title="class in org.apache.storm.sql.runtime.trident.functions">ForwardFunction</a>, <a href="../../../../../org/apache/storm/trident/operation/impl/MapFunctionExecutor.html" title="class in org.apache.storm.trident.operation.impl">MapFunctionExecutor</a>, <a href="../../../../../org/apache/storm/mqtt/trident/MqttPublishFunction.html" title="class in org.apache.storm.mqtt.trident">MqttPublishFunction</a>, <a href="../../../../../org/apache/storm/redis/trident/PrintFunction.html" title="class in org.apache.storm.redis.trident">PrintFunction</a>, <a href="../../../../../org/apache/storm/hbase/trident/PrintFunction.html" title="class in org.apache.storm.hbase.trident">PrintFunction</a>, <a href="../../../../../org/apache/storm/trident/testing/Split.html" title="class in org.apache.storm.trident.testing">Split</a>, <a href="../../../../../org/apache/storm/trident/testing/StringLength.html" title="class in org.apache.storm.trident.testing">StringLength</a>, <a href="../../../../../org/apache/storm/starter/trident/TridentReach.ExpandList.html" title="class in org.apache.storm.starter.trident">TridentReach.ExpandList</a>, <a href="../../../../../org/apache/storm/starter/trident/TridentWordCount.Split.html" title="class in org.apache.storm.starter.trident">TridentWordCount.Split</a>, <a href="../../../../../org/apache/storm/trident/testing/TuplifyArgs.html" title="class in org.apache.storm.trident.testing">TuplifyArgs</a></dd> |
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| <pre>public interface <span class="typeNameLabel">Function</span> |
| extends <a href="../../../../../org/apache/storm/trident/operation/EachOperation.html" title="interface in org.apache.storm.trident.operation">EachOperation</a></pre> |
| <div class="block"><p>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><p>For example, if you have the following function:</p> |
| <pre><code class="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)); |
| } |
| } |
| } |
| |
| </code></pre><p>Now suppose you have a stream in the variable <code>mystream</code> with the fields <code>["a", "b", "c"]</code> with the following tuples:</p> |
| <pre><code class="no-highlight">[1, 2, 3] |
| [4, 1, 6] |
| [3, 0, 8] |
| </code></pre><p>If you had the following code in your topology definition:</p> |
| <pre><code class="java">mystream.each(new Fields("b"), new MyFunction(), new Fields("d"))) |
| </code></pre><p>The resulting tuples would have the fields <code>["a", "b", "c", "d"]</code> and look like this:</p> |
| <pre><code class="no-highlight">[1, 2, 3, 0] |
| [1, 2, 3, 1] |
| [4, 1, 6, 0] |
| </code></pre><p>In this case, the parameter <code>new Fields("b")</code> 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 <code>execute()</code> 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 <code>for</code> loop to be skipped, so nothing is emitted and the incoming tuple is filtered out of the stream.</p><h3>Configuration</h3><p>If your <code>Function</code> implementation has configuration requirements, you will typically want to extend <a href="../../../../../org/apache/storm/trident/operation/BaseFunction.html" title="class in org.apache.storm.trident.operation"><code>BaseFunction</code></a> and override the <a href="../../../../../org/apache/storm/trident/operation/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><h3>Performance Considerations</h3><p>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="../../../../../org/apache/storm/trident/state/State.html" title="interface in org.apache.storm.trident.state"><code>State</code></a> or <a href="../../../../../org/apache/storm/trident/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.</p></div> |
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| <h3>Method Summary</h3> |
| <table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation"> |
| <caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd"> </span></span><span id="t3" class="tableTab"><span><a href="javascript:show(4);">Abstract Methods</a></span><span class="tabEnd"> </span></span></caption> |
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| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/storm/trident/operation/Function.html#execute-org.apache.storm.trident.tuple.TridentTuple-org.apache.storm.trident.operation.TridentCollector-">execute</a></span>(<a href="../../../../../org/apache/storm/trident/tuple/TridentTuple.html" title="interface in org.apache.storm.trident.tuple">TridentTuple</a> tuple, |
| <a href="../../../../../org/apache/storm/trident/operation/TridentCollector.html" title="interface in org.apache.storm.trident.operation">TridentCollector</a> collector)</code> |
| <div class="block">Performs the function logic on an individual tuple and emits 0 or more tuples.</div> |
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| <h3>Methods inherited from interface org.apache.storm.trident.operation.<a href="../../../../../org/apache/storm/trident/operation/Operation.html" title="interface in org.apache.storm.trident.operation">Operation</a></h3> |
| <code><a href="../../../../../org/apache/storm/trident/operation/Operation.html#cleanup--">cleanup</a>, <a href="../../../../../org/apache/storm/trident/operation/Operation.html#prepare-java.util.Map-org.apache.storm.trident.operation.TridentOperationContext-">prepare</a></code></li> |
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| <h4>execute</h4> |
| <pre>void execute(<a href="../../../../../org/apache/storm/trident/tuple/TridentTuple.html" title="interface in org.apache.storm.trident.tuple">TridentTuple</a> tuple, |
| <a href="../../../../../org/apache/storm/trident/operation/TridentCollector.html" title="interface in org.apache.storm.trident.operation">TridentCollector</a> collector)</pre> |
| <div class="block"><p>Performs the function logic on an individual tuple and emits 0 or more tuples.</p></div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>tuple</code> - The incoming tuple</dd> |
| <dd><code>collector</code> - A collector instance that can be used to emit tuples</dd> |
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