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<h2 title="Interface Transformer" class="title">Interface Transformer&lt;K,V,R&gt;</h2>
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<dl>
<dt><span class="paramLabel">Type Parameters:</span></dt>
<dd><code>K</code> - key type</dd>
<dd><code>V</code> - value type</dd>
<dd><code>R</code> - <a href="../../../../../org/apache/kafka/streams/KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> return type (both key and value type can be set
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<pre>public interface <span class="typeNameLabel">Transformer&lt;K,V,R&gt;</span></pre>
<div class="block">The <code>Transformer</code> interface is for stateful mapping of an input record to zero, one, or multiple new output
records (both key and value type can be altered arbitrarily).
This is a stateful record-by-record operation, i.e, <a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#transform-K-V-"><code>transform(Object, Object)</code></a> is invoked individually for
each record of a stream and can access and modify a state that is available beyond a single call of
<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#transform-K-V-"><code>transform(Object, Object)</code></a> (cf. <a href="../../../../../org/apache/kafka/streams/kstream/KeyValueMapper.html" title="interface in org.apache.kafka.streams.kstream"><code>KeyValueMapper</code></a> for stateless record transformation).
Additionally, this <code>Transformer</code> can <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#schedule-long-org.apache.kafka.streams.processor.PunctuationType-org.apache.kafka.streams.processor.Punctuator-"><code>schedule</code></a>
a method to be <a href="../../../../../org/apache/kafka/streams/processor/Punctuator.html#punctuate-long-"><code>called periodically</code></a> with the provided context.
<p>
Use <a href="../../../../../org/apache/kafka/streams/kstream/TransformerSupplier.html" title="interface in org.apache.kafka.streams.kstream"><code>TransformerSupplier</code></a> to provide new instances of <code>Transformer</code> to Kafka Stream's runtime.
<p>
If only a record's value should be modified <a href="../../../../../org/apache/kafka/streams/kstream/ValueTransformer.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueTransformer</code></a> can be used.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="../../../../../org/apache/kafka/streams/kstream/TransformerSupplier.html" title="interface in org.apache.kafka.streams.kstream"><code>TransformerSupplier</code></a>,
<a href="../../../../../org/apache/kafka/streams/kstream/KStream.html#transform-org.apache.kafka.streams.kstream.TransformerSupplier-java.lang.String...-"><code>KStream.transform(TransformerSupplier, String...)</code></a>,
<a href="../../../../../org/apache/kafka/streams/kstream/ValueTransformer.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueTransformer</code></a>,
<a href="../../../../../org/apache/kafka/streams/kstream/KStream.html#map-org.apache.kafka.streams.kstream.KeyValueMapper-"><code>KStream.map(KeyValueMapper)</code></a>,
<a href="../../../../../org/apache/kafka/streams/kstream/KStream.html#flatMap-org.apache.kafka.streams.kstream.KeyValueMapper-"><code>KStream.flatMap(KeyValueMapper)</code></a></dd>
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<tr>
<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colSecond" scope="col">Method</th>
<th class="colLast" scope="col">Description</th>
</tr>
<tr id="i0" class="altColor">
<td class="colFirst"><code>void</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#close--">close</a></span>&#8203;()</code></th>
<td class="colLast">
<div class="block">Close this processor and clean up any resources.</div>
</td>
</tr>
<tr id="i1" class="rowColor">
<td class="colFirst"><code>void</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#init-org.apache.kafka.streams.processor.ProcessorContext-">init</a></span>&#8203;(<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor">ProcessorContext</a>&nbsp;context)</code></th>
<td class="colLast">
<div class="block">Initialize this transformer.</div>
</td>
</tr>
<tr id="i2" class="altColor">
<td class="colFirst"><code><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">R</a></code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#punctuate-long-">punctuate</a></span>&#8203;(long&nbsp;timestamp)</code></th>
<td class="colLast">
<div class="block"><span class="deprecatedLabel">Deprecated.</span>&nbsp;
<div class="block"><span class="deprecationComment">Please use <a href="../../../../../org/apache/kafka/streams/processor/Punctuator.html" title="interface in org.apache.kafka.streams.processor"><code>Punctuator</code></a> functional interface instead.</span></div>
</div>
</td>
</tr>
<tr id="i3" class="rowColor">
<td class="colFirst"><code><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">R</a></code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#transform-K-V-">transform</a></span>&#8203;(<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">K</a>&nbsp;key,
<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">V</a>&nbsp;value)</code></th>
<td class="colLast">
<div class="block">Transform the record with the given key and value.</div>
</td>
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<h4>init</h4>
<pre>void&nbsp;init&#8203;(<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor">ProcessorContext</a>&nbsp;context)</pre>
<div class="block">Initialize this transformer.
This is called once per instance when the topology gets initialized.
<p>
The provided <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor"><code>context</code></a> can be used to access topology and record meta data, to
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#schedule-long-org.apache.kafka.streams.processor.PunctuationType-org.apache.kafka.streams.processor.Punctuator-"><code>schedule</code></a> a method to be
<a href="../../../../../org/apache/kafka/streams/processor/Punctuator.html#punctuate-long-"><code>called periodically</code></a> and to access attached <a href="../../../../../org/apache/kafka/streams/processor/StateStore.html" title="interface in org.apache.kafka.streams.processor"><code>StateStore</code></a>s.
<p>
Note, that <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor"><code>ProcessorContext</code></a> is updated in the background with the current record's meta data.
Thus, it only contains valid record meta data when accessed within <a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#transform-K-V-"><code>transform(Object, Object)</code></a>.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>context</code> - the context</dd>
</dl>
</li>
</ul>
<a name="transform-java.lang.Object-java.lang.Object-">
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<h4>transform</h4>
<pre><a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">R</a>&nbsp;transform&#8203;(<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">K</a>&nbsp;key,
<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">V</a>&nbsp;value)</pre>
<div class="block">Transform the record with the given key and value.
Additionally, any <a href="../../../../../org/apache/kafka/streams/processor/StateStore.html" title="interface in org.apache.kafka.streams.processor"><code>state</code></a> that is <a href="../../../../../org/apache/kafka/streams/kstream/KStream.html#transform-org.apache.kafka.streams.kstream.TransformerSupplier-java.lang.String...-"><code>attached</code></a> to this operator can be accessed and modified
arbitrarily (cf. <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#getStateStore-java.lang.String-"><code>ProcessorContext.getStateStore(String)</code></a>).
<p>
If more than one output record should be forwarded downstream <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-"><code>ProcessorContext.forward(Object, Object)</code></a>,
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-int-"><code>ProcessorContext.forward(Object, Object, int)</code></a>, and
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-java.lang.String-"><code>ProcessorContext.forward(Object, Object, String)</code></a> can be used.
If not record should be forwarded downstream, <code>transform</code> can return <code>null</code>.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>key</code> - the key for the record</dd>
<dd><code>value</code> - the value for the record</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>new <a href="../../../../../org/apache/kafka/streams/KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pair&mdash;if <code>null</code> no key-value pair will
be forwarded to down stream</dd>
</dl>
</li>
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<a name="punctuate-long-">
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<h4>punctuate</h4>
<pre>@Deprecated
<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html" title="type parameter in Transformer">R</a>&nbsp;punctuate&#8203;(long&nbsp;timestamp)</pre>
<div class="block"><span class="deprecatedLabel">Deprecated.</span>&nbsp;<span class="deprecationComment">Please use <a href="../../../../../org/apache/kafka/streams/processor/Punctuator.html" title="interface in org.apache.kafka.streams.processor"><code>Punctuator</code></a> functional interface instead.</span></div>
<div class="block">Perform any periodic operations and possibly generate new <a href="../../../../../org/apache/kafka/streams/KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pairs if this processor
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#schedule-long-"><code>schedules itself</code></a> with the context during
<a href="../../../../../org/apache/kafka/streams/kstream/Transformer.html#init-org.apache.kafka.streams.processor.ProcessorContext-"><code>initialization</code></a>.
<p>
To generate new <a href="../../../../../org/apache/kafka/streams/KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pairs <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-"><code>ProcessorContext.forward(Object, Object)</code></a>,
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-int-"><code>ProcessorContext.forward(Object, Object, int)</code></a>, and
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-java.lang.String-"><code>ProcessorContext.forward(Object, Object, String)</code></a> can be used.
<p>
Note that <code>punctuate</code> is called based on <it>stream time</it> (i.e., time progresses with regard to
timestamps return by the used <a href="../../../../../org/apache/kafka/streams/processor/TimestampExtractor.html" title="interface in org.apache.kafka.streams.processor"><code>TimestampExtractor</code></a>)
and not based on wall-clock time.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>timestamp</code> - the stream time when <code>punctuate</code> is being called</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>new <a href="../../../../../org/apache/kafka/streams/KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pair to be forwarded to down stream&mdash;if <code>null</code> will not be forwarded</dd>
</dl>
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<h4>close</h4>
<pre>void&nbsp;close&#8203;()</pre>
<div class="block">Close this processor and clean up any resources.
<p>
To generate new <a href="../../../../../org/apache/kafka/streams/KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pairs <a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-"><code>ProcessorContext.forward(Object, Object)</code></a>,
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-int-"><code>ProcessorContext.forward(Object, Object, int)</code></a>, and
<a href="../../../../../org/apache/kafka/streams/processor/ProcessorContext.html#forward-K-V-java.lang.String-"><code>ProcessorContext.forward(Object, Object, String)</code></a> can be used.</div>
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