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| <div class="sub-title"><span class="package-label-in-type">Package</span> <a href="package-summary.html">org.apache.kafka.streams.kstream</a></div> |
| <h1 title="Interface ValueTransformerWithKey" class="title">Interface ValueTransformerWithKey<K,​V,​VR></h1> |
| </div> |
| <section class="description"> |
| <dl class="notes"> |
| <dt>Type Parameters:</dt> |
| <dd><code>K</code> - key type</dd> |
| <dd><code>V</code> - value type</dd> |
| <dd><code>VR</code> - transformed value type</dd> |
| </dl> |
| <hr> |
| <pre>public interface <span class="type-name-label">ValueTransformerWithKey<K,​V,​VR></span></pre> |
| <div class="block">The <code>ValueTransformerWithKey</code> interface for stateful mapping of a value to a new value (with possible new type). |
| This is a stateful record-by-record operation, i.e, <a href="#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="#transform(K,V)"><code>transform(Object, Object)</code></a> (cf. <a href="ValueMapper.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueMapper</code></a> for stateless value transformation). |
| Additionally, this <code>ValueTransformerWithKey</code> can |
| <a href="../processor/ProcessorContext.html#schedule(java.time.Duration,org.apache.kafka.streams.processor.PunctuationType,org.apache.kafka.streams.processor.Punctuator)"><code>schedule</code></a> a method to be |
| <a href="../processor/Punctuator.html#punctuate(long)"><code>called periodically</code></a> with the provided context. |
| Note that the key is read-only and should not be modified, as this can lead to corrupt partitioning. |
| If <code>ValueTransformerWithKey</code> is applied to a <a href="../KeyValue.html" title="class in org.apache.kafka.streams"><code>KeyValue</code></a> pair record the record's key is preserved. |
| <p> |
| Use <a href="ValueTransformerWithKeySupplier.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueTransformerWithKeySupplier</code></a> to provide new instances of <a href="ValueTransformerWithKey.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueTransformerWithKey</code></a> to |
| Kafka Stream's runtime. |
| <p> |
| If a record's key and value should be modified <a href="Transformer.html" title="interface in org.apache.kafka.streams.kstream"><code>Transformer</code></a> can be used.</div> |
| <dl class="notes"> |
| <dt>See Also:</dt> |
| <dd><a href="ValueTransformer.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueTransformer</code></a>, |
| <a href="ValueTransformerWithKeySupplier.html" title="interface in org.apache.kafka.streams.kstream"><code>ValueTransformerWithKeySupplier</code></a>, |
| <a href="KStream.html#transformValues(org.apache.kafka.streams.kstream.ValueTransformerSupplier,java.lang.String...)"><code>KStream.transformValues(ValueTransformerSupplier, String...)</code></a>, |
| <a href="KStream.html#transformValues(org.apache.kafka.streams.kstream.ValueTransformerWithKeySupplier,java.lang.String...)"><code>KStream.transformValues(ValueTransformerWithKeySupplier, String...)</code></a>, |
| <a href="Transformer.html" title="interface in org.apache.kafka.streams.kstream"><code>Transformer</code></a></dd> |
| </dl> |
| </section> |
| <section class="summary"> |
| <ul class="summary-list"> |
| <!-- ========== METHOD SUMMARY =========== --> |
| <li> |
| <section class="method-summary" id="method.summary"> |
| <h2>Method Summary</h2> |
| <div class="member-summary" id="method-summary-table"> |
| <div class="table-tabs" role="tablist" aria-orientation="horizontal"><button role="tab" aria-selected="true" aria-controls="method-summary-table.tabpanel" tabindex="0" onkeydown="switchTab(event)" id="t0" class="active-table-tab">All Methods</button><button role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" id="t2" class="table-tab" onclick="show(2);">Instance Methods</button><button role="tab" aria-selected="false" aria-controls="method-summary-table.tabpanel" tabindex="-1" onkeydown="switchTab(event)" id="t3" class="table-tab" onclick="show(4);">Abstract Methods</button></div> |
| <div id="method-summary-table.tabpanel" role="tabpanel"> |
| <table class="summary-table" aria-labelledby="t0"> |
| <thead> |
| <tr> |
| <th class="col-first" scope="col">Modifier and Type</th> |
| <th class="col-second" scope="col">Method</th> |
| <th class="col-last" scope="col">Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="alt-color" id="i0"> |
| <td class="col-first"><code>void</code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#close()">close</a></span>()</code></th> |
| <td class="col-last"> |
| <div class="block">Close this processor and clean up any resources.</div> |
| </td> |
| </tr> |
| <tr class="row-color" id="i1"> |
| <td class="col-first"><code>void</code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#init(org.apache.kafka.streams.processor.ProcessorContext)">init</a></span>​(<a href="../processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor">ProcessorContext</a> context)</code></th> |
| <td class="col-last"> |
| <div class="block">Initialize this transformer.</div> |
| </td> |
| </tr> |
| <tr class="alt-color" id="i2"> |
| <td class="col-first"><code><a href="ValueTransformerWithKey.html" title="type parameter in ValueTransformerWithKey">VR</a></code></td> |
| <th class="col-second" scope="row"><code><span class="member-name-link"><a href="#transform(K,V)">transform</a></span>​(<a href="ValueTransformerWithKey.html" title="type parameter in ValueTransformerWithKey">K</a> readOnlyKey, |
| <a href="ValueTransformerWithKey.html" title="type parameter in ValueTransformerWithKey">V</a> value)</code></th> |
| <td class="col-last"> |
| <div class="block">Transform the given [key and] value to a new value.</div> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </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="init(org.apache.kafka.streams.processor.ProcessorContext)"> |
| <h3>init</h3> |
| <div class="member-signature"><span class="return-type">void</span> <span class="member-name">init</span>​(<span class="parameters"><a href="../processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor">ProcessorContext</a> context)</span></div> |
| <div class="block">Initialize this transformer. |
| This is called once per instance when the topology gets initialized. |
| <p> |
| The provided <a href="../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="../processor/ProcessorContext.html#schedule(java.time.Duration,org.apache.kafka.streams.processor.PunctuationType,org.apache.kafka.streams.processor.Punctuator)"><code>schedule</code></a> a method to be |
| <a href="../processor/Punctuator.html#punctuate(long)"><code>called periodically</code></a> and to access attached <a href="../processor/StateStore.html" title="interface in org.apache.kafka.streams.processor"><code>StateStore</code></a>s. |
| <p> |
| Note that <a href="../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="#transform(K,V)"><code>transform(Object, Object)</code></a>. |
| <p> |
| Note that using <a href="../processor/ProcessorContext.html#forward(K,V)"><code>ProcessorContext.forward(Object, Object)</code></a> or |
| <a href="../processor/ProcessorContext.html#forward(K,V,org.apache.kafka.streams.processor.To)"><code>ProcessorContext.forward(Object, Object, To)</code></a> is not allowed within any method of |
| <code>ValueTransformerWithKey</code> and will result in an <a href="../errors/StreamsException.html" title="class in org.apache.kafka.streams.errors"><code>exception</code></a>.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>context</code> - the context</dd> |
| <dt>Throws:</dt> |
| <dd><code><a href="https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/IllegalStateException.html" title="class or interface in java.lang" class="external-link">IllegalStateException</a></code> - If store gets registered after initialization is already finished</dd> |
| <dd><code><a href="../errors/StreamsException.html" title="class in org.apache.kafka.streams.errors">StreamsException</a></code> - if the store's change log does not contain the partition</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="transform(K,V)"> |
| <h3 id="transform(java.lang.Object,java.lang.Object)">transform</h3> |
| <div class="member-signature"><span class="return-type"><a href="ValueTransformerWithKey.html" title="type parameter in ValueTransformerWithKey">VR</a></span> <span class="member-name">transform</span>​(<span class="parameters"><a href="ValueTransformerWithKey.html" title="type parameter in ValueTransformerWithKey">K</a> readOnlyKey, |
| <a href="ValueTransformerWithKey.html" title="type parameter in ValueTransformerWithKey">V</a> value)</span></div> |
| <div class="block">Transform the given [key and] value to a new value. |
| Additionally, any <a href="../processor/StateStore.html" title="interface in org.apache.kafka.streams.processor"><code>StateStore</code></a> that is <a href="KStream.html#transformValues(org.apache.kafka.streams.kstream.ValueTransformerWithKeySupplier,java.lang.String...)"><code>attached</code></a> to this operator can be accessed and modified arbitrarily (cf. |
| <a href="../processor/ProcessorContext.html#getStateStore(java.lang.String)"><code>ProcessorContext.getStateStore(String)</code></a>). |
| <p> |
| Note that using <a href="../processor/ProcessorContext.html#forward(K,V)"><code>ProcessorContext.forward(Object, Object)</code></a> or |
| <a href="../processor/ProcessorContext.html#forward(K,V,org.apache.kafka.streams.processor.To)"><code>ProcessorContext.forward(Object, Object, To)</code></a> is not allowed within <code>transform</code> and |
| will result in an <a href="../errors/StreamsException.html" title="class in org.apache.kafka.streams.errors"><code>exception</code></a>. |
| <p> |
| Note that if a <code>ValueTransformerWithKey</code> is used in a <a href="KTable.html#transformValues(org.apache.kafka.streams.kstream.ValueTransformerWithKeySupplier,java.lang.String...)"><code>KTable.transformValues(ValueTransformerWithKeySupplier, String...)</code></a> |
| (or any other overload of <code>KTable#transformValues(...)</code>) operation, |
| then the provided <a href="../processor/ProcessorContext.html" title="interface in org.apache.kafka.streams.processor"><code>ProcessorContext</code></a> from <a href="#init(org.apache.kafka.streams.processor.ProcessorContext)"><code>init(ProcessorContext)</code></a> |
| does not guarantee that all context information will be available when <code>transform()</code> |
| is executed, as it might be executed "out-of-band" due to some internal optimizations |
| applied by the Kafka Streams DSL.</div> |
| <dl class="notes"> |
| <dt>Parameters:</dt> |
| <dd><code>readOnlyKey</code> - the read-only key</dd> |
| <dd><code>value</code> - the value to be transformed</dd> |
| <dt>Returns:</dt> |
| <dd>the new value</dd> |
| </dl> |
| </section> |
| </li> |
| <li> |
| <section class="detail" id="close()"> |
| <h3>close</h3> |
| <div class="member-signature"><span class="return-type">void</span> <span class="member-name">close</span>()</div> |
| <div class="block">Close this processor and clean up any resources. |
| <p> |
| It is not possible to return any new output records within <code>close()</code>. |
| Using <a href="../processor/ProcessorContext.html#forward(K,V)"><code>ProcessorContext.forward(Object, Object)</code></a> or <a href="../processor/ProcessorContext.html#forward(K,V,org.apache.kafka.streams.processor.To)"><code>ProcessorContext.forward(Object, Object, To)</code></a>, |
| will result in an <a href="../errors/StreamsException.html" title="class in org.apache.kafka.streams.errors"><code>exception</code></a>.</div> |
| </section> |
| </li> |
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