Re: [PR] KAFKA-16339: [Docs] Add migrating from transform to process [kafka]

[via GitHub]

mjsax commented on code in PR #18314:
URL: https://github.com/apache/kafka/pull/18314#discussion_r1896961093


##########
docs/streams/developer-guide/dsl-api.html:
##########
@@ -3243,6 +3244,177 @@ <h5><a class="toc-backref" href="#id34">KTable-KTable 
Foreign-Key
          // `Processor` interface, see further down below.
          .process(() -&gt; new 
PopularPageEmailAlert(&quot;ale...@yourcompany.com&quot;));</code></pre>
         </div>
+        <div class="section" id="migrating-from-transform-to-process">
+            <h2>
+                <a class="headerlink" 
href="#migrating-from-transform-to-process" title="Permalink to this headline">
+                    Migrating from transform to process
+                </a>
+            </h2>
+            <div>
+                <p>
+                    As of Kafka 4.0, several deprecated methods in the Kafka 
Streams API, such as <code>transform</code>,
+                    <code>flatTransform</code>, <code>transformValues</code>, 
and <code>flatTransformValues</code>, have
+                    been removed. These methods have been replaced with the 
more versatile <code>process</code> API. This
+                    guide provides detailed steps for migrating existing code 
to use the new <code>process</code> API and
+                    explains the benefits of the changes.
+                </p>
+                <h3>Overview of Changes</h3>
+                <p>The following deprecated methods are no longer available in 
Kafka Streams:</p>
+                <ul>
+                    <li><code>KStream#transform</code></li>
+                    <li><code>KStream#flatTransform</code></li>
+                    <li><code>KStream#transformValues</code></li>
+                    <li><code>KStream#flatTransformValues</code></li>
+                </ul>
+                <p>The <code>process</code> API now serves as a unified 
replacement for all these methods. It simplifies the
+                    API surface while maintaining support for both stateless 
and stateful operations.</p>
+
+                <h3>Migration Steps</h3>
+
+                <h4>1. Migrate from <code>transform</code> to 
<code>process</code></h4>
+
+                <pre class="line-numbers"><code class="language-java">// Before
+KStream&lt;String, String> transformedStream = stream.transform(
+  () -> new CustomTransformer(),
+  "state-store"
+);
+
+// After
+KStream&lt;String, String> processedStream = stream.process(
+  () -> new CustomProcessor(),
+  "state-store"
+);</code></pre>
+
+                <h4>2. Migrate from <code>flatTransform</code> to 
<code>process</code></h4>
+                <pre class="line-numbers"><code class="language-java">// Before
+KStream&lt;String, String> flatTransformedStream = stream.flatTransform(
+  () -> new CustomFlatTransformer(),
+  "state-store"
+);
+
+// After
+KStream&lt;String, String> processedStream = stream.process(
+  () -> new Processor&lt;String, String>() {

Review Comment:
   The new `api.Processor` has 4 generic, key/value in/out.



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