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  <div class="section" id="data-types-and-serialization">
    <span id="streams-developer-guide-serdes"></span><h1 class="docs-title">Data Types and Serialization<a class="headerlink" href="#data-types-and-serialization" title="Permalink to this headline"></a></h1>
    <p>Every Kafka Streams application must provide SerDes (Serializer/Deserializer) for the data types of record keys and record values (e.g. <code class="docutils literal"><span class="pre">java.lang.String</span></code>) to materialize the data when necessary.  Operations that require such SerDes information include: <code class="docutils literal"><span class="pre">stream()</span></code>, <code class="docutils literal"><span class="pre">table()</span></code>, <code class="docutils literal"><span class="pre">to()</span></code>, <code class="docutils literal"><span class="pre">through()</span></code>, <code class="docutils literal"><span class="pre">groupByKey()</span></code>, <code class="docutils literal"><span class="pre">groupBy()</span></code>.</p>
    <p>You can provide SerDes by using either of these methods:</p>
    <ul class="simple">
      <li>By setting default SerDes in the <code class="docutils literal"><span class="pre">java.util.Properties</span></code> config instance.</li>
      <li>By specifying explicit SerDes when calling the appropriate API methods, thus overriding the defaults.</li>
    </ul>

      <p class="topic-title first"><b>Table of Contents</b></p>
      <ul class="simple">
          <li><a class="reference internal" href="#configuring-serdes" id="id1">Configuring SerDes</a></li>
          <li><a class="reference internal" href="#overriding-default-serdes" id="id2">Overriding default SerDes</a></li>
          <li><a class="reference internal" href="#available-serdes" id="id3">Available SerDes</a></li>
          <ul>
              <li><a class="reference internal" href="#primitive-and-basic-types" id="id4">Primitive and basic types</a></li>
              <li><a class="reference internal" href="#json" id="id6">JSON</a></li>
              <li><a class="reference internal" href="#implementing-custom-serdes" id="id5">Implementing custom serdes</a></li>
          </ul>
          <li><a class="reference internal" href="#scala-dsl-serdes" id="id8">Kafka Streams DSL for Scala Implicit SerDes</a></li>
      </ul>
    <div class="section" id="configuring-serdes">
      <h2>Configuring SerDes<a class="headerlink" href="#configuring-serdes" title="Permalink to this headline"></a></h2>
      <p>SerDes specified in the Streams configuration are used as the default in your Kafka Streams application.</p>
      <div class="highlight-java"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">org.apache.kafka.common.serialization.Serdes</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.apache.kafka.streams.StreamsConfig</span><span class="o">;</span>

<span class="n">Properties</span> <span class="n">settings</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Properties</span><span class="o">();</span>
<span class="c1">// Default serde for keys of data records (here: built-in serde for String type)</span>
<span class="n">settings</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">StreamsConfig</span><span class="o">.</span><span class="na">DEFAULT_KEY_SERDE_CLASS_CONFIG</span><span class="o">,</span> <span class="n">Serdes</span><span class="o">.</span><span class="na">String</span><span class="o">().</span><span class="na">getClass</span><span class="o">().</span><span class="na">getName</span><span class="o">());</span>
<span class="c1">// Default serde for values of data records (here: built-in serde for Long type)</span>
<span class="n">settings</span><span class="o">.</span><span class="na">put</span><span class="o">(</span><span class="n">StreamsConfig</span><span class="o">.</span><span class="na">DEFAULT_VALUE_SERDE_CLASS_CONFIG</span><span class="o">,</span> <span class="n">Serdes</span><span class="o">.</span><span class="na">Long</span><span class="o">().</span><span class="na">getClass</span><span class="o">().</span><span class="na">getName</span><span class="o">());</span></pre></div>
      </div>
    </div>
    <div class="section" id="overriding-default-serdes">
      <h2>Overriding default SerDes<a class="headerlink" href="#overriding-default-serdes" title="Permalink to this headline"></a></h2>
      <p>You can also specify SerDes explicitly by passing them to the appropriate API methods, which overrides the default serde settings:</p>
      <div class="highlight-java"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">org.apache.kafka.common.serialization.Serde</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.apache.kafka.common.serialization.Serdes</span><span class="o">;</span>

<span class="kd">final</span> <span class="n">Serde</span><span class="o">&lt;</span><span class="n">String</span><span class="o">&gt;</span> <span class="n">stringSerde</span> <span class="o">=</span> <span class="n">Serdes</span><span class="o">.</span><span class="na">String</span><span class="o">();</span>
<span class="kd">final</span> <span class="n">Serde</span><span class="o">&lt;</span><span class="n">Long</span><span class="o">&gt;</span> <span class="n">longSerde</span> <span class="o">=</span> <span class="n">Serdes</span><span class="o">.</span><span class="na">Long</span><span class="o">();</span>

<span class="c1">// The stream userCountByRegion has type `String` for record keys (for region)</span>
<span class="c1">// and type `Long` for record values (for user counts).</span>
<span class="n">KStream</span><span class="o">&lt;</span><span class="n">String</span><span class="o">,</span> <span class="n">Long</span><span class="o">&gt;</span> <span class="n">userCountByRegion</span> <span class="o">=</span> <span class="o">...;</span>
<span class="n">userCountByRegion</span><span class="o">.</span><span class="na">to</span><span class="o">(</span><span class="s">&quot;RegionCountsTopic&quot;</span><span class="o">,</span> <span class="n">Produced</span><span class="o">.</span><span class="na">with</span><span class="o">(</span><span class="n">stringSerde</span><span class="o">,</span> <span class="n">longSerde</span><span class="o">));</span></pre></div>
      </div>
      <p>If you want to override serdes selectively, i.e., keep the defaults for some fields, then don&#8217;t specify the serde whenever you want to leverage the default settings:</p>
      <div class="highlight-java"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">org.apache.kafka.common.serialization.Serde</span><span class="o">;</span>
<span class="kn">import</span> <span class="nn">org.apache.kafka.common.serialization.Serdes</span><span class="o">;</span>

<span class="c1">// Use the default serializer for record keys (here: region as String) by not specifying the key serde,</span>
<span class="c1">// but override the default serializer for record values (here: userCount as Long).</span>
<span class="kd">final</span> <span class="n">Serde</span><span class="o">&lt;</span><span class="n">Long</span><span class="o">&gt;</span> <span class="n">longSerde</span> <span class="o">=</span> <span class="n">Serdes</span><span class="o">.</span><span class="na">Long</span><span class="o">();</span>
<span class="n">KStream</span><span class="o">&lt;</span><span class="n">String</span><span class="o">,</span> <span class="n">Long</span><span class="o">&gt;</span> <span class="n">userCountByRegion</span> <span class="o">=</span> <span class="o">...;</span>
<span class="n">userCountByRegion</span><span class="o">.</span><span class="na">to</span><span class="o">(</span><span class="s">&quot;RegionCountsTopic&quot;</span><span class="o">,</span> <span class="n">Produced</span><span class="o">.</span><span class="na">valueSerde</span><span class="o">(</span><span class="n">Serdes</span><span class="o">.</span><span class="na">Long</span><span class="o">()));</span></pre></div>
      </div>
      <p>If some of your incoming records are corrupted or ill-formatted, they will cause the deserializer class to report an error.
         Since 1.0.x we have introduced an <code>DeserializationExceptionHandler</code> interface which allows
         you to customize how to handle such records. The customized implementation of the interface can be specified via the <code>StreamsConfig</code>.
         For more details, please feel free to read the <a href="config-streams.html#default-deserialization-exception-handler">Configuring a Streams Application</a> section.
      </p>
    </div>
    <div class="section" id="available-serdes">
      <span id="streams-developer-guide-serdes-available"></span><h2>Available SerDes<a class="headerlink" href="#available-serdes" title="Permalink to this headline"></a></h2>
      <div class="section" id="primitive-and-basic-types">
        <h3>Primitive and basic types<a class="headerlink" href="#primitive-and-basic-types" title="Permalink to this headline"></a></h3>
        <p>Apache Kafka includes several built-in serde implementations for Java primitives and basic types such as <code class="docutils literal"><span class="pre">byte[]</span></code> in
          its <code class="docutils literal"><span class="pre">kafka-clients</span></code> Maven artifact:</p>
        <div class="highlight-xml"><div class="highlight"><pre><span></span><span class="nt">&lt;dependency&gt;</span>
    <span class="nt">&lt;groupId&gt;</span>org.apache.kafka<span class="nt">&lt;/groupId&gt;</span>
    <span class="nt">&lt;artifactId&gt;</span>kafka-clients<span class="nt">&lt;/artifactId&gt;</span>
    <span class="nt">&lt;version&gt;</span>{{fullDotVersion}}<span class="nt">&lt;/version&gt;</span>
<span class="nt">&lt;/dependency&gt;</span></pre></div>
        </div>
        <p>This artifact provides the following serde implementations under the package <a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/clients/src/main/java/org/apache/kafka/common/serialization">org.apache.kafka.common.serialization</a>, which you can leverage when e.g., defining default serializers in your Streams configuration.</p>
        <table border="1" class="docutils">
          <colgroup>
            <col width="17%" />
            <col width="83%" />
          </colgroup>
          <thead valign="bottom">
          <tr class="row-odd"><th class="head">Data type</th>
            <th class="head">Serde</th>
          </tr>
          </thead>
          <tbody valign="top">
          <tr class="row-even"><td>byte[]</td>
            <td><code class="docutils literal"><span class="pre">Serdes.ByteArray()</span></code>, <code class="docutils literal"><span class="pre">Serdes.Bytes()</span></code> (see tip below)</td>
          </tr>
          <tr class="row-odd"><td>ByteBuffer</td>
            <td><code class="docutils literal"><span class="pre">Serdes.ByteBuffer()</span></code></td>
          </tr>
          <tr class="row-even"><td>Double</td>
            <td><code class="docutils literal"><span class="pre">Serdes.Double()</span></code></td>
          </tr>
          <tr class="row-odd"><td>Integer</td>
            <td><code class="docutils literal"><span class="pre">Serdes.Integer()</span></code></td>
          </tr>
          <tr class="row-even"><td>Long</td>
            <td><code class="docutils literal"><span class="pre">Serdes.Long()</span></code></td>
          </tr>
          <tr class="row-odd"><td>String</td>
            <td><code class="docutils literal"><span class="pre">Serdes.String()</span></code></td>
          </tr>
          <tr class="row-even"><td>UUID</td>
            <td><code class="docutils literal"><span class="pre">Serdes.UUID()</span></code></td>
          </tr>
          </tr>
          <tr class="row-odd"><td>Void</td>
              <td><code class="docutils literal"><span class="pre">Serdes.Void()</span></code></td>
          </tr>
          </tbody>
        </table>
        <div class="admonition tip">
          <p><b>Tip</b></p>
          <p class="last"><a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/clients/src/main/java/org/apache/kafka/common/utils/Bytes.java">Bytes</a> is a wrapper for Java&#8217;s <code class="docutils literal"><span class="pre">byte[]</span></code> (byte array) that supports proper equality and ordering semantics.  You may want to consider using <code class="docutils literal"><span class="pre">Bytes</span></code> instead of <code class="docutils literal"><span class="pre">byte[]</span></code> in your applications.</p>
        </div>
      </div>
      <div class="section" id="json">
        <h3>JSON<a class="headerlink" href="#json" title="Permalink to this headline"></a></h3>
        <p>The Kafka Streams code examples also include a basic serde implementation for JSON:</p>
        <ul class="simple">
          <li><a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/streams/examples/src/main/java/org/apache/kafka/streams/examples/pageview/PageViewTypedDemo.java#L83">PageViewTypedDemo</a></li>
        </ul>
        <p>As shown in the example, you can use JSONSerdes inner classes <code class="docutils literal"><span class="pre">Serdes.serdeFrom(&lt;serializerInstance&gt;, &lt;deserializerInstance&gt;)</span></code> to construct JSON compatible serializers and deserializers.
        </p>
      </div>
      <div class="section" id="implementing-custom-serdes">
        <span id="streams-developer-guide-serdes-custom"></span><h2>Implementing custom SerDes<a class="headerlink" href="#implementing-custom-serdes" title="Permalink to this headline"></a></h2>
        <p>If you need to implement custom SerDes, your best starting point is to take a look at the source code references of
          existing SerDes (see previous section).  Typically, your workflow will be similar to:</p>
        <ol class="arabic simple">
          <li>Write a <em>serializer</em> for your data type <code class="docutils literal"><span class="pre">T</span></code> by implementing
            <a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/clients/src/main/java/org/apache/kafka/common/serialization/Serializer.java">org.apache.kafka.common.serialization.Serializer</a>.</li>
          <li>Write a <em>deserializer</em> for <code class="docutils literal"><span class="pre">T</span></code> by implementing
            <a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/clients/src/main/java/org/apache/kafka/common/serialization/Deserializer.java">org.apache.kafka.common.serialization.Deserializer</a>.</li>
          <li>Write a <em>serde</em> for <code class="docutils literal"><span class="pre">T</span></code> by implementing
            <a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/clients/src/main/java/org/apache/kafka/common/serialization/Serde.java">org.apache.kafka.common.serialization.Serde</a>,
            which you either do manually (see existing SerDes in the previous section) or by leveraging helper functions in
            <a class="reference external" href="https://github.com/apache/kafka/blob/{{dotVersion}}/clients/src/main/java/org/apache/kafka/common/serialization/Serdes.java">Serdes</a>
            such as <code class="docutils literal"><span class="pre">Serdes.serdeFrom(Serializer&lt;T&gt;, Deserializer&lt;T&gt;)</span></code>.
            Note that you will need to implement your own class (that has no generic types) if you want to use your custom serde in the configuration provided to <code class="docutils literal"><span class="pre">KafkaStreams</span></code>.
            If your serde class has generic types or you use <code class="docutils literal"><span class="pre">Serdes.serdeFrom(Serializer&lt;T&gt;, Deserializer&lt;T&gt;)</span></code>, you can pass your serde only
            via methods calls (for example <code class="docutils literal"><span class="pre">builder.stream("topicName", Consumed.with(...))</span></code>).</li>
        </ol>
      </div>
    </div>
    <div class="section" id="scala-dsl-serdes">
      <h2>Kafka Streams DSL for Scala Implicit SerDes<a class="headerlink" href="scala-dsl-serdes" title="Permalink to this headline"></a></h2>
      <p>When using the <a href="dsl-api.html#scala-dsl">Kafka Streams DSL for Scala</a> you're not required to configure a default SerDes.  In fact, it's not supported.  SerDes are instead provided implicitly by default implementations for common primitive datatypes.  See the <a href="dsl-api.html#scala-dsl-implicit-serdes">Implicit SerDes</a> and <a href="dsl-api.html#scala-dsl-user-defined-serdes">User-Defined SerDes</a> sections in the DSL API documentation for details</p>
    </div>


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