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KAFKA-6938: Add documentation for accessing Headers on Kafka Streams Processor API (#5128) 

Reviewers: Guozhang Wang <wangguoz@gmail.com>
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Jorge Quilcate Otoya 2018-06-05 00:39:20 +02:00 committed by Guozhang Wang
parent 6f9f365573
commit e8ddb76573
1 changed files with 19 additions and 2 deletions
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21
docs/streams/developer-guide/processor-api.html
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@ -53,6 +53,7 @@
</ul>
</li>
<li><a class="reference internal" href="#connecting-processors-and-state-stores" id="id8">Connecting Processors and State Stores</a></li>
<li><a class="reference internal" href="#accessing-processor-context" id="id10">Accessing Processor Context</a></li>
</ul>
</div>
<div class="section" id="overview">
@ -351,6 +352,22 @@
your store.</p>
</div>
</div>
<div class="section" id="accessing-processor-context">
<h2><a class="toc-backref" href="#id10">Accessing Processor Context</a><a class="headerlink" href="#accessing-processor-context" title="Permalink to this headline"></a></h2>
<p>As we have mentioned in <href=#defining-a-stream-processor>Defining a Stream Processor<\href>, a <code>ProcessorContext</code> control the processing workflow, such as scheduling a punctuation function, and committing the current processed state.</p>
<p>This object can also be used to access the metadata related with the application like
<code class="docutils literal"><span class="pre">applicationId</span></code>, <code class="docutils literal"><span class="pre">taskId</span></code>,
and <code class="docutils literal"><span class="pre">stateDir</span></code>, and also record related metadata as <code class="docutils literal"><span class="pre">topic</span></code>,
<code class="docutils literal"><span class="pre">partition</span></code>, <code class="docutils literal"><span class="pre">offset</span></code>, <code class="docutils literal"><span class="pre">timestamp</span></code> and
<code class="docutils literal"><span class="pre">headers</span></code>.</p>
<p>Here is an example implementation of how to add a new header to the record:</p>
<div class="highlight-java"><div class="highlight"><pre><span></span><span class="n">public void process(String key, String value) {</span>
<span class="c1">// add a heaeder to the elements</span>
<span class="n">context()</span><span class="o">.</span><span class="na">headers</span><span class="o">()</span><span class="o">.</span><span class="na">add</span><span class="o">.</span><span class="o">(</span><span class="s">&quot;key&quot;</span><span class="o">,</span> <span class="s">&quot;key&quot;</span>
<span class="o">}</span>
</pre></div>
</div>
<div class="section" id="connecting-processors-and-state-stores">
<h2><a class="toc-backref" href="#id8">Connecting Processors and State Stores</a><a class="headerlink" href="#connecting-processors-and-state-stores" title="Permalink to this headline"></a></h2>
<p>Now that a <a class="reference internal" href="#streams-developer-guide-stream-processor"><span class="std std-ref">processor</span></a> (WordCountProcessor) and the
@ -399,8 +416,8 @@
runtime, indicating the state store is not accessible from this processor.</p>
<p>Now that you have fully defined your processor topology in your application, you can proceed to
<a class="reference internal" href="running-app.html#streams-developer-guide-execution"><span class="std std-ref">running the Kafka Streams application</span></a>.</p>
</div>
</div>
</div>
</div>
</div>