Add documentation for accessing Headers on Kafka Streams Processor API
Reviewers: Guozhang Wang
</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">
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
