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<h1 id="develop-example-http--page-root">Example HTTP Connector<a class="headerlink" href="#develop-example-http--page-root" title="Permalink to this headline">#</a></h1>
<p>The Example HTTP connector has a simple goal: it reads comma-separated
data over HTTP. For example, if you have a large amount of data in a
CSV format, you can point the example HTTP connector at this data and
write a SQL query to process it.</p>

<h2 id="code">Code<a class="headerlink" href="#code" title="Permalink to this headline">#</a></h2>
<p>The Example HTTP connector can be found in the <code class="docutils literal notranslate"><span class="pre">presto-example-http</span></code>
directory in the root of the Presto source tree.</p>


<h2 id="plugin-implementation">Plugin Implementation<a class="headerlink" href="#plugin-implementation" title="Permalink to this headline">#</a></h2>
<p>The plugin implementation in the Example HTTP connector looks very
similar to other plugin implementations.  Most of the implementation is
devoted to handling optional configuration and the only function of
interest is the following:</p>
<div class="highlight-java notranslate"><div class="highlight"><pre><span></span><span class="nd">@Override</span>
<span class="kd">public</span> <span class="n">Iterable</span><span class="o">&lt;</span><span class="n">ConnectorFactory</span><span class="o">&gt;</span> <span class="nf">getConnectorFactories</span><span class="p">()</span>
<span class="p">{</span>
    <span class="k">return</span> <span class="n">ImmutableList</span><span class="p">.</span><span class="na">of</span><span class="p">(</span><span class="k">new</span> <span class="n">ExampleConnectorFactory</span><span class="p">());</span>
<span class="p">}</span>
</pre></div>
</div>
<p>Note that the <code class="docutils literal notranslate"><span class="pre">ImmutableList</span></code> class is a utility class from Guava.</p>
<p>As with all connectors, this plugin overrides the <code class="docutils literal notranslate"><span class="pre">getConnectorFactories()</span></code> method
and returns an <code class="docutils literal notranslate"><span class="pre">ExampleConnectorFactory</span></code>.</p>


<h2 id="connectorfactory-implementation">ConnectorFactory Implementation<a class="headerlink" href="#connectorfactory-implementation" title="Permalink to this headline">#</a></h2>
<p>In Presto, the primary object that handles the connection between
Presto and a particular type of data source is the <code class="docutils literal notranslate"><span class="pre">Connector</span></code> object,
which are created using <code class="docutils literal notranslate"><span class="pre">ConnectorFactory</span></code>.</p>
<p>This implementation is available in the class <code class="docutils literal notranslate"><span class="pre">ExampleConnectorFactory</span></code>.
The first thing the connector factory implementation does is specify the
name of this connector. This is the same string used to reference this
connector in Presto configuration.</p>
<div class="highlight-java notranslate"><div class="highlight"><pre><span></span><span class="nd">@Override</span>
<span class="kd">public</span> <span class="n">String</span> <span class="nf">getName</span><span class="p">()</span>
<span class="p">{</span>
    <span class="k">return</span> <span class="s">"example-http"</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<p>The real work in a connector factory happens in the <code class="docutils literal notranslate"><span class="pre">create()</span></code>
method. In the <code class="docutils literal notranslate"><span class="pre">ExampleConnectorFactory</span></code> class, the <code class="docutils literal notranslate"><span class="pre">create()</span></code> method
configures the connector and then asks Guice to create the object.
This is the meat of the <code class="docutils literal notranslate"><span class="pre">create()</span></code> method without parameter validation
and exception handling:</p>
<div class="highlight-java notranslate"><div class="highlight"><pre><span></span><span class="c1">// A plugin is not required to use Guice; it is just very convenient</span>
<span class="n">Bootstrap</span> <span class="n">app</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Bootstrap</span><span class="p">(</span>
        <span class="k">new</span> <span class="n">JsonModule</span><span class="p">(),</span>
        <span class="k">new</span> <span class="n">ExampleModule</span><span class="p">(</span><span class="n">catalogName</span><span class="p">));</span>

<span class="n">Injector</span> <span class="n">injector</span> <span class="o">=</span> <span class="n">app</span>
        <span class="p">.</span><span class="na">strictConfig</span><span class="p">()</span>
        <span class="p">.</span><span class="na">doNotInitializeLogging</span><span class="p">()</span>
        <span class="p">.</span><span class="na">setRequiredConfigurationProperties</span><span class="p">(</span><span class="n">requiredConfig</span><span class="p">)</span>
        <span class="p">.</span><span class="na">initialize</span><span class="p">();</span>

<span class="k">return</span> <span class="n">injector</span><span class="p">.</span><span class="na">getInstance</span><span class="p">(</span><span class="n">ExampleConnector</span><span class="p">.</span><span class="na">class</span><span class="p">);</span>
</pre></div>
</div>

<h3 id="connector-exampleconnector">Connector: ExampleConnector<a class="headerlink" href="#connector-exampleconnector" title="Permalink to this headline">#</a></h3>
<p>This class allows Presto to obtain references to the various services
provided by the connector.</p>


<h3 id="metadata-examplemetadata">Metadata: ExampleMetadata<a class="headerlink" href="#metadata-examplemetadata" title="Permalink to this headline">#</a></h3>
<p>This class is responsible for reporting table names, table metadata,
column names, column metadata and other information about the schemas
that are provided by this connector. <code class="docutils literal notranslate"><span class="pre">ConnectorMetadata</span></code> is also called
by Presto to ensure that a particular connector can understand and
handle a given table name.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">ExampleMetadata</span></code> implementation delegates many of these calls to
<code class="docutils literal notranslate"><span class="pre">ExampleClient</span></code>, a class that implements much of the core functionality
of the connector.</p>


<h3 id="split-manager-examplesplitmanager">Split Manager: ExampleSplitManager<a class="headerlink" href="#split-manager-examplesplitmanager" title="Permalink to this headline">#</a></h3>
<p>The split manager partitions the data for a table into the individual
chunks that Presto will distribute to workers for processing.
In the case of the Example HTTP connector, each table contains one or
more URIs pointing at the actual data. One split is created per URI.</p>


<h3 id="record-set-provider-examplerecordsetprovider">Record Set Provider: ExampleRecordSetProvider<a class="headerlink" href="#record-set-provider-examplerecordsetprovider" title="Permalink to this headline">#</a></h3>
<p>The record set provider creates a record set which in turn creates a
record cursor that returns the actual data to Presto.
<code class="docutils literal notranslate"><span class="pre">ExampleRecordCursor</span></code> reads data from a URI via HTTP. Each line
corresponds to a single row. Lines are split on comma into individual
field values which are then returned to Presto.</p>


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