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| <h1 class="post-title" itemprop="name headline">Asynchronous Client Creation in Ditto Java Client 1.3.0</h1> |
| <p class="post-meta">Published by <img src="https://www.gravatar.com/avatar/d923944b6a8c76e411ff838fb19acfa7?s=135" alt="A photo of Yufei Cai" style="width:50px;border-radius:50%;display:inline-block;margin-right:5px;" /><span itemprop="author" itemscope itemtype="http://schema.org/Person"><span itemprop="name"><a href="https://github.com/yufei-cai" target="_blank">Yufei Cai</a> </span></span> on <time datetime="2020-10-08T00:00:00+00:00" itemprop="datePublished">Oct 8, 2020</time> - Tags: |
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| <p>Before <a href="https://github.com/eclipse/ditto-clients/tree/master/java">Ditto Java Client</a> 1.3.0, |
| a client object connects to a configured Ditto back-end during its creation.</p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">// create a client object and block until it connects to the Ditto back-end.</span> |
| <span class="kd">final</span> <span class="n">DittoClient</span> <span class="n">client</span> <span class="o">=</span> <span class="n">DittoClients</span><span class="o">.</span><span class="na">newInstance</span><span class="o">(</span><span class="n">messagingProvider</span><span class="o">);</span> |
| </code></pre></div></div> |
| |
| <p>There are several problems with the approach.</p> |
| <ol> |
| <li>The calling thread blocks waiting for IO, namely the authentication process |
| and establishment of a websocket.</li> |
| <li>If the client is configured to reconnect, then an incorrect end-ponit configuration |
| makes the factory method block forever.</li> |
| <li>If the client is not configured to reconnect, then the factory method will throw |
| an exception. But it is not possible to give the client reference to the exception |
| handler, since the client creation did not complete. Consequently the exception handler |
| has no simple way to free all resources allocated for the client.</li> |
| </ol> |
| |
| <p>1.3.0 addresses these problems by introducing an asynchronous client creation interface.</p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">public</span> <span class="kd">final</span> <span class="kd">class</span> <span class="nc">DittoClients</span> <span class="o">{</span> |
| |
| <span class="kd">public</span> <span class="kd">static</span> <span class="n">DisconnectedDittoClient</span> <span class="nf">newDisconnectedInstance</span><span class="o">(</span><span class="n">MessagingProvider</span> <span class="n">mp</span><span class="o">);</span> |
| <span class="o">}</span> |
| |
| <span class="kd">public</span> <span class="kd">interface</span> <span class="nc">DisconnectedDittoClient</span> <span class="o">{</span> |
| |
| <span class="n">CompletionStage</span><span class="o"><</span><span class="n">DittoClient</span><span class="o">></span> <span class="nf">connect</span><span class="o">();</span> |
| |
| <span class="kt">void</span> <span class="nf">destroy</span><span class="o">();</span> |
| <span class="o">}</span> |
| </code></pre></div></div> |
| |
| <p>The method <code class="highlighter-rouge">DittoClients.newDisconnectedInstance(MessagingProvider)</code> creates a <code class="highlighter-rouge">DisconnectedDittoClient</code> |
| object. The <code class="highlighter-rouge">DisconnectedDittoClient</code> has references to all resources allocated for the client and |
| can free them via the <code class="highlighter-rouge">destroy()</code> method. The <code class="highlighter-rouge">DisconnectedDittoClient</code> object offers no method to |
| interact with the Ditto API. By calling <code class="highlighter-rouge">connect()</code>, one obtains a future that yields a familiar |
| <code class="highlighter-rouge">DittoClient</code> object upon completion. One might use the asynchronous client creation interface thus:</p> |
| |
| <div class="language-java highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kd">final</span> <span class="n">DisconnectedDittoClient</span> <span class="n">disconnectedClient</span> <span class="o">=</span> |
| <span class="n">DittoClients</span><span class="o">.</span><span class="na">newDisconnectedInstance</span><span class="o">(</span><span class="n">messagingProvider</span><span class="o">);</span> |
| |
| <span class="n">disconnectedClient</span><span class="o">.</span><span class="na">connect</span><span class="o">()</span> |
| <span class="o">.</span><span class="na">thenAccept</span><span class="o">(</span><span class="k">this</span><span class="o">::</span><span class="n">startUsingDittoClient</span><span class="o">)</span> |
| <span class="o">.</span><span class="na">exceptionally</span><span class="o">(</span><span class="n">exception</span> <span class="o">-></span> <span class="o">{</span> |
| <span class="k">this</span><span class="o">.</span><span class="na">handleConnectionFailure</span><span class="o">(</span><span class="n">exception</span><span class="o">);</span> |
| <span class="n">disconnectedClient</span><span class="o">.</span><span class="na">destroy</span><span class="o">();</span> |
| <span class="k">return</span> <span class="kc">null</span><span class="o">;</span> |
| <span class="o">});</span> |
| </code></pre></div></div> |
| |
| <p>The asynchronous client creation interface has the following advantages.</p> |
| |
| <ol> |
| <li> |
| <p>The calling thread does not block.</p> |
| </li> |
| <li> |
| <p>Even if configured to reconnect, the user can receive connection errors via |
| the connection error handler in <code class="highlighter-rouge">MessagingConfiguration</code> and shut down the client |
| at will.</p> |
| </li> |
| <li> |
| <p>When initial reconnection is disabled, the method <code class="highlighter-rouge">DisconnectedDittoClient.connect()</code> |
| returns a failed future on connection error. It is possible to reference the |
| <code class="highlighter-rouge">DittoDisconnectedClient</code> object in the future’s error handler, where the client can |
| be destroyed.</p> |
| </li> |
| </ol> |
| |
| <p><br /> |
| <br /></p> |
| <figure><img class="docimage" src="images/ditto.svg" alt="Ditto" style="max-width: 500px" /></figure> |
| |
| <p>–<br /> |
| The Eclipse Ditto team</p> |
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