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Oleg Zhurakousky
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<title>6. Programming Model</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="multi_spring-cloud-stream.html" title="Spring Cloud Stream Reference Guide"><link rel="up" href="multi__reference_guide.html" title="Part II. Reference Guide"><link rel="prev" href="multi__main_concepts.html" title="5. Main Concepts"><link rel="next" href="multi_spring-cloud-stream-overview-binders.html" title="7. Binders"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">6. Programming Model</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__main_concepts.html">Prev</a> </td><th width="60%" align="center">Part II. Reference Guide</th><td width="20%" align="right"> <a accesskey="n" href="multi_spring-cloud-stream-overview-binders.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_programming_model" href="#_programming_model"></a>6. Programming Model</h2></div></div></div><p>To understand the programming model, you should be familiar with the following core concepts:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="strong"><strong>Destination Binders:</strong></span> Components responsible to provide integration with the external messaging systems.</li><li class="listitem"><span class="strong"><strong>Destination Bindings:</strong></span> Bridge between the external messaging systems and application provided <span class="emphasis"><em>Producers</em></span> and <span class="emphasis"><em>Consumers</em></span> of messages (created by the Destination Binders).</li><li class="listitem"><span class="strong"><strong>Message:</strong></span> The canonical data structure used by producers and consumers to communicate with Destination Binders (and thus other applications via external messaging systems).</li></ul></div><div class="informalfigure"><div class="mediaobject" align="center"><img src="https://raw.githubusercontent.com/spring-cloud/spring-cloud-stream/master/docs/src/main/asciidoc/images/SCSt-overview.png" align="middle" alt="SCSt overview"></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_destination_binders" href="#_destination_binders"></a>6.1 Destination Binders</h2></div></div></div><p>Destination Binders are extension components of Spring Cloud Stream responsible for providing the necessary configuration and implementation to facilitate
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<title>6. Programming Model</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="multi_spring-cloud-stream.html" title="Spring Cloud Stream Reference Guide"><link rel="up" href="multi__preface.html" title="Part I. Preface"><link rel="prev" href="multi__main_concepts.html" title="5. Main Concepts"><link rel="next" href="multi_spring-cloud-stream-overview-binders.html" title="7. Binders"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">6. Programming Model</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi__main_concepts.html">Prev</a> </td><th width="60%" align="center">Part I. Preface</th><td width="20%" align="right"> <a accesskey="n" href="multi_spring-cloud-stream-overview-binders.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_programming_model" href="#_programming_model"></a>6. Programming Model</h2></div></div></div><p>To understand the programming model, you should be familiar with the following core concepts:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="strong"><strong>Destination Binders:</strong></span> Components responsible to provide integration with the external messaging systems.</li><li class="listitem"><span class="strong"><strong>Destination Bindings:</strong></span> Bridge between the external messaging systems and application provided <span class="emphasis"><em>Producers</em></span> and <span class="emphasis"><em>Consumers</em></span> of messages (created by the Destination Binders).</li><li class="listitem"><span class="strong"><strong>Message:</strong></span> The canonical data structure used by producers and consumers to communicate with Destination Binders (and thus other applications via external messaging systems).</li></ul></div><div class="informalfigure"><div class="mediaobject" align="center"><img src="https://raw.githubusercontent.com/spring-cloud/spring-cloud-stream/master/docs/src/main/asciidoc/images/SCSt-overview.png" align="middle" alt="SCSt overview"></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_destination_binders" href="#_destination_binders"></a>6.1 Destination Binders</h2></div></div></div><p>Destination Binders are extension components of Spring Cloud Stream responsible for providing the necessary configuration and implementation to facilitate
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integration with external messaging systems.
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This integration is responsible for connectivity, delegation, and routing of messages to and from producers and consumers, data type conversion,
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invocation of the user code, and more.</p><p>Binders handle a lot of the boiler plate responsibilities that would otherwise fall on your shoulders. However, to accomplish that, the binder still needs
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@@ -250,7 +250,7 @@ If the service activator throws a <code class="literal">RequeueCurrentMessageExc
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The error handling comes in two flavors:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="strong"><strong>application:</strong></span> The error handling is done within the application (custom error handler).</li><li class="listitem"><span class="strong"><strong>system:</strong></span> The error handling is delegated to the binder (re-queue, DL, and others). Note that the techniques are dependent on binder implementation and the
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capability of the underlying messaging middleware.</li></ul></div><p>Spring Cloud Stream uses the <a class="link" href="https://github.com/spring-projects/spring-retry" target="_top">Spring Retry</a> library to facilitate successful message processing. See <a class="xref" href="multi__programming_model.html#_retry_template" title="6.4.3 Retry Template">Section 6.4.3, “Retry Template”</a> for more details.
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However, when all fails, the exceptions thrown by the message handlers are propagated back to the binder. At that point, binder invokes custom error handler or communicates
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the error back to the messaging system (re-queue, DLQ, and others).</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_application_error_handling" href="#_application_error_handling"></a>6.4.1 Application Error Handling</h3></div></div></div><p>There are two types of application-level error handling. Errors can be handled at each binding subscription or a global handler can handle all the binding subscription errors. Let’s review the details.</p><div class="figure"><a name="d0e1515" href="#d0e1515"></a><p class="title"><b>Figure 6.1. A Spring Cloud Stream Sink Application with Custom and Global Error Handlers</b></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="https://raw.githubusercontent.com/spring-cloud/spring-cloud-stream/master/docs/src/main/asciidoc/images/custom_vs_global_error_channels.png" align="middle" alt="custom vs global error channels"></div></div></div><br class="figure-break"><p>For each input binding, Spring Cloud Stream creates a dedicated error channel with the following semantics <code class="literal"><destinationName>.errors</code>.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The <code class="literal"><destinationName></code> consists of the name of the binding (such as <code class="literal">input</code>) and the name of the group (such as <code class="literal">myGroup</code>).</p></td></tr></table></div><p>Consider the following:</p><pre class="programlisting">spring.cloud.stream.bindings.input.group=myGroup</pre><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@StreamListener(Sink.INPUT)</span></em> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// destination name 'input.myGroup'</span>
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the error back to the messaging system (re-queue, DLQ, and others).</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="_application_error_handling" href="#_application_error_handling"></a>6.4.1 Application Error Handling</h3></div></div></div><p>There are two types of application-level error handling. Errors can be handled at each binding subscription or a global handler can handle all the binding subscription errors. Let’s review the details.</p><div class="figure"><a name="d0e1506" href="#d0e1506"></a><p class="title"><b>Figure 6.1. A Spring Cloud Stream Sink Application with Custom and Global Error Handlers</b></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="https://raw.githubusercontent.com/spring-cloud/spring-cloud-stream/master/docs/src/main/asciidoc/images/custom_vs_global_error_channels.png" align="middle" alt="custom vs global error channels"></div></div></div><br class="figure-break"><p>For each input binding, Spring Cloud Stream creates a dedicated error channel with the following semantics <code class="literal"><destinationName>.errors</code>.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The <code class="literal"><destinationName></code> consists of the name of the binding (such as <code class="literal">input</code>) and the name of the group (such as <code class="literal">myGroup</code>).</p></td></tr></table></div><p>Consider the following:</p><pre class="programlisting">spring.cloud.stream.bindings.input.group=myGroup</pre><pre class="programlisting"><em><span class="hl-annotation" style="color: gray">@StreamListener(Sink.INPUT)</span></em> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-comment">// destination name 'input.myGroup'</span>
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">public</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">void</span> handle(Person value) {
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<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">throw</span> <span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">new</span> RuntimeException(<span xmlns:d="http://docbook.org/ns/docbook" class="hl-string">"BOOM!"</span>);
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}
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@@ -392,4 +392,4 @@ The <code class="literal">Publisher</code> in the following example still uses R
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e -> e.poller(p -> p.fixedDelay(<span class="hl-number">1</span>)))
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.toReactivePublisher();
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}
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}</pre></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__main_concepts.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="multi__reference_guide.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="multi_spring-cloud-stream-overview-binders.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">5. Main Concepts </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-stream.html">Home</a></td><td width="40%" align="right" valign="top"> 7. Binders</td></tr></table></div></body></html>
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}</pre></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi__main_concepts.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="multi__preface.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="multi_spring-cloud-stream-overview-binders.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">5. Main Concepts </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-stream.html">Home</a></td><td width="40%" align="right" valign="top"> 7. Binders</td></tr></table></div></body></html>
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