SpringCloud/spring-cloud-stream
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Sync docs from master to gh-pages

Browse Source
This commit is contained in:
buildmaster
2018-12-12 19:08:39 +00:00
parent 8d032cc516
commit e6f32a61ed
9 changed files with 43 additions and 38 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
multi/multi_schema-evolution.html
View File

@@ -79,10 +79,10 @@ If you want to use the Confluent schema registry, you need to create a bean of t
<span xmlns:d="http://docbook.org/ns/docbook" class="hl-keyword">return</span> client;
}</pre><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 ConfluentSchemaRegistryClient is tested against Confluent platform version 4.0.0.</p></td></tr></table></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="_schema_registration_and_resolution" href="#_schema_registration_and_resolution"></a>10.6&nbsp;Schema Registration and Resolution</h2></div></div></div><p>To better understand how Spring Cloud Stream registers and resolves new schemas and its use of Avro schema comparison features, we provide two separate subsections:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="quote">&#8220;<span class="quote"><a class="xref" href="multi_schema-evolution.html#spring-cloud-stream-overview-schema-registration-process" title="10.6.1&nbsp;Schema Registration Process (Serialization)">Section&nbsp;10.6.1, &#8220;Schema Registration Process (Serialization)&#8221;</a></span>&#8221;</span></li><li class="listitem"><span class="quote">&#8220;<span class="quote"><a class="xref" href="multi_schema-evolution.html#spring-cloud-stream-overview-schema-resolution-process" title="10.6.2&nbsp;Schema Resolution Process (Deserialization)">Section&nbsp;10.6.2, &#8220;Schema Resolution Process (Deserialization)&#8221;</a></span>&#8221;</span></li></ul></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="spring-cloud-stream-overview-schema-registration-process" href="#spring-cloud-stream-overview-schema-registration-process"></a>10.6.1&nbsp;Schema Registration Process (Serialization)</h3></div></div></div><p>The first part of the registration process is extracting a schema from the payload that is being sent over a channel.
Avro types such as <code class="literal">SpecificRecord</code> or <code class="literal">GenericRecord</code> already contain a schema, which can be retrieved immediately from the instance.
In the case of POJOs, a schema is inferred if the <code class="literal">spring.cloud.stream.schema.avro.dynamicSchemaGenerationEnabled</code> property is set to <code class="literal">true</code> (the default).</p><div class="figure"><a name="d0e4089" href="#d0e4089"></a><p class="title"><b>Figure&nbsp;10.1.&nbsp;Schema Writer Resolution Process</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/schema_resolution.png" align="middle" alt="schema resolution"></div></div></div><br class="figure-break"><p>Ones a schema is obtained, the converter loads its metadata (version) from the remote server.
In the case of POJOs, a schema is inferred if the <code class="literal">spring.cloud.stream.schema.avro.dynamicSchemaGenerationEnabled</code> property is set to <code class="literal">true</code> (the default).</p><div class="figure"><a name="d0e4090" href="#d0e4090"></a><p class="title"><b>Figure&nbsp;10.1.&nbsp;Schema Writer Resolution Process</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/schema_resolution.png" align="middle" alt="schema resolution"></div></div></div><br class="figure-break"><p>Ones a schema is obtained, the converter loads its metadata (version) from the remote server.
First, it queries a local cache. If no result is found, it submits the data to the server, which replies with versioning information.
The converter always caches the results to avoid the overhead of querying the Schema Server for every new message that needs to be serialized.</p><div class="figure"><a name="d0e4100" href="#d0e4100"></a><p class="title"><b>Figure&nbsp;10.2.&nbsp;Schema Registration Process</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/registration.png" align="middle" alt="registration"></div></div></div><br class="figure-break"><p>With the schema version information, the converter sets the <code class="literal">contentType</code> header of the message to carry the version information&#8201;&#8212;&#8201;for example: <code class="literal">application/vnd.user.v1+avro</code>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="spring-cloud-stream-overview-schema-resolution-process" href="#spring-cloud-stream-overview-schema-resolution-process"></a>10.6.2&nbsp;Schema Resolution Process (Deserialization)</h3></div></div></div><p>When reading messages that contain version information (that is, a <code class="literal">contentType</code> header with a scheme like the one described under <span class="quote">&#8220;<span class="quote"><a class="xref" href="multi_schema-evolution.html#spring-cloud-stream-overview-schema-registration-process" title="10.6.1&nbsp;Schema Registration Process (Serialization)">Section&nbsp;10.6.1, &#8220;Schema Registration Process (Serialization)&#8221;</a></span>&#8221;</span>), the converter queries the Schema server to fetch the writer schema of the message.
Once it has found the correct schema of the incoming message, it retrieves the reader schema and, by using Avro&#8217;s schema resolution support, reads it into the reader definition (setting defaults and any missing properties).</p><div class="figure"><a name="d0e4128" href="#d0e4128"></a><p class="title"><b>Figure&nbsp;10.3.&nbsp;Schema Reading Resolution Process</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/schema_reading.png" align="middle" alt="schema reading"></div></div></div><br class="figure-break"><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>You should understand the difference between a writer schema (the application that wrote the message) and a reader schema (the receiving application).
The converter always caches the results to avoid the overhead of querying the Schema Server for every new message that needs to be serialized.</p><div class="figure"><a name="d0e4101" href="#d0e4101"></a><p class="title"><b>Figure&nbsp;10.2.&nbsp;Schema Registration Process</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/registration.png" align="middle" alt="registration"></div></div></div><br class="figure-break"><p>With the schema version information, the converter sets the <code class="literal">contentType</code> header of the message to carry the version information&#8201;&#8212;&#8201;for example: <code class="literal">application/vnd.user.v1+avro</code>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="spring-cloud-stream-overview-schema-resolution-process" href="#spring-cloud-stream-overview-schema-resolution-process"></a>10.6.2&nbsp;Schema Resolution Process (Deserialization)</h3></div></div></div><p>When reading messages that contain version information (that is, a <code class="literal">contentType</code> header with a scheme like the one described under <span class="quote">&#8220;<span class="quote"><a class="xref" href="multi_schema-evolution.html#spring-cloud-stream-overview-schema-registration-process" title="10.6.1&nbsp;Schema Registration Process (Serialization)">Section&nbsp;10.6.1, &#8220;Schema Registration Process (Serialization)&#8221;</a></span>&#8221;</span>), the converter queries the Schema server to fetch the writer schema of the message.
Once it has found the correct schema of the incoming message, it retrieves the reader schema and, by using Avro&#8217;s schema resolution support, reads it into the reader definition (setting defaults and any missing properties).</p><div class="figure"><a name="d0e4129" href="#d0e4129"></a><p class="title"><b>Figure&nbsp;10.3.&nbsp;Schema Reading Resolution Process</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/schema_reading.png" align="middle" alt="schema reading"></div></div></div><br class="figure-break"><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>You should understand the difference between a writer schema (the application that wrote the message) and a reader schema (the receiving application).
We suggest taking a moment to read <a class="link" href="https://avro.apache.org/docs/1.7.6/spec.html" target="_top">the Avro terminology</a> and understand the process.
Spring Cloud Stream always fetches the writer schema to determine how to read a message.
If you want to get Avro&#8217;s schema evolution support working, you need to make sure that a <code class="literal">readerSchema</code> was properly set for your application.</p></td></tr></table></div></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi_content-type-management.html">Prev</a>&nbsp;</td><td width="20%" align="center"><a accesskey="u" href="multi__preface.html">Up</a></td><td width="40%" align="right">&nbsp;<a accesskey="n" href="multi__inter_application_communication.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">9.&nbsp;Content Type Negotiation&nbsp;</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">&nbsp;11.&nbsp;Inter-Application Communication</td></tr></table></div></body></html>