SpringCloud/spring-cloud-function
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
2019-09-10 08:55:25 +00:00
parent bb1e15e749
commit 1fb056edec
1 changed files with 55 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

66
reference/html/spring-cloud-function.html
View File

@@ -494,33 +494,77 @@ This feature is very useful in certain FAAS environments where maintaining confi
for several functions could be cumbersome or exposing more then one function is not possible.</p>
</div>
<div class="paragraph">
<p>You enable this feature via <code>spring.cloud.function.routing.enabled</code> property setting it
to <code>true</code> (default is <code>false</code>).
This enables <code>RoutingFunction</code> under the name <code>router</code> which is loaded in FunctionCatalog.</p>
<p>The <code>RoutingFunction</code> is registered in <em>FunctionCatalog</em> under the name <code>functionRouter</code>. For simplicity
and consistency you can also refer to <code>RoutingFunction.FUNCTION_NAME</code> constant.</p>
</div>
<div class="paragraph">
<p>This function has the following signature:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">public class RoutingFunction implements Function&lt;Publisher&lt;Message&lt;?&gt;&gt;, Publisher&lt;?&gt;&gt;, Consumer&lt;Publisher&lt;Message&lt;?&gt;&gt;&gt; {
<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">public class RoutingFunction implements Function&lt;Object, Object&gt; {
. . .
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>This allows the above function to act as both <code>Function</code> and <code>Consumer</code>.
As you can see it takes <code>Message&lt;?&gt;</code> as an input argument. This allows you to communicate
the name of the actual function you want to invoke by providing <code>function.name</code> Message header.</p>
<p>The routing instructions could be communicated in several ways;</p>
</div>
<div class="paragraph">
<p>In specific execution environments/models the adapters are responsible to translate and communicate <code>function.name</code>
via Message header. For example, when using <em>spring-cloud-function-web</em> you can provide <code>function.name</code> as an HTTP
<p><strong>Message Headers</strong></p>
</div>
<div class="paragraph">
<p>If the input argument is of type <code>Message&lt;?&gt;</code>, you can communicate routing instruction by setting one of
<code>spring.cloud.function.definition</code> or <code>spring.cloud.function.routing-expression</code> Message headers.
For more static cases you can use <code>spring.cloud.function.definition</code> header which allows you to provide
the name of a single function (e.g., <code>&#8230;&#8203;definition=foo</code>) or a composition instruction (e.g., <code>&#8230;&#8203;definition=foo|bar|baz</code>).
For more dynamic cases you can use <code>spring.cloud.function.routing-expression</code> header which allows
you to use Spring Expression Language (SpEL) and provide SpEL expression that should resolve
into definition of a function (as described above).</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
SpEL evaluation context&#8217;s root object is the
actual input argument, so in he case of <code>Message&lt;?&gt;</code> you can construct expression that has access
to both <code>payload</code> and <code>headers</code> (e.g., <code>spring.cloud.function.routing-expression=headers.function_name</code>).
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>In specific execution environments/models the adapters are responsible to translate and communicate
<code>spring.cloud.function.definition</code> and/or <code>spring.cloud.function.routing-expression</code> via Message header.
For example, when using <em>spring-cloud-function-web</em> you can provide <code>spring.cloud.function.definition</code> as an HTTP
header and the framework will propagate it as well as other HTTP headers as Message headers.</p>
</div>
<div class="paragraph">
<p>Using Message also allows us to benefit from `MessageConverter`s to convert incoming request to the actual input type
of the target function</p>
<p><strong>Application Properties</strong></p>
</div>
<div class="paragraph">
<p>Routing instruction can also be communicated via <code>spring.cloud.function.definition</code>
or <code>spring.cloud.function.routing-expression</code> as application properties. The rules described in the
previous section apply here as well. The only difference is you provide these instructions as
application properties (e.g., <code>--spring.cloud.function.definition=foo</code>).</p>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">
<i class="fa icon-important" title="Important"></i>
</td>
<td class="content">
When dealing with reactive inputs (e.g., Publisher), routing instructions must only be provided via Function properties. This is
due to the nature of the reactive functions which are invoked only once to pass a Publisher and the rest
is handled by the reactor, hence we can not access and/or rely on the routing instructions communicated via individual
values (e.g., Message).
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">