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Stream caching

While stream types (like StreamSource, InputStream and Reader) are commonly used in messaging for performance reasons, they also have an important drawback: they can only be read once. In order to be able to work with message content multiple times, the stream needs to be cached.

Streams are caching in memory. In Camel 2.0, large stream messages (over 64 Kb) will be cached in a temporary file instead – Camel itself will handle deleting the temporary file once the cached stream is no longer necessary.

In Camel 2.0 stream cache is default disabled out of the box.
In Camel 1.x stream cache is default enabled out of the box.

StreamCache Affects your payload object

The StreamCache will affect your payload object as it will replace the Stream payload with a org.apache.camel.StreamCache object.
This StreamCache is capable of being re-readable and thus possible to better be routed within Camel using redelivery or Content Based Router or the likes.

However to not change the payload under the covers without the end user really knowing we changed the default in Camel 2.0 to disabled. So in Camel 2.0 you have to explicit enable it if you want to use it.

Enabling stream caching

In Apache Camel, you can explicitly enable stream caching for a single route with the streamCaching DSL method:

from("jbi:service:http://foo.bar.org/MyService")
    .streamCaching()
    .to("jbi:service:http://foo.bar.org/MyOtherService");

In Spring XML you enable it by setting the streamCaching="true" attribute on the route tag.

<route streamCaching="true">
   <from uri="jbi:service:http://foo.bar.org/MyService"/>
   <to uri="jbi:service:http://foo.bar.org/MyOtherService"/>
</route>

Scopes

StreamCache supports the global and per route scope. So by setting the streamCache attribute on camelContext you can enable/disable it globally.

<camelContext streamCache="true">
   ...
</camelContext>

The route scope is configured by the {{streamCache}} attribute on the {{<route>}} tag such as:
{code:xml}
<route streamCaching="true">
   <from uri="jbi:service:http://foo.bar.org/MyService"/>
   <to uri="jbi:service:http://foo.bar.org/MyOtherService"/>
</route>

You can mix and match for instance you can enable it globally and disable it on a particular route such as:

<camelContext streamCache="true">
  <route>
    <from uri="jbi:service:http://foo.bar.org/MyService"/>
    <to uri="jbi:service:http://foo.bar.org/MyOtherService"/>
  </route>
  
  <route streamCache="false">
    <from uri="jms:queue:foo"/>
    <to uri="jms:queue:bar"/>
  </route>

</camelContext>

Enabling from Java DSL

In Camel 2.0 you can enable stream cache by setting the property on CamelContext, for instance in a RouteBuilder class:

  context.setStreamCache(true);

  from("jbi:service:http://foo.bar.org/MyService")
     .to("jbi:service:http://foo.bar.org/MyOtherService");

Implicitly enabled for multicast and dead letter channel (Camel 1.x)

Some EIPs require that the message content can be read multiple times. Stream caching will be automatically enabled when using these EIPs in your routes:

  • Multicast will implicitly cache streams to ensure that all the endpoints can access the message content
  • Dead Letter Channel uses stream caching to ensure that the message content can actually be read again when redelivering a message

How it works?

In order to determine if a type requires caching, we leverage the type converter feature. Any type that requires stream caching can be converted into an org.apache.camel.StreamCache instance.

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