Stream caching

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.

By default, 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 enabled out of the box.
In Camel 1.x the stream cache has to be manually enabled.

Using stream caching with Camel 1.x

Explicitly enabling stream caching (Camel 1.x)

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>

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.