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 in Camel 2.11 or older, and 128 kb from Camel 2.12 onwards) 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 Apache Camel, you can explicitly enable stream caching for a single route with the streamCaching DSL method:
In Spring XML you enable it by setting the streamCache="true" attribute on the route tag.
StreamCache supports the global and per route scope. So by setting the streamCache attribute on camelContext you can enable/disable it globally.
The route scope is configured by the streamCache attribute on the <route> tag such as:
You can mix and match for instance you can enable it globally and disable it on a particular route such as:
You can enable stream cache by setting the property on CamelContext, for instance in a RouteBuilder class:
If you have enabled stream caching globally on the CamelContext and you want to disable it for certain routes in a selective manner, you can use the following syntax.
When stream cache is enabled it will by default spool big streams to files instead of keeping them in memory. The default threshold is 64kb but you can configure it with the following properties:
You set these properties on the CamelContext as shown below, where we use a 1mb threshold to spool to disk for messages bigger than 1mb:
And in XML you do
You can disable spooling to disk by setting a threshold of 0 or a negative value.
And in XML you do
Available as of Camel 2.12
Stream caching is from Camel 2.12 onwards intended to be configured using org.apache.camel.spi.StreamCachingStrategy.
The strategy has the following options:
The following patterns is supported:
A could of examples, to store in the java temp directory with a sub directory using the CamelContext name:
To store in KARAF_HOME/tmp/bundleId directory
You can configure the StreamCachingStrategy in Java as shown below:
And in XML you do:
You can also define a <bean> instead of using the <streamCaching> tag:
And in XML you do
By default stream caching will spool only big payloads (128kb or bigger) to disk. However you can also set the spoolUsedHeapMemoryThreshold option which is a percentage of used heap memory. This can be used to also spool to disk when running low on memory.
For example with:
Then notice that as spoolThreshold is default enabled with 128kb, then we have both thresholds in use (spoolThreshold and spoolUsedHeapMemoryThreshold). And in this example then we only spool to disk if payload is > 128kb and that used heap memory is > 70%. The reason is that we have the option anySpoolRules as default false. That means both rules must be true (eg AND).
If we want to spool to disk if either of the rules (eg OR), then we can do:
If we only want to spool to disk if we run low on memory then we can set:
... then we do not use the spoolThreshold rule, and only the heap memory based is in use.
By default the upper limit of the used heap memory is based on the maximum heap size. Though you can also configure to use the committed heap size as the upper limit, this is done using the spoolUsedHeapMemoryThreshold option as shown below:
You can implement your custom rules to determine if the stream should be spooled to disk. This can be done by implementing the interface org.apache.camel.spi.StreamCachingStrategy.SpoolRule which has a single method:
The length is the length of the stream.
To use the rule then add it to the StreamCachingStrategy as shown below:
And from XML you need to define a <bean> with your custom rule
Using the spoolRules attribute on <streamCaching>. if you have more rules, then separate them by comma.
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.