Stream caching
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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 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 Camel 1.x stream cache is default enabled out of the box.

StreamCache Affects your payload object

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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.

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If using Camel 2.12 onwards then see about StreamCachingStrategy further below which is the recommended way to configure stream caching options.

Enabling stream caching

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.

Scopes

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:

Enabling from Java DSL

You can enable stream cache by setting the property on CamelContext, for instance in a RouteBuilder class:

Disable stream caching explicitly

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.

Spring DSL:

Java DSL:

Streaming cache to files

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:

Property

Default

Description

CamelCachedOutputStreamBufferSize

2kb

Camel 2.9.4, 2.10.2, 2.11.0: Size in bytes of the buffer used in the stream.

CamelCachedOutputStreamThreshold

64kb or 128kb

64kb for Camel 2.11 or older. 128kb for Camel 2.12 onwards. Size in bytes when the stream should be spooled to disk instead of keeping in memory. Use a value of 0 or negative to disable it all together so streams is always kept in memory regardless of their size.

CamelCachedOutputStreamOutputDirectory

java.io.tmpdir

Base directory where temporary files for spooled streams should be stored.

CamelCachedOutputStreamCipherTransformation

null

Camel 2.11.0: If set, the temporary files are encrypted using the specified cipher transformation (i.e., a valid stream or 8-bit cipher name such as "RC4", "AES/CTR/NoPadding". An empty name "" is treated as null).

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

Disabling spooling to disk

You can disable spooling to disk by setting a threshold of 0 or a negative value.

And in XML you do

Using StreamCachingStrategy

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 old kind of configuration using properties on the CamelContext has been marked as deprecated.

The strategy has the following options:

Option

Default

Description

spoolDirectory

${java.io.tmpdir}/camel/camel-tmp-#uuid#

Base directory where temporary files for spooled streams should be stored. This option supports naming patterns as documented below.

spoolChiper

null

If set, the temporary files are encrypted using the specified cipher transformation (i.e., a valid stream or 8-bit cipher name such as "RC4", "AES/CTR/NoPadding". An empty name "" is treated as null).

spoolThreshold

128kb

Size in bytes when the stream should be spooled to disk instead of keeping in memory. Use a value of 0 or negative to disable it all together so streams is always kept in memory regardless of their size.

spoolUsedHeapMemoryThreshold

0

A percentage (1 to 99) of current used heap memory to use as threshold for spooling streams to disk. The upper bounds is based on heap committed (guaranteed memory the JVM can claim). This can be used to spool to disk when running low on memory.

spoolUsedHeapMemoryLimit

Max

If spoolUsedHeapMemoryThreshold is in use, then whether the used heap memory upper limit is either Max or Committed.

anySpoolRules

false

Whether any or all SpoolRule}}s must return {{true to determine if the stream should be spooled or not. This can be used as applying AND/OR binary logic to all the rules. By default its AND based.

bufferSize

4096

Initial size if in-memory created stream buffers.

removeSpoolDirectoryWhenStopping

true

Whether to remove the spool directory when stopping CamelContext.

statisticsEnabled

false

Whether utilization statistics is enabled. By enabling this you can see these statics for example with JMX.

SpoolDirectory naming pattern

The following patterns is supported:

  • #uuid# = a random UUID
  • #camelId# = the CamelContext id (eg the name)
  • #name# - same as #camelId#
  • #counter# - an incrementing counter
  • #bundleId# - the OSGi bundle id (only for OSGi environments)
  • #symbolicName# - the OSGi symbolic name (only for OSGi environments)
  • #version# - the OSGi bundle version (only for OSGi environments)
  • ${env:key} - the environment variable with the key
  • ${key} - the JVM system property with the key

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

Using StreamCachingStrategy in Java

You can configure the StreamCachingStrategy in Java as shown below:

And remember to enable Stream caching on the CamelContext or on routes

Using StreamCachingStrategy in XML

And in XML you do:

You can also define a <bean> instead of using the <streamCaching> tag:

And in XML you do

Using spoolUsedHeapMemoryThreshold

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:

Using custom SpoolRule implementations

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.

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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