Cache Component

Available as of Camel 2.1

The cache component enables you to perform caching operations using EHCache as the Cache Implementation. The cache itself is created on demand or if a cache of that name already exists then it is simply utilized with its original settings.

This component supports producer and event based consumer endpoints.

The Cache consumer is an event based consumer and can be used to listen and respond to specific cache activities. If you need to perform selections from a pre-existing cache, use the processors defined for the cache component.

Maven users will need to add the following dependency to their pom.xml for this component:

URI format

You can append query options to the URI in the following format, ?option=value&option=#beanRef&...

Options

Name

Default Value

Description

maxElementsInMemory

1000

The number of elements that may be stored in the defined cache

memoryStoreEvictionPolicy

MemoryStoreEvictionPolicy.LFU

The number of elements that may be stored in the defined cache. Options include

  • MemoryStoreEvictionPolicy.LFU - Least frequently used
  • MemoryStoreEvictionPolicy.LRU - Least recently used
  • MemoryStoreEvictionPolicy.FIFO - first in first out, the oldest element by creation time

overflowToDisk

true

Specifies whether cache may overflow to disk

eternal

false

Sets whether elements are eternal. If eternal, timeouts are ignored and the
element never expires.

timeToLiveSeconds

300

The maximum time between creation time and when an element expires.
Is used only if the element is not eternal

timeToIdleSeconds

300

The maximum amount of time between accesses before an element expires

diskPersistent

false

Whether the disk store persists between restarts of the Virtual Machine.

diskExpiryThreadIntervalSeconds

120

The number of seconds between runs of the disk expiry thread.

cacheManagerFactory

null

Camel 2.8: If you want to use a custom factory which instantiates and creates the EHCache net.sf.ehcache.CacheManager.

Type: abstract org.apache.camel.component.cache.CacheManagerFactory

eventListenerRegistry

null

Camel 2.8: Sets a list of EHCache net.sf.ehcache.event.CacheEventListener for all new caches- no need to define it per cache in EHCache xml config anymore.

Type: org.apache.camel.component.cache.CacheEventListenerRegistry

cacheLoaderRegistry

null

Camel 2.8: Sets a list of org.apache.camel.component.cache.CacheLoaderWrapper that extends EHCache net.sf.ehcache.loader.CacheLoader for all new caches- no need to define it per cache in EHCache xml config anymore.

Type: org.apache.camel.component.cache.CacheLoaderRegistry

key

null

Camel 2.10: To configure using a cache key by default. If a key is provided in the message header, then the key from the header takes precedence.

operation

null

Camel 2.10: To configure using an cache operation by default. If an operation in the message header, then the operation from the header takes precedence.

Cache Component options

Name

Default Value

Description

configuration

 

To use a custom org.apache.camel.component.cache.CacheConfiguration configuration.

cacheManagerFactory

 

To use a custom org.apache.camel.component.cache.CacheManagerFactory.

configurationFile

 

Camel 2.13/2.12.3: To configure the location of the ehcache.xml file to use, such as classpath:com/foo/mycache.xml to load from classpath. If no configuration is given, then the default settings from EHCache is used.

Sending/Receiving Messages to/from the cache

Message Headers up to Camel 2.7

Header

Description

CACHE_OPERATION

The operation to be performed on the cache. Valid options are

  • GET
  • CHECK
  • ADD
  • UPDATE
  • DELETE
  • DELETEALL
    GET and CHECK requires Camel 2.3 onwards.

CACHE_KEY

The cache key used to store the Message in the cache. The cache key is optional if the CACHE_OPERATION is DELETEALL

Message Headers Camel 2.8+

Header changes in Camel 2.8

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The header names and supported values have changed to be prefixed with 'CamelCache' and use mixed case. This makes them easier to identify and keep separate from other headers. The CacheConstants variable names remain unchanged, just their values have been changed. Also, these headers are now removed from the exchange after the cache operation is performed.

Header

Description

CamelCacheOperation

The operation to be performed on the cache. The valid options are

  • CamelCacheGet
  • CamelCacheCheck
  • CamelCacheAdd
  • CamelCacheUpdate
  • CamelCacheDelete
  • CamelCacheDeleteAll

CamelCacheKey

The cache key used to store the Message in the cache. The cache key is optional if the CamelCacheOperation is CamelCacheDeleteAll

The CamelCacheAdd and CamelCacheUpdate operations support additional headers:

Header

Type

Description

CamelCacheTimeToLive

Integer

Camel 2.11: Time to live in seconds.

CamelCacheTimeToIdle

Integer

Camel 2.11: Time to idle in seconds.

CamelCacheEternal

Boolean

Camel 2.11: Whether the content is eternal.

Cache Producer

Sending data to the cache involves the ability to direct payloads in exchanges to be stored in a pre-existing or created-on-demand cache. The mechanics of doing this involve

  • setting the Message Exchange Headers shown above.
  • ensuring that the Message Exchange Body contains the message directed to the cache

Cache Consumer

Receiving data from the cache involves the ability of the CacheConsumer to listen on a pre-existing or created-on-demand Cache using an event Listener and receive automatic notifications when any cache activity take place (i.e CamelCacheGet/CamelCacheUpdate/CamelCacheDelete/CamelCacheDeleteAll). Upon such an activity taking place

  • an exchange containing Message Exchange Headers and a Message Exchange Body containing the just added/updated payload is placed and sent.
  • in case of a CamelCacheDeleteAll operation, the Message Exchange Header CamelCacheKey and the Message Exchange Body are not populated.

Cache Processors

There are a set of nice processors with the ability to perform cache lookups and selectively replace payload content at the

  • body
  • token
  • xpath level

Cache Usage Samples

Example 1: Configuring the cache

Example 2: Adding keys to the cache

Example 2: Updating existing keys in a cache

Example 3: Deleting existing keys in a cache

Example 4: Deleting all existing keys in a cache

Example 5: Notifying any changes registering in a Cache to Processors and other Producers

Example 6: Using Processors to selectively replace payload with cache values

Example 7: Getting an entry from the Cache

Example 8: Checking for an entry in the Cache

Note: The CHECK command tests existence of an entry in the cache but doesn't place a message in the body.

Management of EHCache

EHCache has its own statistics and management from JMX.

Here's a snippet on how to expose them via JMX in a Spring application context:

Of course you can do the same thing in straight Java:

You can get cache hits, misses, in-memory hits, disk hits, size stats this way. You can also change CacheConfiguration parameters on the fly.

Cache replication Camel 2.8+

The Camel Cache component is able to distribute a cache across server nodes using several different replication mechanisms including: RMI, JGroups, JMS and Cache Server.

There are two different ways to make it work:

1. You can configure ehcache.xml manually

OR

2. You can configure these three options:

  • cacheManagerFactory
  • eventListenerRegistry
  • cacheLoaderRegistry

Configuring Camel Cache replication using the first option is a bit of hard work as you have to configure all caches separately. So in a situation when the all names of caches are not known, using ehcache.xml is not a good idea.

The second option is much better when you want to use many different caches as you do not need to define options per cache. This is because replication options are set per CacheManager and per CacheEndpoint. Also it is the only way when cache names are not know at the development phase.

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It might be useful to read the EHCache manual to get a better understanding of the Camel Cache replication mechanism.

Example: JMS cache replication

JMS replication is the most powerful and secured replication method. Used together with Camel Cache replication makes it also rather simple.
An example is available on a separate page.

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