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, used the processors defined for the cache component.

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

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-cache</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI format

cache://cacheName[?options]

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

Options

Name Default Value Description
maxElementsInMemory 1000 The numer 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 is never expired.
timeToLiveSeconds 300 The maximum time between creation time and when an element expires.
Is only used if the element is not eternal
timeToIdleSeconds 300 The maximum amount of time between accesses before an element expires
diskPersistent true Whether the disk store persists between restarts of the Virtual Machine.
The default value is false.
diskExpiryThreadIntervalSeconds 120 The number of seconds between runs of the disk expiry thread. The default value
is 120 seconds
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

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. The valid options are
  • GET
  • CHECK
  • ADD
  • UPDATE
  • DELETE
  • DELETEALL
    The 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
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 being 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

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

from("cache://MyApplicationCache" +
          "?maxElementsInMemory=1000" +
          "&memoryStoreEvictionPolicy=" +
              "MemoryStoreEvictionPolicy.LFU" +
          "&overflowToDisk=true" +
          "&eternal=true" +
          "&timeToLiveSeconds=300" +
          "&timeToIdleSeconds=true" +
          "&diskPersistent=true" +
          "&diskExpiryThreadIntervalSeconds=300")

Example 2: Adding keys to the cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD))
     .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};

Example 2: Updating existing keys in a cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_UPDATE))
     .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};

Example 3: Deleting existing keys in a cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_DELETE))
     .setHeader(CacheConstants.CACHE_KEY", constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};

Example 4: Deleting all existing keys in a cache

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_DELETEALL))
     .to("cache://TestCache1");
    }
};

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

RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("cache://TestCache1")
     .process(new Processor() {
        public void process(Exchange exchange)
               throws Exception {
           String operation = (String) exchange.getIn().getHeader(CacheConstants.CACHE_OPERATION);
           String key = (String) exchange.getIn().getHeader(CacheConstants.CACHE_KEY);
           Object body = exchange.getIn().getBody();
           // Do something
        }
     })
   }
};

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

RouteBuilder builder = new RouteBuilder() {
   public void configure() {
     //Message Body Replacer
     from("cache://TestCache1")
     .filter(header(CacheConstants.CACHE_KEY).isEqualTo("greeting"))
     .process(new CacheBasedMessageBodyReplacer("cache://TestCache1","farewell"))
     .to("direct:next");

    //Message Token replacer
    from("cache://TestCache1")
    .filter(header(CacheConstants.CACHE_KEY).isEqualTo("quote"))
    .process(new CacheBasedTokenReplacer("cache://TestCache1","novel","#novel#"))
    .process(new CacheBasedTokenReplacer("cache://TestCache1","author","#author#"))
    .process(new CacheBasedTokenReplacer("cache://TestCache1","number","#number#"))
    .to("direct:next");

    //Message XPath replacer
    from("cache://TestCache1").
    .filter(header(CacheConstants.CACHE_KEY).isEqualTo("XML_FRAGMENT"))
    .process(new CacheBasedXPathReplacer("cache://TestCache1","book1","/books/book1"))
    .process (new CacheBasedXPathReplacer("cache://TestCache1","book2","/books/book2"))
    .to("direct:next");
   }
};

Example 7: Getting an entry from the Cache

from("direct:start")
    // Prepare headers
    .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_GET))
    .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson")).
    .to("cache://TestCache1").
    // Check if entry was not found
    .choice().when(header(CacheConstants.CACHE_ELEMENT_WAS_FOUND).isNull()).
        // If not found, get the payload and put it to cache
        .to("cxf:bean:someHeavyweightOperation").
        .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD))
        .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
        .to("cache://TestCache1")
    .end()
    .to("direct:nextPhase");

Example 8: Checking for an entry in the Cache

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

from("direct:start")
    // Prepare headers
    .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_CHECK))
    .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson")).
    .to("cache://TestCache1").
    // Check if entry was not found
    .choice().when(header(CacheConstants.CACHE_ELEMENT_WAS_FOUND).isNull()).
        // If not found, get the payload and put it to cache
        .to("cxf:bean:someHeavyweightOperation").
        .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD))
        .setHeader(CacheConstants.CACHE_KEY, constant("Ralph_Waldo_Emerson"))
        .to("cache://TestCache1")
    .end();

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:

<bean id="ehCacheManagementService" class="net.sf.ehcache.management.ManagementService" init-method="init" lazy-init="false">
  <constructor-arg>
    <bean class="net.sf.ehcache.CacheManager" factory-method="getInstance"/>
  </constructor-arg>
  <constructor-arg>
    <bean class="org.springframework.jmx.support.JmxUtils" factory-method="locateMBeanServer"/>
  </constructor-arg>
  <constructor-arg value="true"/>
  <constructor-arg value="true"/>
  <constructor-arg value="true"/>
  <constructor-arg value="true"/>
</bean>

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

ManagementService.registerMBeans(CacheManager.getInstance(), mbeanServer, true, true, true, true);

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+

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

There are two different ways To make it work:

1. you need to configure ehcache.xml manually

OR

2. you have to take care about these three options:

  • cacheManagerFactory
  • eventListenerRegistry
  • cacheLoaderRegistry

Configuring Camel Cache replication using 1st option- the ehcache.xml file is a bit hard work as you have to configure all caches separately. So in a situation when the all names of caches are not know, 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.

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

Example: JMS cache replication

JMS replication is the most powerful and secured way. Used altogether with Camel Cache replication options is also the most easy way.
This example is available on separated page.

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