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Chapter 12. Cache

12.1. Cache Component
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Available as of Camel 2.1
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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: 
<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>
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URI format
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cache://cacheName[?options]
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You can append query options to the URI in the following format, ?option=value&option=#beanRef&...

Options
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The Cache component supports the following options:
Expand
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.

Message Headers Camel 2.8\+
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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
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 removed from the exchange after the cache operation is performed.
The CamelCacheAdd and CamelCacheUpdate operations support additional headers:
Expand
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
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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
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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
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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

Example 1: Configuring the cache
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from("cache://MyApplicationCache" +
          "?maxElementsInMemory=1000" +
          "&memoryStoreEvictionPolicy=" +
              "MemoryStoreEvictionPolicy.LFU" +
          "&overflowToDisk=true" +
          "&eternal=true" +
          "&timeToLiveSeconds=300" +
          "&timeToIdleSeconds=true" +
          "&diskPersistent=true" +
          "&diskExpiryThreadIntervalSeconds=300")
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Example 2: Adding keys to the cache
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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")
   }
};
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Example 2: Updating existing keys in a cache
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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")
   }
};
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Example 3: Deleting existing keys in a cache
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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")
   }
};
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Example 4: Deleting all existing keys in a cache
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RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_DELETEALL))
     .to("cache://TestCache1");
    }
};
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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
        }
     })
   }
};
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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");
   }
};
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Example 7: Getting an entry from the Cache
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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");
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Example 8: Checking for an entry in the Cache
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Note: The CHECK command tests existence of an entry in the cache but doesn't place a message in 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();
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Management of EHCache
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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>
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Of course you can do the same thing in straight Java: 
ManagementService.registerMBeans(CacheManager.getInstance(), mbeanServer, true, true, true, true);
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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\+
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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.
Note
It might be useful to read the EHCache manual to get a better understanding of the Camel Cache replication mechanism.

Example: JMS cache replication
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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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