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h2. 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:
{code:xml}
<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>
{code}

h3. URI format

{code}
cache://cacheName[?options]
{code}

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

h3. Options
{div:class=confluenceTableSmall}
|| 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 2.3:* If you want to use a custom factory which instantiates and creates the EHCache {{net.sf.ehcache.CacheManager}}. |
{div}

h3. Sending/Receiving Messages to/from the cache

h4. Message Headers
{div:class=confluenceTableSmall}
|| 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 |
{div}


h4. 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

h4. 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 ADD/UPDATE/DELETE/DELETEALL). 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 DELETEALL operation, the Message Exchange Header CACHE_KEY and the Message Exchange Body are not populated.

h4. 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

h3. Cache Usage Samples

h4. Example 1: Configuring the cache
{code}
from("cache://MyApplicationCache" +
          "?maxElementsInMemory=1000" + 
          "&memoryStoreEvictionPolicy=" +
              "MemoryStoreEvictionPolicy.LFU" +
          "&overflowToDisk=true" +
          "&eternal=true" +
          "&timeToLiveSeconds=300" + 
          "&timeToIdleSeconds=true" +
          "&diskPersistent=true" +
          "&diskExpiryThreadIntervalSeconds=300")
{code}

h4. Example 2: Adding keys to the cache 
{code}
RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader("CACHE_OPERATION", constant("ADD"))
     .setHeader("CACHE_KEY", constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};
{code}

h4. Example 2: Updating existing keys in a cache 
{code}
RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader("CACHE_OPERATION", constant("UPDATE"))
     .setHeader("CACHE_KEY", constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};
{code}

h4. Example 3: Deleting existing keys in a cache 
{code}
RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader("CACHE_OPERATION", constant("DELETE"))
     .setHeader("CACHE_KEY", constant("Ralph_Waldo_Emerson"))
     .to("cache://TestCache1")
   }
};
{code}

h4. Example 4: Deleting all existing keys in a cache 
{code}
RouteBuilder builder = new RouteBuilder() {
    public void configure() {
     from("direct:start")
     .setHeader("CACHE_OPERATION", constant("DELETEALL"))
     .to("cache://TestCache1");
    }
};
{code}

h4. Example 5: Notifying any changes registering in a Cache to Processors and other Producers
{code}
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("CACHE_OPERATION");
           String key = (String) exchange.getIn().getHeader("CACHE_KEY");
           Object body = exchange.getIn().getBody();
           // Do something
        } 
     })
   } 
};
{code}

h4. Example 6: Using Processors to selectively replace payload with cache values
{code}
RouteBuilder builder = new RouteBuilder() {
   public void configure() {
     //Message Body Replacer
     from("cache://TestCache1")
     .filter(header("CACHE_KEY").isEqualTo("greeting"))
     .process(new CacheBasedMessageBodyReplacer("cache://TestCache1","farewell"))
     .to("direct:next");  

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

h4. Example 7: Getting an entry from the Cache
{code}
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");
{code}

h4. 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.
{code}
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();
{code}


h3. Management of EHCache

EHCache has its own statistics and management from [JMX|Camel JMX].

Here's a snippet on how to expose them via JMX in a Spring application context:
{code:xml}
<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>
{code}

Of course you can do the same thing in straight Java:
{code:java}
ManagementService.registerMBeans(CacheManager.getInstance(), mbeanServer, true, true, true, true);
{code}

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