# Cache

## Cache Component

Available as of Apache 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.

## URI format

    cache://cacheName[?options]

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

## Options

The available options are:

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. The policy options include: `MemoryStoreEvictionPolicy.LFU`—Least frequently used. `MemoryStoreEvictionPolicy.LRU`—Least recently used. `MemoryStoreEvictionPolicy.FIFO`—First in first out, ordered 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` | Apache Camel 2.3: If you want to use a custom factory which instantiates and creates the EHCache `net.sf.ehcache.CacheManager`.

## Message Headers

Header | Description
--- | ---
`CACHE_OPERATION` | The operation to be performed on the cache. The valid options are: `ADD` `UPDATE` `DELETE` `DELETEALL`
`CACHE_KEY` | The cache key used to store the message in the cache. The cache key is optional, if the `CACHE_OPERATION` is `DELETEALL`.

## 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 `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.

## 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

## 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("CACHE_OPERATION", constant("ADD"))
         .setHeader("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("CACHE_OPERATION", constant("UPDATE"))
         .setHeader("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("CACHE_OPERATION", constant("DELETE"))
         .setHeader("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("CACHE_OPERATION", constant("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("CACHE_OPERATION");
               String key = (String) exchange.getIn().getHeader("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("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");
       }
    };

## 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.