Apache Camel: Cache

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.

URI format

cache://cacheName[?options]

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

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

Sending/Receiving Messages to/from the cache

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

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("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");
   }
};