Developed a camel-cache component to store, perform lookups and listen for cache events on a camel route

I have recently submitted a Camel cache component which is slated for release in Apache Camel version 2.1 in Septermber, 09

http://issues.apache.org/activemq/browse/CAMEL-1868

The Camel Caching component has the following abilities

a> In Producer mode, the component provides the ability to direct payloads in exchanges to a stored in a pre-existing or created-on-demand Cache. The producer mode supports operations to ADD/UPDATE/DELETE/DELETEALL elements in a cache. (Examples goven below)

b> In Consumer mode, the component provides the ability 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 header elements describing the operation and cachekey and a body containing the just added/updated payload is placed and sent. In case of a DELETEALL operation the body of the exchanage is not populated.

The cache itself may be created on demand or if a cache of that name already exists then it is simply utilized with its original settings. The URL itself may take the following form

Configuring the cache

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

// Note that all the attributes of the above URL are 
// standard ehCache settings that may be set at 
// Cache creation.

Given below are examples of how to create/set routes:

Producer Example 1: Adding keys to the cache with a body received from direct:start

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")
   }
};

Producer Example 2: Updating existing keys in a cache with a body received from direct:start

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")
   }
};

Producer Example 3: Deleting existing keys in a cache with a body received from direct:start

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")
   }
};

Producer Example 4: Deleting all keys in a cache with a body received from direct:start

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");

     from("direct:start")
     .setHeader("CACHE_OPERATION", constant("ADD"))
     .setHeader("CACHE_KEY", constant("Ralph_Waldo_Emerson2"))
     .to("cache://TestCache1");

     from("direct:start")
     .setHeader("CACHE_OPERATION", constant("DELETEALL"))
     .to("cache://TestCache1");
    }
};

Consumer Example 1: Notifying any changes registering in a Cache to Processors and other Producers

// Note: in this example the consumer is 
//     created first and then 3 routes 
//     send different message as Cache 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
        } 
     })
   } 
};

I have added a set of nice processors to the camel-cache component to provide the ability to perform cache lookups and selectively replace payload content at the
- body
- token
- xpath level

The mechanics of doing this are as follows

Producer Example 3: Deleting existing keys in a cache with a body received from direct:start

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");

    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");
   }
};