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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.

The Cache 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 given 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.

c> There are 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

This component supports producer and event based consumer endpoints.

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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]

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

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Sending/Receiving Messages to/from the cache

Sending data to the cache involves setting the Message Exchange Headers given in the section below.

Message Headers

Cache Producer

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In the following example, we fetch the rows from the customer table.

First we register our datasource in the Camel registry as testdb:

Wiki Markup
{snippet:id=register|lang=java|url=camel/trunk/components/camel-jdbc/src/test/java/org/apache/camel/component/jdbc/JdbcRouteTest.java}

Then we configure a route that routes to the JDBC component, so the SQL will be executed. Note how we refer to the testdb datasource that was bound in the previous step:

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{snippet:id=route|lang=java|url=camel/trunk/components/camel-jdbc/src/test/java/org/apache/camel/component/jdbc/JdbcRouteTest.java}

Or you can create a DataSource in Spring like this:

Wiki Markup
{snippet:id=example|lang=java|url=camel/trunk/components/camel-jdbc/src/test/resources/org/apache/camel/component/jdbc/camelContext.xml}

We create an endpoint, add the SQL query to the body of the IN message, and then send the exchange. The result of the query is returned in the OUT body:

Wiki Markup
{snippet:id=invoke|lang=java|url=camel/trunk/components/camel-jdbc/src/test/java/org/apache/camel/component/jdbc/JdbcRouteTest.java}

Sample - Polling the database every minute

If we want to poll a database using the JDBC component, we need to combine it with a polling scheduler such as the Timer or Quartz etc. In the following example, we retrieve data from the database every 60 seconds:

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from("timer://foo?period=60000").setBody(constant("select * from customer")).to("jdbc:testdb").to("activemq:queue:customers");

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

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
        } 
     })
   } 
};

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