Apache Camel - Components


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Camel provides several pre-built components.

In this chapter, we will discuss a few important components from the camel-core module.

Bean

The Bean component binds beans to Camel message exchanges. The URI to create an Endpoint is specified as bean:beanID, where beanID is the name of the bean as specified in the Registry.

JndiContext jndiContext = new JndiContext();
jndiContext.bind("MilkOrder", new MilkOrderProcessor());
CamelContext camelContext = new DefaultCamelContext(jndiContext);

camelContext.addRoutes(new RouteBuilder() {
   public void configure() {
      from("direct:bigBasket")
         .to("bean:MilkOrder?method=placeOrder");
   }
});

Note how the endpoint is specified using the bean: protocol. You may optionally specify the bean method that is to be invoked; in this case, the method called placeOrder will be invoked while evaluating the Endpoint expression. The MilkOrder is a JNDI name to the MilkOrderProcessor Javabean as registered in the first two lines of the code snippet. The definition of MilkOrderProcessor itself is omitted here for brevity.

Direct

You must have noticed the use of Direct in our previous examples. To send an order to an oil vendor, we used direct:oil in the Endpoint specification. The use of Direct component allows you to synchronously invoke an endpoint. The following two code snippets from our previous examples illustrate the use of Direct

.when(header("order").isEqualTo("oil"))
   .to("direct:oil")

And,

from("direct:DistributeOrderDSL")
   .process(myProcessor);

File

The File component provides access to the file system on your machine. Using this component, you will be able to save messages from other components to a local disk. In addition, it allows other Camel components to process the local files. You may use either file:directoryName[?options] or file://directoryName[?options] as a URI format while using the File component. You have earlier seen the use of this component −

from ("file:/order").to("jms:orderQueue");

Note that the File component by default takes the directory name. Therefore, the contents of the order directory will be taken as input contents. To specify a particular file in the order directory, you will use the following statement -

from ("file:/order?fileName=order.xml").to("jms:orderQueue");

Log

The Log component allows you to log messages to the underlying logging mechanism. Camel uses Simple Logging Facade for Java (SLF4J) as an abstraction to various logging frameworks. You may use java.util.logging, logback, log4j for logging. This code snippet illustrates the use of the Log component −

from("direct:DistributeOrderDSL")
   .to("bean:MilkOrder?method=placeOrder")
   .to("log:com.example.com?level=INFO&showBody=true");

SEDA

The SEDA component allows you to asynchronously call another endpoint in the same CamelContext. If you want to call across CamelContext instances, you need to use VM component. The use of SEDA is illustrated here −

from("direct:DistributeOrderDSL")
// send it to the seda queue that is async
   .to("seda:nextOrder")

In this route, we will simply route the orders to nextOrder asynchronous queue. A client who has subscribed to this queue will pick up the messages from this queue.

Timer

The Timer component is used for sending out messages at regular intervals and can thus be very useful while testing Camel applications. The code snippet here fires a test message to the console every two seconds -

from("timer://testTimer?period=2000")
   .setBody()
   .simple("This is a test message ${header.timer}")
      .to("stream:out");
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