Camel allows you to proxy a producer sending to an Endpoint by a regular interface. Then when clients using this interface can work with it as if its regular java code but in reality its proxied and does a Request Reply to a given endpoint.
You can define a proxy in the spring XML file as shown below
Now the client can grab this bean using regular spring bean coding and invoke it as if its just another bean.
You can also create a proxy from regular Java using a org.apache.camel.component.bean.ProxyHelper as shown below:
In Camel 2.3 you can use org.apache.camel.builder.ProxyBuilder which may be easier to use than ProxyHelper:
Another way to configure the proxy from java is by using the @Produce annotation. Also see POJO Producing.
This basically does the same as ProxyHelper.createProxy.
When using a proxy Camel will send the message payload as a org.apache.camel.component.bean.BeanInvocation object which holds the details of which method was invoked and what the argument was.
Available as of Camel 2.1
If you proxied method signature only have one parameter such as:
Then it gives another advantage in Camel as it allows Camel to regard the value passed in to this single parameter as the real payload. In other words if you pass in Camel to the hello method, then Camel can see that as a java.lang.String payload with the value of Camel. This gives you a great advantage as you can use the proxy as first class services with Camel.
You can proxy Camel and let clients use the pure and clean interfaces as if Camel newer existed. Then Camel can proxy the invocation and receive the input passed into the single method parameter and regard that as if it was just the message payload.
Okay lets try that with an example
At first we have the interface we wish to proxy
Notice that all methods have single parameters. The return type is optional, as you can see one of them is void.
This allows us to easily use org.w3c.dom.Document and String types with no hazzle.
Now there is a couple of tests that shows using the Camel Proxy how we can easily invoke the proxy and do not know its actually Camel doing some routing underneath.
And this one below shows using different types that Camel adapts to.
Isn't this cool?
Available as of Camel 2.8
By default the Camel Proxy invocation is synchronous when invoked from the client. If you want this to be asynchronous you define the return type to be of java.util.concurrent.Future type. The Future is a handle to the task which the client can use to obtain the result.
For example given this client interface
The client can use this with a Camel Proxy as shown from the following snippet from an unit test:
This allows you to fully define your client API without any Camel dependency at all, and decide whether the invocation should be synchronous or asynchronous.
If the Client is asynchronous (return type is Future) then Camel will continue processing the invocation using a thread pool which is being looked up using the key CamelInvocationHandler. Its a shared thread pool for all Camel Proxy in the CamelContext. You can define a thread pool profile with the id CamelInvocationHandler to configure settings such as min/max threads etc.