I've been poring over the Apache Camel docs trying to get a concrete understanding of two of its most basic concepts (endpoints and routes), and although these terms are used everywhere throughout the docs, I can find no reference that actually defines what they are and what they are used for. And although their names are fairly obvious-sounding, and I think I understand what they are, I've now been assigned to a task that has landed me neck-deep in Apache Camel Land, and its absolutely vital that I understand what these mechanisms are.
My guess is that an "endpoint" is just a bean - one that can be configured in a config file like any other - that maps a name to a URI/port combo (this taken from the W3C docs). In the context of Apache Camel, my guess is that endpoints are used to connect components together, so that "routes" (connections/maps) can be formed between them. So when Component A living at Endpoint 1 wants to communicate with Component B living at Endpoint 2, so long as there is a mapping from 1 to 2, Camel will be able to transmit messages between these two.
Please stop me and correct me if I am wrong here!
So now, I've seen examples where it looks like routes can be configured in Java:
from("endpointA").routeId("someMessage").to("endpointB");
And I've seen examples where it looks like routes can be configured in XML:
<route id="">
<from .../>
<to .../>
</route>
Are these two methods for configuring routes, or are they different concepts altogether?
Finally, what is the format of the messages that can be routed between endpoints? If it has to be XML, for example, what is the XSD/schema of these routed messages? If it has to be a Java object, what bounds/restrictions apply to the objects that Camel can send?
It seems like you are getting a decent grasp of the concept.
I think it helps to think about endpoints in more abstract terms. The camel documentation is not much help here. Endpoints can be thought of as interfaces to a component. Each component can have 1 or more endpoints configured. It helps me to think about endpoints within the context of a route. A simple route can go from Endpoint A (This could be a JMS Queue, tcp socket, file or any camel component) and go to Endpoint B (which can be any camel component). You can of course have processors in the route too that transform the data.
The two examples of route creation you give are just that, two ways to create a route. They are the examples of the same concept. The first being Java DSL and the second using XML.
The format of the messages is typically XML, and the XML can be any valid XML and does not need to be tied to an XSD. The message can also be any Java object. As long as it is staying in the JVM (ie, not going over a socket) it doesn't need to be serializeable.
Route is an ordered combination of processing steps
Endpoint represents the beginning or end of a route (for the most part), that other routes might connect to as their beginning/end or might back onto an external system (e.g. JMS, email, etc.)
Related
I have a camel cxf-rs endpoint that splits the requests into two main parts.
form("cxfrs:bean:rsServer")
.when(isForward()).to("cxfrs:http://example.com")
.otherwise().process(myCustomDispatcher) // i want to get rid of this custom dispatcher
The first part is straight forwarded to a different service.
For the second part i would like to dispatch/call classes/methods that have jaxrs annotation. Currently i have a custom processor myCustomerDispatcher that duplicates the logic from the annotations and dispatches manually to classes and methods. Especially #Path and #PathParams are duplicated.
I tried:
to("bean:MyJaxRsImplemantion") this will work for beans with a single method matching the parameters in the camel exchange, but does not consider jax-rs annotations.
Serveral combinations with to("cxfrs:bean:cxfEndpoint?resourceClasses=MyJaxRsImplemantion"). it either requires a forwarding address, or acts on a new endpoint creating camel exchanges. I couldn't find a way to call the actual implementation.
The ProduceTemplates all seem to handle singular paths or situations.
Question:
How can i write a camel route that actually calls jax-rs resource methods without forwarding to a new service?
This is actually a really tough question. For one, even when you google it you don't get any straight answers. After an eternity of web surfing, it feels like it's the law of the land for camel routes to call jx-rs resource methods by forwarding to a new service.
And yes, it's almost like to("bean:MyJxRsImplemantion") is DESIGNED to ignore jax-rs annotations. So I've decided that it's impossible. Sorry.
I am trying to implement a Camel Component/Processor that takes one input and produces multiple output messages, similar to a Splitter. Like Splitter, the output should go to the next processor/endpoint in the route.
I have looked at Splitter & MulticastProcessor classes in the hope that I can reuse them or use similar logic. The idea, as I understood, is to create an new Exchange for each output and emit them. To do this, I need to provide the endpoint to which output is written to. This works, if I dynamically create the end point within the Processor class; my requirement is to send the output to the end point configured in the route. That is in the route below, mycomponent needs to write (multiple times) to file:output.
<route>
<from uri="file:input"/>
<to uri="mycomponent:OrderFlow?multi.output=true"/>
<to uri="file:output" />
</route>
In case of Splitter, it is instantiated by SplitDefinition class which has access to the output Processor/Endpoint.
a) From within a Processor is it possible to access the configured Output Processor/Endpoint?
b) If not, should I be writing a ProcessorDefinition class for my processor? Any pointers on this would help.
Two solutions suggested below by Petter are,
a) Inject a Producer template
b) Use Splitter component with a method call instead of writing a new component.
I assume you have read this page.
Yes, you can send multiple exchanges from a custom processor, but not really to the next processor in the flow. As in the link above, you can decouple the component implementation by injecting a producer template with a specific destination. You can cut your route into several parts using the direct or seda transport and make your component send the messages there. This way, you can reuse the code in several routes.
This is, as you point out, done in the splitter component (among others) in Camel core. Take a look at the multicastprocessor baseclass for example. However, there processors are aware of the following processors in the route, thanks to the route builder. You custom processor is not that lucky.
You can, non the less, extract that information from the CamelContext. Get hold of your route and there you can find the processors in the route. However, that seems like overcomplicating things.
UPDATE:
Instead of trying to alter the DSL, make use of the already existing DSL and components.
.split().method("mycomponent", "OrderFlow")
Instead of emitting new exchanges, your OrderFlow method just needs to create a List<..> with the resulting messages.
I'm trying to do a PoC in order to implement the pipes and filters eip pattern with Apache Camel.
From Camel documentation, I'm assuming that each filter must be implemented as an Endpoint ("With Camel you can split your processing across multiple independent Endpoint instances which can then be chained together.")
So, if I understood correctly, the Authenticate filter (from the example) must implement the Endpoint interface.
The "problem" is that I don't want to "re-invent the wheel". So instead of implementing the interface from the scratch, I'm almost sure that I can use an already implemented one. And the one is the BeanEndpoint.
Is that right?
I found a few examples of pipes and filters patterns (like this one) but none of then show how to implement the beans.
Can someone provide a bean implementation example?
TIA,
Bob
First of all, although I get where you're coming from when you say "camel implements filters as endpoints", I wouldn't strictly classify them as endpoints. More like message transformer/translators in my opinion.
So, in case you need to implement a custom filter as per your requirement, use the processor interface.
Basically, write a class(say, CustomProcessor) that implements Camel's Processor and write your custom filter strategy. Then, call it in your route as to("CustomProcessor").
The Processor page will surely clear all your concerns, so please have a look.
Also I assume you're aware of the camel message-filter pattern.
Thank you.
The Camel EIPs is listed here, and they all have examples and whatnot
http://camel.apache.org/eip
So for the pipes and filters you can find it on that link and see some examples
http://camel.apache.org/pipes-and-filters.html
And it seems you are new to Camel. Then I suggest to read this intro article to get your heads around Camel: http://java.dzone.com/articles/open-source-integration-apache
I'm trying to wrap my head around Apache Camel, and after spending some time this morning reading both the online Camel docs as well as the Javadocs, I have some questions that I can't seem to find answers for.
Is it true that all endpoints are either consumers or producers (or both)? Is it true that all processors are endpoints? Are there
any endpoints that are not processors?
What's the difference between a Message header and an Exchange? An exchange is considered to be a "message container", but how is that different from the metadata that a header would contain?
Is it typical to implement your own Message/Exchange? If so, what would be an example of doing so, and "straying" from the typical DefaultMessage and DefaultExchange?
Thanks in advance.
First things first: A good suggestion is to read the book Camel in Action, it explains most of the basic concepts. There is a free first chapter available online which explains the kind of questions you ask http://manning.com/ibsen/
An endpoint references a component and some component specific options, such as addresses etc. The endpoint can then (depending on the component) function as either consumer (ex. "servlet:path/to/web/service") or producer (ex. "http://localhost/path/to/web/service") or both of them (ex. "jms:queue:orderQueue").
There are headers in Camel messages as well. An exchange outlives an entire route, and exchange properties will also stay for the entire route. Message headers in Camel are a bit different concept. They are often closely mapped to the component used - i.e. a HTTP endpoint might set/change headers (for instance COOKIES etc.) while HTTP headers has no influence on exchange properties as these are for use within the camel route and camel logic only. The exchange also wrapps other non message specific things, such as exceptions.
It is quite uncommon to develop new message implementations. There could be a point in extending DefaultMessage when you have implemented your own component/protocol and need to keep instances of helper objects around in the message or whatnot. It's typically not done even when developing components. I have never heard of any custom implementation of an Exchange, and you should typically not do so without good reasons.
#DirtyMikeAndTheBoys you wrote:
Is it true that all processors are endpoints? Are there any endpoints
that are not processors?
This is not true. 'Processors' in Camel terminology are callbacks which are part of some pattern (like Aggregator, Message Channel or RoutingSlip). Processors receive the messages when they are flowing within a route and do something on messages. Messages are wrapped within Exchanges.
An Endpoint is where a route will receive messages (consumer endpoint) and where it will send the processed messages (To endpoint). So when you see the 'from' clause in a route, Camel engine is using a 'Consumer' instance associated with the endpoint instance defined in 'from' clause. It really depends on the endpoint implementation whether a new consumer instance is created/reused every where that given endpoint appears in a 'from' clause in your camel context.
Similarly when the same endpoint is mentioned in a 'To' clause, a Producer instance will be used (either created/reused) and will remain associated with the endpoint instance.
I am trying to set some headers on a message that is manipulated as it passes through the processors references in my camel DSL. The very first thing I have, however, is a processor for .onCompletion, which is supposed to read the message from the exchange, get the headers and log them.
Does that have to come last in my DSL? It appears that my finaly .process() processor can see all of the new header values I added through the rest of the code, but when I go to log them all at .onCompletion, the values for those headers is null. it's almost like it has a stale version of the message or exchange or something. Why else would this be happening?
Yes you should configure things like
onCompletion
onException
intercept
errorHandler
transacted
policy
etc
In the start of your route. However the DSL is Camel 2.x is very open, and thus you can in some places configure this elsewhere (eg not in the start). But the rule of thumb is to do this first. And then after that, you regular route.
Side note: Mind that Camel also allows you to configure these kind on global level (aka context scope) instead of route. Eg you can have
a context scoped error handler. And then only in a special route
override and have a route special error handler.
In Camel 3.0 onwards we will make the DSL more strict, so we enforce configuration in the start. This also reduces the number of methods you would see in the code assistance list (eg pressing ctrl + space) in the regular routes. As those configurations would then no longer be listed.
The reason why they show up, is that they inheirt the same base class which is the corner stone in the DSL. And we don't wanna break this in the current 2.x line as then some people may get affected.
the order shouldn't matter...it should be using a copy of the Exchange when the route has completed regardless...post your route and we can perhaps help more