I've read the https://camel.apache.org/threading-model.html document. It is not clear to me however whether a given route in one camel context uses a separate threadpool from a totally separate route in another camel context. Basically what I need to establish is whether by default multiple camel contexts you create, will use the/a same threadpool. Did I miss soemthing in the documentation?
No each thread-pool is private to each camel context. Unless you explicit setup a shared thread-pool and refer to use that pool in those Camel's. But a general rule of thumb, its all isolated per camel context.
Related
I'm new to Camel, and have some basic questions which can't found the answers online. Please help and I'm appreciate it.
I have read many example online, and saw bunch example like this:
from(direct:A).to(jms:queue:B)
But didn't see any configuration for them. My question is what will happen if the direct doesn't exist? How about from(jms:queue:A).to(direct:A)? and what about the other components?
For this example, what's the execution order? does it pass the original message to B first, then process and pass to C?
from(direct:A)
.to(jms:B)
.process(something)
.to(jms:C)
Direct is an in memory queue, provided by Camel. Prior it Camel 3, it was bundled with the camel-core module and you would not need any configuration at all in order to use the direct component. However, due to sake of modularity, since Camel 3, direct has been made its own component and in order to use it camel-direct needs to be imported.
Jms on the other hand is a generic component, using which you can implement connectivity to different Jms providers such as ActiveMq(though in Camel activemq has it's own component), IBM MQ, Weblogic JMS server, and others.
For your 1st question, if direct doesn't not exist, you need to import the direct component into your build. If the uri provided to the component is not present, Camel will create its own. This is true for most of the Camel components. One of the most common is the file component, which is used to pick up files from a given directory. If the given directory is not present, Camel is smart enough to create the directory. Obviously, these are default behaviours and you have a lot of control to pick and choose how you want your route to behave.
For your second question, the route will be processed entirely in order, which is, the message will be picked up from the direct:A, then will be sent to jms:B. After that it will be processed using the something processor and will finally be sent to jms:c.
The thing to note here is that the direct:A is just an example to show the syntax of a route. You can use any component which can act as a consumer.
I wanted to understand how multiple routes in same camel context will behave?
For example, Let's say I have an application wherein I have a single camel context which contains three different route builders each defining one route. Each of these routes are listening to different queues.
Can someone please let me know if all these three routes will work in parallel or only one will process the message while others wait?
I believe the queues will function in parallel. You can also specify the number of threads (.threads()) the route uses. So, with that it is safe to presume that the routes run in parallel.
I am working on an application that uses Apache Camel to flow a single request message (input) through some initial Camel components/logic and then to a multicast at which point the route branches out into multiple branches. The purpose of each branch is to retrieve data from a specific web service (or other back-end data source, e.g. database) and then after the web service invocation / data retrieval operation completes, each of the branches dumps its output data in the same way via a custom bean endpoint. I expect to eventually have approximately 40 different branches in the Camel route, each of which might flow through a different set of Camel components in order to prepare its request, submit the request, process the response, etc... I anticipate that a fair number of the branches will be quite similar (e.g. all SOAP invocations quite similar, all REST invocations quite similar, etc.) and so have concocted an approach whereby a config file stores the list of back-end data sources to be invoked/retrieved-from along with the ability to define (indirectly) the route that should be taken to reach each of those sources. The config file looks something like this:
[a]
route=X + Y
Y.url=http://someservice
[b]
route=Z
Z.someproperty=123
And then I have code that reads through that config file and treats each of the "sections" (e.g. "[a]", "[b]", etc.) as a branch (i.e. a destination out of the multicast) and relies on classes that are dynamically instantiated (e.g. XRouteSegment, YRouteSegment, ZRouteSegment) in order to each in-turn populate/define the route for its specific branch. As some examples, I have built RouteSegment helper classes for wiring up components such as Velocity, CXF, CXF-RS, for data marshalling/unmarshalling, etc... based on properties set in config file.
As far as initialization of the Camel context goes, it starts out in a fairly typical way with a single RouteBuilder which builds out the first part of the route up to the multicast. But then I go into a for loop and loop through all of the sources found in the config file (e.g. "a", "b", etc.) and create seda nodes for each of those which the multicast flows to. And then I call into each of the RouteSegment instances associated with a given source (e.g. X + Y) and allow those to add to the RouteDefinition as they need (e.g. from their seda start point going forward). And then back in my "main" RouteBuilder I tack on some final routing/components that is to be the same for all of the branches (i.e. the logic that forces each of the branches to store its data via the same custom bean).
The code works just fine, but I am questioning whether this approach is overkill and/or whether there is some easier/cleaner way of doing this that I am overlooking. Would I be better off just having individual Java classes (i.e. RouteBuilders) for each of the branches (in addition to the "trunk" and "tails" of the route)? What I was trying to avoid was having too much duplicated logic/code across all of those classes ... e.g. 20 classes all pulling data from SOAP web services in pretty much exactly the same way. So I am using a RouteSegment instance like "X" referenced above as re-usable shorthand for what would otherwise be a sequence of different Camel Java DSL calls (e.g. from/to/process/log/etc ... with parameters to control the specifics of the individual statements). Are there any other strategies/approaches I should consider in order to dynamically build out a Camel route (+ sizable number of branches) at runtime (e.g. within a for loop, or via some sort of reflection/discovery process (app runs using Spring Boot))?
Thanks in advance for any ideas you might be able to provide/suggest that I might not have thought of / tried yet!
I just want to throw in some subjects I am missing in your description.
If I understand your description correct, all your branches components that are called by multicast are not real components but kind of building blocks to build Camel routes at runtime. That sounds like they are not testable and not startable standalone (but perhaps you just not explained that aspect).
If you would build individual small components (every one with its own RouteBuilder) you would have something similar to a microservice architecture: small units to develop and deploy individually.
Since you use Spring Boot, you have autodiscovery of Routes, so they are kind of "pluggable". The components are also testable using Camel routetests etc.
The components would be much more "static" and small standalone projects. This also ensures a fast development roundtrip when you work on the components.
But as you write, this can lead to lots of redundant code. So I guess you have to decide what is more important for you.
For a project I need to have a unique ID generator. So I thought about a Singleton with synchronized methods.
Since a Singleton following the traditional Singleton pattern (private static instance) is shared accross Sessions, I'm wondering if the #Singleton Annotation is working the same way?
The documentation says: Identifies a type that the injector only instantiates once.
Does it mean, that a #Singleton will be independent per User Session (which is bad for an id-generator)? Should I prefer an old school Singleton with Class.getInstance() over an Injection of an #Singleton-Bean?
Or should I use neither nor and provide the Service within an #ApplicationScoped bean?
it musst be guaranteed that only ONE thread, independent of the user session can access the method to generate the next id. (It's not solvable with auto-increment database ids)
Edit: JSF 2.2, CDI and javax.inject.* i'm talking about :)
All those kinds of singletons (static, #javax.inject.Singleton, #javax.ejb.Singleton and #javax.enterprise.context.ApplicationScoped) are created once per JVM.
An object that is created once per user session must be annotated with #javax.enterprise.context.SessionScoped so no, singletons will not be instantiated per user session.
Notice that there are two #Singleton annotations, one in javax.inject and the other in the javax.ejb package. I'm referring to them by their fully-qualified names to avoid confusion.
The differences between all those singletons are subtle and I'm not sure I know all the implications, but a few come to mind:
#javax.ejb.Singleton is managed by the EJB container and so it can handle transactions (#javax.ejb.TransactionAttribute), read/write locking and time-outs (#javax.ejb.Lock, #javax.ejb.AccessTimeout), application startup (#javax.ejb.Startup, #javax.ejb.DependsOn) and so on.
#javax.enterprise.context.ApplicationScoped is managed by the CDI container, so you won't have the transaction and locking features that EJB has (unless you use a post-1.0 CDI that has added transactions), but you still have lots of nice things such as #javax.enterprise.inject.Produces, #javax.annotation.PostConstruct, #javax.inject.Named, #javax.enterprise.inject.Disposes (but many of these features are available to EJBs too).
#javax.inject.Singleton is similar to #ApplicationScoped, except that there is no proxy object (clients will have a reference to the object directly). There will be less indirection to reach the real object, but this might cause some issues related to serialization (see this: http://docs.jboss.org/weld/reference/latest-2.2/en-US/html_single/#_the_singleton_pseudo_scope)
A plain static field is simple and just works, but it's controlled by the class loader so in order to understand how/when they are instantiated and garbage collected (if ever), you will need to understand how class loaders work and how your application server manages its class loaders (when restarting, redeploying, etc.). See this question for more details.
javax.inject.Singleton - When used on your bean, you have to implement writeResolve() and readReplace to avoid any serialization issues. Use it judiciously based on what your bean actually has in it.
javax.enterprise.context.ApplicationScoped - Allows the container to proxy the bean and take care of serialization process automatically. This is recommended to avoid unprecedented issues.
For More information refer this page number 45.
I'm using servicemix and camel to publish to some activemq topics:
from("vm:all").recipientList().simple(String.format("activemq:topic:%s.%s.%s.%s.%s.%s","${header.type}", ...
but a new producer thread gets created per topic, any idea how I can control that?
Edit1:
Actually I realized that I was creating too many topics and should you Selectors instead: http://www.andrejkoelewijn.com/blog/2011/02/21/camel-activemq-topic-route-with-jms-selector/
Thanks for the help!
The typical scenario is that Camel is using JMSTemplate to fire messages to ActiveMQ. That means it creates a new producer each time. Actually, it creates a new connection, session and producer per message. That is usually no issue except performance wise.
This is typically handled by org.apache.activemq.pool.PooledConnectionFactory which caches connections, sessions and producers for you. However, depending on your configuration, it might create "some" producers initially, but they will be reused.
Check your Connection Factory settings in activemq-broker.xml and make sure you grab the PooledConnectionFactory.