93 lines
4.9 KiB
Markdown
93 lines
4.9 KiB
Markdown
Mbassador
|
|
=========
|
|
|
|
Mbassador is a very light-weight message bus (event bus) implementation following the publish subscribe pattern. It is designed
|
|
for ease of use and aims to be feature rich, extensible while preserving resource efficiency and performance.
|
|
Check out the <a href="http://codeblock.engio.net/?p=37" target="_blank">performance comparison</a> which also reviews part of the features of the compared implementations
|
|
|
|
At its core it offers the following:
|
|
|
|
+ <em><strong>Annotation driven</em></strong>: To define and customize a message handler simply mark it with @Listener annotation
|
|
+ <em><strong>Delivers everything</em></strong>: Messages must not implement any interface and can be of any type (-> message bus is typed using generics with upper
|
|
bound being Object.class). The class hierarchy of a message is considered during message delivery. This means that listeners will also receive
|
|
subtypes of the message type they are listening for, e.g. a listener for Object.class receives everything.
|
|
+ <em><strong>Synchronous and asynchronous message delivery</em></strong>: A handler can be invoked to handle a message either synchronously or
|
|
asynchronously. This is configurable for each handler via annotations. Message publication itself supports synchronous (method
|
|
blocks until messages are delivered to all handlers) or asynchronous (fire and forget) dispatch
|
|
+ <em><strong>Weak references</em></strong>: Mbassador uses weak references to all listening objects to relieve the programmer of the burden to explicitly unregister
|
|
listeners that are not used anymore (of course it is also possible to explicitly unregister a listener if needed). This is very comfortable
|
|
in certain environments where objects are created by frameworks, i.e. spring, guice etc. Just stuff everything into the message bus, it will
|
|
ignore objects without message handlers and automatically clean-up orphaned weak references after the garbage collector has done its job.
|
|
+ <em><strong>Filtering</em></strong>: Mbassador offers static message filtering. Filters are configured using annotations and multiple filters can be attached to
|
|
a single message handler
|
|
+ <em><strong>Handler priorities</em></strong>: A listener can be associated with a priority to influence the order of the message delivery
|
|
+ <em><strong>Error handling</em></strong>: Errors during message delivery are sent to an error handler of which a custom implementation can easily be plugged-in.
|
|
+ <em><strong>Ease of Use</em></strong>: Using Mbassador in your project is very easy. Create as many instances of Mbassador as you like (usually a singleton will do),
|
|
mark and configure your message handlers with @Listener annotations and finally register the listeners at any Mbassador instance. Start
|
|
sending messages to your listeners using one of Mbassador's publication methods (sync or async). Done!
|
|
|
|
|
|
|
|
<h2>Usage</h2>
|
|
|
|
Listener definition (in any bean):
|
|
|
|
// every event of type TestEvent or any subtype will be delivered
|
|
// to this handler
|
|
@Listener
|
|
public void handleTestEvent(TestEvent event) {
|
|
// do something
|
|
}
|
|
|
|
// this handler will be invoked asynchronously
|
|
@Listener(dispatch = Mode.Asynchronous)
|
|
public void handleSubTestEvent(SubTestEvent event) {
|
|
// do something more expensive here
|
|
}
|
|
|
|
// this handler will receive events of type SubTestEvent
|
|
// or any subtabe and that passes the given filter(s)
|
|
@Listener(priority = 10,
|
|
dispatch = Mode.Synchronous,
|
|
filters = {@Filter(MessageFilter.None.class),@Filter(MessageFilter.All.class)})
|
|
public void handleFiltered(SubTestEvent event) {
|
|
//do something special here
|
|
}
|
|
|
|
Creation of message bus and registration of listeners:
|
|
|
|
// create as many instances as necessary
|
|
// bind it to any upper bound
|
|
MBassador<TestEvent> bus = new MBassador<TestEvent>();
|
|
ListeningBean listener = new ListeningBean();
|
|
// the listener will be registered using a weak-reference
|
|
bus.subscribe(listener);
|
|
// objects without handlers will be ignored
|
|
bus.subscribe(new ClassWithoutAnyDefinedHandlers());
|
|
|
|
|
|
Message publication:
|
|
|
|
TestEvent event = new TestEvent();
|
|
TestEvent subEvent = new SubTestEvent();
|
|
|
|
bus.publishAsync(event); //returns immediately, publication will continue asynchronously
|
|
bus.post(event).asynchronously(); // same as above
|
|
bus.publish(subEvent); // will return after each handler has been invoked
|
|
bus.post(subEvent).now(); // same as above
|
|
|
|
|
|
<h2>Planned features</h2>
|
|
|
|
+ Maven dependency: Add Mbassador to your project using maven. Coming soon!
|
|
+ Spring integration with support for conditional message dispatch in transactional context (dispatch only after
|
|
successful commit etc.)
|
|
|
|
<h2>License</h2>
|
|
|
|
This project is distributed under the terms of the MIT License. See file "LICENSE" for further reference.
|
|
|
|
|
|
|
|
|