Eclipse Communication Framework
ECF Documentation
| ECF Documentation | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Note: standalone bookmark for the ECF API (javadocs) web pages. Copy and paste: http://www.eclipse.org/ecf/org.eclipse.ecf.docs/api |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Introduction: ECF Containers | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ECF introduces the concept of a communications container. ECF containers represent access to
a protocol-specific communications context. For connection-oriented communications, an ECF container loosely
corresponds to the traditional notion of a communications session, but the more general container concept is also
useful for capturing context even if the communications are not session-oriented.
ECF containers can represent both point-to-point communications (e.g. client/server) or
publish-and-subscribe (group) communications. Container instances can provide access to synchronous
communications only, asynchronous communications only, or both together. This flexibility allows
many communications applications to be constructed out of one or more ECF containers...each of which
provides access to some specific communications context and some protocol(s) for communicating within
that context.
Instance CreationContainer instance creation is done via ECF-provided factory APIs. For example, here's code to create and IContainer instance:
IContainer container = getContainerFactory().createContainer(<Container Type>);
Note that the getContainerFactory() method should return an IContainerFactory instance and this can be accessed as a singleton OSGi Service (via OSGi ServiceReferece, ServiceTracker or Declarative Services).
Once constructed, IContainer instances may be used in the manner appropriate for the given application.
Container Types Available at dev.eclipse.org
Container Types Available at ECF Github site
Container Instance DisposalWhen no longer required the IContainer.dispose() method should be called to release any resources associated with the container instance upon its construction or used during its lifecycle (e.g. network resources, etc).Connection/DisconnectionThe IContainer interface exposes two key methods: connect(ID targetID, IConnectContext connectContext) and disconnect(). As is obvious, these two methods allow container implementations to initiate communication with remote services, either server-based or group-based communications. Notice the first parameter to the connect method...targetID. TargetID is of type ID. The targetID parameter identifies the target server or group for the connect operation. It is of type ID so that the to allow the target communications service to be of many kinds...e.g. client-server or peer-to-peer. For example, for http communication the targetID would consist of the URL specifying a particular file at a particular path on a particular server...e.g: http://www.eclipse.org/ecf. For some other communications protocol the ID provided would be different...e.g: sip:someone@example.com;transport=tcp. All such targets for connect may be represented via an instance of the ID interface.Example Code: Container Creation and ConnectionHere's an example code snippet that shows the creation and connection of an ECF container:
// make container instance
IContainer cont = getContainerFactory().createContainer("ecf.generic.client");
// make targetID
ID targetID = IDFactory.getDefault().createID(cont.getConnectNamespace(),"ecftcp://foo.com:3282/server");
// then connect to targetID with null authentication data
cont.connect(targetID,null);
Namespaces and ID ConstructionThe org.eclipse.ecf core plugin defines a namespace extension point, so that ECF provider plugins can provide their own Namespace implementations. For example, here is the namespace extension definition for the org.eclipse.ecf.provider.xmpp plugin:
<extension point="org.eclipse.ecf.namespace">
<namespace
class="org.eclipse.ecf.provider.xmpp.identity.XMPPNamespace"
description="XMPP Namespace"
name="ecf.xmpp"/>
</extension>
This assigns the name "ecf.xmpp" to the class org.eclipse.ecf.provider.xmpp.identity.XMPPNamespace. Notice that this
class must be a subclass of org.eclipse.ecf.core.identity.Namespace.
The XMPPNamespace class provides the
XMPP namespace implementation and as described above implements the XMPP namespace restrictions. It is also responsible for
constructing new ID instances via the ECF IDFactory.
For example, to construct an instance of and XMPP ID, a client could use the following code:
ID newID = IDFactory.getDefault().createID("ecf.xmpp","slewis@foo.com");
Underneath the covers of the IDFactory.createID method the following occurs:
Container Extensibility through AdaptersTo support run-time extensibility, the IContainer interface inherits from org.eclipse.core.runtime.IAdaptable. This interface exposes a single method: the 'getAdapter(Class intf)' method. In the case of IContainer instances, this allows client applications to query the IContainer instance at runtime about it's exposed capabilities, and get access to those capabilities if they are available. So, for example, perhaps we're interested in creating an instant messaging application and wish to use the capabilities exposed by the IPresenceContainer interface. To do this, we simply query the IContainer instance at runtime to see if it provides access to IPresenceContainer capabilities:
IPresenceContainer pc = (IPresenceContainer) cont.getAdapter(IPresenceContainer.class);
if (pc != null) {
// The container DOES expose IPresenceContainer capabilities, so we can use them!
} else {
// The container does not expose IPresenceContainer capabilities...we're out of luck
}
Among other positive characteristics, this adapter mechanism provides a consistent-yet-simple way for
a wide variety of container types to be defined and used without the need to update the ECF
IContainer abstractions.
See the documentation for the IContainer.getAdapter() method.
See also a terrific article on EclipseZone about usage of IAdaptable for runtime extensibility
IdentityIn ECF, identity of local or remote entities such as users, remote services, and groups are all represented via the ID interface. This interface provides the basic contract for addressing uniquely identified entities. ID instances belong to a given Namespace Namespaces define the range of allowable values of the ID instances belonging to that Namespace. So, for example, the Namespace of XMPP (Jabber) user identities is defined by XMPP RFC3920 as having the following structure
jid = [ node "@" ] domain [ "/" resource ]
domain = fqdn / address-literal
fqdn = (sub-domain 1*("." sub-domain))
sub-domain = (internationalized domain label)
address-literal = IPv4address / IPv6address
example = slewis@foo.com/ecf
The ECF XMPP provider implementation restricts jids to this syntax by providing a Namespace subclass responsible
for constructing ID instances that follow the rules defined by the protocol specification. Other communications protocols
and their associated service identities have
their own Namespaces (e.g. ftp, http, sip, irc, etc, etc), each with it's own requirements for addressing and
identity. The ID
contract is not bound to any specific protocol, and makes it possible to create client applications that are
insensitive to the addressing differences between protocols while still guaranteeing basic uniqueness requirements within a given namespace.
Example: Container creation, ID creation, container adapter, and connection
// Create the new container
IContainer client = ContainerFactory
.getDefault().createContainer(containerType);
// Create the targetID
ID targetID = IDFactory.getDefault().createID(client.getConnectNamespace(), uri);
// Check for IPresenceContainer....if it is, setup presence UI, if not setup shared object container
IPresenceContainer pc = (IPresenceContainer) client
.getAdapter(IPresenceContainer.class);
if (pc != null) {
// Setup presence UI
presenceContainerUI = new PresenceContainerUI(pc);
presenceContainerUI.setup(client, targetID, username);
} else throw new NullPointerException("IPresenceContainer interface not exposed by client with type "+containerType);
// connect
client.connect(targetID, getJoinContext(username, connectData));
UNDER CONSTRUCTION 6/17/07
back to top |