Title: JNDIProject
<a name="JNDIProject-Overview"></a>
# JNDI

The Aries JNDI project aims to provide a fully compliant implementation of
the OSGi Alliance JNDI Service Specification. This specification details
how to advertise InitialContextFactory and ObjectFactories in an OSGi
environment. It also defines how to obtain services from the service
registry via JNDI.

<a name="JNDIProject-ServiceRegistryaccessfromJNDI"></a>
## Service Registry access from JNDI

The OSGi service registry provides a centralised register/query capability
for OSGi services. A common pattern outside of OSGi is to make use of the
JNDI API to access services from a directory system. The OSGi service
registry can be viewed as an example of such a system. The Aries JNDI
project provides two URL lookup mechanisms via JNDI that can be used to
access the service registry.

<a name="JNDIProject-osgi:service"></a>
## osgi:service

The osgi:service lookup scheme is defined by the JNDI Service Specification
and follows the scheme:


    osgi:service/<interface>[/<filter>](/<filter>.html)

The interface part is an interface name, like javax.sql.DataSource, or
javax.jms.ConnectionFactory. The filter allows selection based on the
properties of the service.

This example:

    Context ctx = new InitialContext();
    
    Runnable r = (Runnable)ctx.lookup("osgi:service/java.lang.Runnable");

is equivalent to this code written to the OSGi service registry API.

    BundleContext ctx = getABundleContext();
    ServiceReference ref = ctx.getServiceReference("java.lang.Runnable");
    if (ref != null) {
        Runnable r = ctx.getService(ref);
    }

Lets say you wanted to filter for a Runnable with a property called _fred_
which was mapped to _wilma_. You could write

    Context ctx = new InitialContext();
    
    Runnable r =
    (Runnable)ctx.lookup("osgi:service/java.lang.Runnable/(fred=wilma)");

which is equivalent to:

    BundleContext ctx = getABundleContext();
    ServiceReference[](.html)
     refs = ctx.getServiceReference("java.lang.Runnable", "(fred=wilma)");
    if (refs != null) {
      Runnable r = ctx.getService(refs[refs.length - 1](refs.length---1.html)
    );
}

The osgi:service namepsace returns proxies, so if the Runnable was
unregistered the proxy would switch to an equivalent alternative. If no
such alternative exists then an org.osgi.framework.ServiceException with a
type of ServiceException.UNREGISTERED.

<a name="JNDIProject-osgi:servicelist"></a>
## osgi:servicelist

It is possible that there are multiple services in the registry that match.
In this case the osgi:servicelist lookup scheme can be used. It has the
same format as osgi:service, but it is designed to return multiple.

<a name="JNDIProject-aries:services"></a>
## aries:services

The aries:services scheme works in the same way as the osgi:service scheme,
but does not perform proxying. You get the actual object back. Care must be
taken with this approach as the service could be unregistered, but the
client cannot tell to stop using it. As a result it should only be used if
the service is to be used for a short period of time. In addition their is
no way to indicate that the client is no longer using the service, so clean
up cannot occur.


<a name="JNDIProject-MoreInformation"></a>
## More Information


For more information, check out section "126 JNDI Services Specification
Version 1.0" in the "OSGi Service Platform Enterprise Specification,
Release 4, Version 4.2" available for public download from the [OSGi Alliance](http://www.osgi.org/Download/Release4V42)
.