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Table of Contents
The RMI registry service provider allows JNDI applications to access
remote objects registered with the RMI registry. Given the location
of a registry, the provider will create a naming context with bindings
for the objects registered there. Such a context may be bound into
another JNDI-accessible namespace (such as LDAP, for example).
References to individual remote objects may likewise be bound into
another namespace.
A key benefit of binding registry contexts into other namespaces is
location-independent access to remote objects: the RMI clients do not
need to know the registry's host name or port number. RMI servers can
take advantage of this to advertise their services to potential
clients. In addition, remote objects can be linked into the same
enterprise directory that is used to access information about people,
organizations, and network resources.
With this service provider installed, JNDI subsumes the functionality
of the java.rmi.Naming class.
This document describes the features of the RMI registry service provider.
The following JNDI environment properties are used by the RMI registry
service provider.
See the
JNDI
documentation
for a
description of how properties are initialized using the environment
properties, system properties, applet parameters, and resource files.
For example:
This property is used in conjunction with the
java.naming.provider.url property.
This property must be set if you are using the
registry as the initial context. The only exception is
if you supply only URLs to the initial context, in which case,
you don't need to specify this property. See
RMI URLs for details.
For example:
The default value of this property is "rmi:", signifying a registry
running on port 1099 of the local host.
This property is used in conjunction with the
java.naming.factory.initial property.
The RMI registry supports a flat namespace. Since there is no
hierarchy, every name is atomic. Each name may be composed of any
characters, and case is significant.
Names are passed as arguments to the methods of a registry context,
and are returned as the results of those methods, either as
Name
objects or as strings. When a Name object is used, it should have a
single component whose value is the atomic name that will be passed on
to the registry. When a string is used as a name, it is interpreted
as the string representation of a composite name. So if ctx is a
registry context, for example, then the following two unbind
operations are equivalent:
JNDI provides support for resolving URLs that name objects. The
registry service provider allows RMI URLs to be used as names in this
manner. This provides a generalization of the java.rmi.Naming
functionality, only using the more general JNDI interface.
The class com.sun.jndi.url.rmi.rmiURLContextFactory implements
a URL context factory for RMI URLs. This allows an RMI URL to be passed
as a name to the default JNDI initial context.
The format of an RMI URL is one of the following:
If the host is omitted, the local host is assumed. If the port
is omitted, the default registry port 1099 is assumed.
The registry service provider implements the java.naming.Context and
java.naming.Referenceable
interfaces. Context and Referenceable methods are
mapped onto registry operations as described below.
Binding Objects into the Registry
An object may be bound into a registry context if it implements the
java.rmi.Remote interface. An object may also be bound if it is
a JNDI Reference object, or if it implements the Referenceable
interface (in which case the corresponding reference will be bound in
place of the object itself).
Binding Registry Contexts and Remote Objects
Each RMI registry context implements the Referenceable interface.
It may therefore be bound into any JNDI-accessible namespace that can
store Referenceable objects. A reference to an individual remote
object that is registered with a registry may also be constructed,
allowing that object to be bound into another namespace.
The class com.sun.jndi.rmi.registry.RegistryContextFactory
implements the object factory that converts registry references into the
corresponding registry contexts or remote objects.
For a registry context to be constructed, the registry's URL must be
determined. This URL may come from the
java.naming.provider.url property, or may be passed as a name
to the initial context, or may be embedded in a registry reference. If
the URL contains no host name or uses the host name "localhost", then the
registry context's getReference() method is unable to return a
reference for the context. Such a registry context, therefore, cannot be
bound into another namespace.
Registry Reference Format
A JNDI reference for an RMI registry contains
a list of string addresses (class StringRefAddr), each
tagged with the type "URL". Each address contains an RMI URL locating
either a registry, or a remote object registered with a registry
(see RMI URL Format above).
When multiple URLs appear within a single reference, each
represents an alternative address for the same logical resource. The
order of the addresses is not significant. Addresses not of class
StringRefAddr, or not of address type "URL", are ignored.
Example 1
To create an initial context that accesses a registry, set the
properties java.naming.factory.initial and
java.naming.provider.url as described in
Environment Properties above. Then the names stored
in the registry, for example, may be listed as follows:
Example 2
Instead of using the properties as above, you may pass an RMI URL
as a name to resolve in the default initial context:
Example 3
A registry context may be bound into another JNDI-accessible
namespace. To bind registryCtx (from the preceding example) into an
LDAP directory, for example:
Example 4
A remote object that is registered with an RMI registry may be
bound into another JNDI-accessible namespace by constructing a
reference for that object. If the variable obj holds the object
named R1 from the preceding examples, it may be bound into an LDAP
directory as follows:
The usual security considerations of RMI apply. For RMI to
dynamically load classes from a remote server, a security manager must
first be installed. This can be done in the same way as it would for
any other RMI application. See the
JavaTM Remote Method Invocation Specification. Or, if the
environment property java.naming.rmi.security.manager is passed
to the provider, then the provider will attempt to install the
RMISecurityManager itself.
The application using JNDI and the RMI registry provider must be
granted the following permissions:
Introduction
Environment Properties
This property is used to select the registry service provider as
the initial context. It is not used by the provider itself.
It specifies the class name of the initial context factory for
the provider.
env.put(Context.INITIAL_CONTEXT_FACTORY,
"com.sun.jndi.rmi.registry.RegistryContextFactory");
java.naming.provider.url
This property specifies the location of the registry when the
registry is being used as the initial context. It's value is an
RMI URL with no object name component
(see RMI URL Format below).
env.put(Context.PROVIDER_URL, "rmi://server:1099");
java.naming.factory.state
A colon-separated list of the fully qualified class names
of state factory classes used to get an object's state for storing
given the object itself. You can use this mechanism to transform
an object into forms that can be stored into the registry.
The RMI registry service provider supports storing java.rmi.Remote,
javax.naming.Reference, and javax.naming.Referenceable objects.
See
javax.naming.spi.NamingManager.getStateToBind() for details.
java.naming.factory.object
A colon-separated list of the fully qualified class names
of object factory classes for transforming objects read from the registry.
You can use this mechanism to transform an object into forms expected
by the application. See
javax.naming.spi.NamingManager.getObjectInstance() for details.
java.naming.rmi.security.manager
This property, when set to any value, indicates that the provider
should attempt to install the RMISecurityManager. See the
Security Considerations section below.
Names
Care must be taken with names containing any of the four
meta-characters that are treated specially during the parsing of
composite names: '/', '\\', '"', and '\''. These characters must
be properly escaped or quoted. The atomic name X/Y, for example,
may be represented as the composite name X\/Y so as not to be
mistaken for a two-component name with X and Y as its components.
See CompositeName for more information.
String name = ...
ctx.unbind(name);
ctx.unbind(new CompositeName(name));
RMI URLs
RMI URL Format
rmi://[host][:port][/[object]]
rmi:[/][object]
If the object name is absent, then the URL names the registry at the
given host and port. Otherwise, it names the remote object registered
at that registry under the name provided.
API Mapping
lookup()
lookupLink()
The java.rmi.Registry.lookup() method is called. If the returned
object is a wrapper around a javax.naming.Reference,
the referenced object is
created using javax.naming.spi.NamingManager.getObjectInstance().
JNDI links
are not currently supported.
bind()
The java.rmi.Registry.bind() method is called. State factories are
first consulted through javax.naming.spi.NamingManager.getStateToBind(). The
object being bound must be of type java.rmi.Remote,
javax.naming.Reference, or javax.naming.Referenceable.
If the object is a
javax.naming.Reference or javax.naming.Referenceable,
its reference is wrapped in a Remote wrapper and then bound
(see Binding Objects into the Registry below).
rebind()
The java.rmi.Registry.rebind() method is called. Objects are
otherwise treated as for the JNDI bind() operation.
unbind()
The java.rmi.Registry.unbind() method is called.
rename()
This method is implemented as a sequence of JNDI operations:
lookup(), bind(), unbind(). The sequence
is not performed atomically.
list()
The java.rmi.Registry.list() method is called. As this provides no
information about the types of the bound objects, each
javax.naming.NameClassPair returned has the generic
java.lang.Object as its class name.
listBindings()
The java.rmi.Registry.list() method is called. As each
javax.naming.Binding is read from the resulting enumeration,
java.rmi.Registry.lookup() is called and passed through
javax.naming.spi.NamingManager.getObjectInstance().
createSubcontext()
destroySubcontext()
These operations are not supported.
getNameParser()
Returns a name parser for case-sensitive atomic names.
getNameInNamespace()
Returns the empty string (the name of the registry).
composeName()
Returns the composition of the two names.
addToEnvironment()
The specified property is added to the context's environment.
If the java.naming.rmi.security.manager property is added,
the provider will attempt to install the default RMI security manager
(see Security Considerations). Other properties may be
added or changed in the environment, but have no additional effect on
the context.
removeFromEnvironment()
The specified property is removed from the context's environment.
The context is otherwise unaffected.
close()
Clears internal state used by the provider, but otherwise has
no immediate effect.
getReference()
If this context was constructed from a reference, a clone of
that reference is returned. Otherwise a new reference for the
context is returned, providing that the host name can be
determined and is not "localhost"
(see Binding Registry Contexts and Remote Objects
below).
Bindings
Usage Examples
Context ictx = new InitialContext(env);
NamingEnumeration enum = ictx.list("");
Context registryCtx = (Context)ictx.lookup("rmi://host");
If the names R1 and R2 are bound in this registry, then a JNDI
client browsing the LDAP namespace will see R1 and R2 beneath the
cn=rmi entry.
Context ldapCtx = (Context)ictx.lookup("ldap://server/o=sun,c=us");
ldapCtx.bind("cn=rmi", registryCtx);
RefAddr addr = new StringRefAddr("URL", "rmi://host/R1");
Reference ref = new Reference(obj.getClass().getName(), addr);
ldapCtx.bind("cn=R1", ref);
Security Considerations
Security Manager
Permissions
permission java.net.SocketPermission "host[:port]", "connect";
For each host/port identified in the java.naming.provider.url
property and in URL string names supplied to context methods.
permission java.net.SocketPermission "host[:port]", "connect,accept";
For each host/port identified in the URL strings in
javax.naming.References.
permission java.lang.RuntimePermission "setSecurityManager";
If using the java.naming.rmi.security.manager environment
property, which asks the RMI registry provider to install the
RMISecurityManager.
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