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<html>
<head>
<title>RMI connector</title>
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<p>The RMI connector is a connector for the JMX Remote API that
uses RMI to transmit client requests to a remote MBean server.
This package defines the classes that the user of an RMI
connector needs to reference directly, for both the client and
server sides. It also defines certain classes that the user
will not usually reference directly, but that must be defined so
that different implementations of the RMI connector can
interoperate.</p>
<p>The RMI connector supports both the JRMP and the IIOP transports
for RMI.</p>
<p>Like most connectors in the JMX Remote API, an RMI connector
usually has an address, which
is a {@link javax.management.remote.JMXServiceURL
JMXServiceURL}. The protocol part of this address is
<code>rmi</code> for a connector that uses the default RMI
transport (JRMP), or <code>iiop</code> for a connector that
uses RMI/IIOP.</p>
<p>There are two forms for RMI connector addresses:</p>
<ul>
<li>
In the <em>JNDI form</em>, the URL indicates <em>where to find
an RMI stub for the connector</em>. This RMI stub is a Java
object of type {@link javax.management.remote.rmi.RMIServer
RMIServer} that gives remote access to the connector server.
With this address form, the RMI stub is obtained from an
external directory entry included in the URL. An external
directory is any directory recognized by {@link javax.naming
JNDI}, typically the RMI registry, LDAP, or COS Naming.
<li>
In the <em>encoded form</em>, the URL directly includes the
information needed to connect to the connector server. When
using RMI/JRMP, the encoded form is the serialized RMI stub
for the server object, encoded using BASE64 without embedded
newlines. When using RMI/IIOP, the encoded form is the CORBA
IOR for the server object.
</ul>
<p>Addresses are covered in more detail below.</p>
<h3>Creating an RMI connector server</h3>
<p>The usual way to create an RMI connector server is to supply an
RMI connector address to the method {@link
javax.management.remote.JMXConnectorServerFactory#newJMXConnectorServer
JMXConnectorServerFactory.newJMXConnectorServer}. The MBean
server to which the connector server is attached can be
specified as a parameter to that method. Alternatively, the
connector server can be registered as an MBean in that MBean
server.</p>
<p>An RMI connector server can also be created by constructing an
instance of {@link
javax.management.remote.rmi.RMIConnectorServer
RMIConnectorServer}, explicitly or through the MBean server's
<code>createMBean</code> method.</p>
<h4>Choosing the RMI transport</h4>
<p>You can choose the RMI transport (JRMP or IIOP) by specifying
<code>rmi</code> or <code>iiop</code> in the
<code><em>protocol</em></code> part of the
<code>serviceURL</code> when creating the connector server. You
can also create specialised connector servers by instantiating
an appropriate subclass of {@link
javax.management.remote.rmi.RMIServerImpl RMIServerImpl} and
supplying it to the <code>RMIConnectorServer</code>
constructor.</p>
<h4><a name="servergen">Connector addresses generated by the
server</a></h4>
<p>If the <code>serviceURL</code> you specify has an empty URL
path (after the optional host and port), or if you do not
specify a <code>serviceURL</code>, then the connector server
will fabricate a new <code>JMXServiceURL</code> that clients can
use to connect:</p>
<ul>
<li><p>If the <code>serviceURL</code> looks like:</p>
<pre>
<code>service:jmx:rmi://<em>host</em>:<em>port</em></code>
</pre>
<p>then the connector server will generate an {@link
javax.management.remote.rmi.RMIJRMPServerImpl
RMIJRMPServerImpl} and the returned <code>JMXServiceURL</code>
looks like:</p>
<pre>
<code>service:jmx:rmi://<em>host</em>:<em>port</em>/stub/<em>XXXX</em></code>
</pre>
<p>where <code><em>XXXX</em></code> is the serialized form of the
stub for the generated object, encoded in BASE64 without
newlines.</p>
<li><p>If the <code>serviceURL</code> looks like:</p>
<pre>
<code>service:jmx:iiop://<em>host</em>:<em>port</em></code>
</pre>
<p>then the connector server will generate an {@link
javax.management.remote.rmi.RMIIIOPServerImpl
RMIIIOPServerImpl} and the returned
<code>JMXServiceURL</code> looks like:</p>
<pre>
<code>service:jmx:iiop://<em>host</em>:<em>port</em>/ior/IOR:<em>XXXX</em></code>
</pre>
<p>where <code>IOR:<em>XXXX</em></code> is the standard CORBA
encoding of the Interoperable Object Reference for the
generated object.</p>
<li><p>If there is no <code>serviceURL</code>, there must be a
user-provided <code>RMIServerImpl</code>. If the {@link
javax.management.remote.rmi.RMIServerImpl#toStub toStub}
method on this object returns an instance of {@link
javax.rmi.CORBA.Stub}, then the connector server will generate
a <code>JMXServiceURL</code> using the <code>iiop</code>
form above. Otherwise, it will generate a
<code>JMXServiceURL</code> using the <code>rmi</code>
form.</p>
</ul>
<p>The <code><em>host</em></code> in a user-provided
<code>serviceURL</code> is optional. If present, it is copied
into the generated <code>JMXServiceURL</code> but otherwise
ignored. If absent, the generated <code>JXMServiceURL</code>
will have the local host name.</p>
<p>The <code><em>port</em></code> in a user-provided
<code>serviceURL</code> is also optional. If present, it is
also copied into the generated <code>JMXServiceURL</code>;
otherwise, the generated <code>JMXServiceURL</code> has no port.
For an <code>serviceURL</code> using the <code>rmi</code>
protocol, the <code><em>port</em></code>, if present, indicates
what port the generated remote object should be exported on. It
has no other effect.</p>
<p>If the user provides an <code>RMIServerImpl</code> rather than a
<code>JMXServiceURL</code>, then the generated
<code>JMXServiceURL</code> will have the local host name in its
<code><em>host</em></code> part and no
<code><em>port</em></code>.</p>
<h4><a name="directory">Connector addresses based on directory
entries</a></h4>
<p>As an alternative to the generated addresses just described,
the <code>serviceURL</code> address supplied when creating a
connector server can specify a <em>directory address</em> in
which to store the provided or generated <code>RMIServer</code>
stub. This directory address is then used by both client and
server.</p>
<p>In this case, the <code>serviceURL</code> has one of these two
forms:</p>
<pre>
<code>service:jmx:rmi://<em>host</em>:<em>port</em>/jndi/<em>jndi-name</em></code>
<code>service:jmx:iiop://<em>host</em>:<em>port</em>/jndi/<em>jndi-name</em></code>
</pre>
<p>Here, <code><em>jndi-name</em></code> is a string that can be
supplied to {@link javax.naming.InitialContext#bind
javax.naming.InitialContext.bind}.</p>
<p>As usual, the <code><em>host</em></code> and
<code>:<em>port</em></code> can be omitted.</p>
<p>The connector server will generate an
<code>RMIServerImpl</code> based on the protocol
(<code>rmi</code> or <code>iiop</code>) and, for
<code>rmi</code>, the <code><em>port</em></code> if any. When
the connector server is started, it will derive a stub from this
object using its {@link
javax.management.remote.rmi.RMIServerImpl#toStub toStub} method
and store the object using the given
<code><em>jndi-name</em></code>. The properties defined by the
JNDI API are consulted as usual.</p>
<p>For example, if the <code>JMXServiceURL</code> is:
<pre>
<code>service:jmx:rmi://ignoredhost/jndi/rmi://myhost/myname</code>
</pre>
then the connector server will generate an
<code>RMIJRMPServerImpl</code> and store its stub using the JNDI
name
<pre>
<code>rmi://myhost/myname</code>
</pre>
which means entry <code>myname</code> in the RMI registry
running on the default port of host <code>myhost</code>. Note
that the RMI registry only allows registration from the local
host. So, in this case, <code>myhost</code> must be the name
(or a name) of the host that the connector server is running
on.</p>
<p>In this <code>JMXServiceURL</code>, the first <code>rmi:</code>
specifies the RMI
connector, while the second <code>rmi:</code> specifies the RMI
registry.</p>
<p>As another example, if the <code>JMXServiceURL</code> is:
<pre>
<code>service:jmx:iiop://ignoredhost/jndi/ldap://dirhost:9999/cn=this,ou=that</code>
</pre>
then the connector server will generate an
<code>RMIIIOPServerImpl</code> and store its stub using the JNDI
name
<pre>
<code>ldap://dirhost:9999/cn=this,ou=that</code>
</pre>
which means entry <code>cn=this,ou=that</code> in the LDAP
directory running on port 9999 of host <code>dirhost</code>.</p>
<p>If the <code>JMXServiceURL</code> is:
<pre>
<code>service:jmx:iiop://ignoredhost/jndi/cn=this,ou=that</code>
</pre>
then the connector server will generate an
<code>RMIIIOPServerImpl</code> and store its stub using the JNDI
name
<pre>
<code>cn=this,ou=that</code>
</pre>
For this case to work, the JNDI API must have been configured
appropriately to supply the information about what directory to
use.</p>
<p>In these examples, the host name <code>ignoredhost</code> is
not used by the connector server or its clients. It can be
omitted, for example:</p>
<pre>
<code>service:jmx:iiop:///jndi/cn=this,ou=that</code>
</pre>
<p>However, it is good practice to use the name of the host
where the connector server is running. This is often different
from the name of the directory host.</p>
<h4>Connector server attributes</h4>
<p>When using the default JRMP transport, RMI socket factories can
be specified using the attributes
<code>jmx.remote.rmi.client.socket.factory</code> and
<code>jmx.remote.rmi.server.socket.factory</code> in the
<code>environment</code> given to the
<code>RMIConnectorServer</code> constructor. The values of these
attributes must be of type {@link
java.rmi.server.RMIClientSocketFactory} and {@link
java.rmi.server.RMIServerSocketFactory}, respectively. These
factories are used when creating the RMI objects associated with
the connector.</p>
<h3>Creating an RMI connector client</h3>
<p>An RMI connector client is usually constructed using {@link
javax.management.remote.JMXConnectorFactory}, with a
<code>JMXServiceURL</code> that has <code>rmi</code> or
<code>iiop</code> as its protocol.</p>
<p>If the <code>JMXServiceURL</code> was generated by the server,
as described above under <a href="#servergen">"connector
addresses generated by the server"</a>, then the client will
need to obtain it directly or indirectly from the server.
Typically, the server makes the <code>JMXServiceURL</code>
available by storing it in a file or a lookup service.</p>
<p>If the <code>JMXServiceURL</code> uses the directory syntax, as
described above under <a href="#directory">"connector addresses
based on directory entries"</a>, then the client may obtain it
as just explained, or client and server may both know the
appropriate directory entry to use. For example, if the
connector server for the Whatsit agent uses the entry
<code>whatsit-agent-connector</code> in the RMI registry on host
<code>myhost</code>, then client and server can both know
that the appropriate <code>JMXServiceURL</code> is:</p>
<pre>
<code>service:jmx:rmi:///jndi/rmi://myhost/whatsit-agent-connector</code>
</pre>
<p>If you have an RMI stub of type {@link
javax.management.remote.rmi.RMIServer RMIServer}, you can
construct an RMI connection directly by using the appropriate
constructor of {@link javax.management.remote.rmi.RMIConnector
RMIConnector}.</p>
<h3>Specifying an ORB for the RMI/IIOP connector</h3>
<p>When using the IIOP transport, the client and server can
specify what ORB to use
with the attribute <code>java.naming.corba.orb</code>.
Connection to the ORB happens at {@link
javax.management.remote.rmi.RMIConnectorServer#start() start} time
for the connector server, and at {@link
javax.management.remote.rmi.RMIConnector#connect(java.util.Map)
connect} time for the connector client.
If the <code>java.naming.corba.orb</code> attribute is contained
in the environment Map, then its value (an {@link
org.omg.CORBA.ORB ORB}), is used to connect the IIOP Stubs.
Otherwise, a new org.omg.CORBA.ORB is created by calling {@link
org.omg.CORBA.ORB
org.omg.CORBA.ORB.init((String[])null,(Properties)null)}. A
later RMI connector client or server in the same JVM can reuse
this ORB, or it can create another one in the same way.</p>
<p>If the <code>java.naming.corba.orb</code> attribute is
specified and does not point to an {@link org.omg.CORBA.ORB ORB},
then an <code>{@link java.lang.IllegalArgumentException}</code>
will be thrown.</p>
<p>The mechanism described here does not apply when the IIOP
Remote objects (Stubs or Servers) are created and connected to
an ORB manually before being passed to the RMIConnector and
RMIConnectorServer.</p>
<h3>Dynamic code downloading</h3>
<p>If an RMI connector client or server receives from its peer an
instance of a class that it does not know, and if dynamic code
downloading is active for the RMI connection, then the class can
be downloaded from a codebase specified by the peer. The
article <a
href="{@docRoot}/../technotes/guides/rmi/codebase.html"><em>Dynamic
code downloading using Java RMI</em></a> explains this in more
detail.</p>
@see <a href="{@docRoot}/../technotes/guides/rmi/index.html">
Java<sup><font size="-1">TM</font></sup> Remote Method
Invocation (RMI)</a>
@see <a href="{@docRoot}/../technotes/guides/jndi/index.html">
Java Naming and Directory Interface<sup><font
size="-1">TM</font></sup> (JNDI)</a>
@see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045,
section 6.8, "Base64 Content-Transfer-Encoding"</a>
@since 1.5
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