330 lines
13 KiB
HTML
330 lines
13 KiB
HTML
<html>
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<head>
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<title>RMI connector</title>
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</head>
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<body bgcolor="white">
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<p>The RMI connector is a connector for the JMX Remote API that
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uses RMI to transmit client requests to a remote MBean server.
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This package defines the classes that the user of an RMI
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connector needs to reference directly, for both the client and
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server sides. It also defines certain classes that the user
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will not usually reference directly, but that must be defined so
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that different implementations of the RMI connector can
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interoperate.</p>
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<p>The RMI connector supports the JRMP transport for RMI.</p>
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<p>Like most connectors in the JMX Remote API, an RMI connector
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usually has an address, which
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is a {@link javax.management.remote.JMXServiceURL
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JMXServiceURL}. The protocol part of this address is
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<code>rmi</code> for a connector that uses the default RMI
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transport (JRMP).</p>
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<p>There are two forms for RMI connector addresses:</p>
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<ul>
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<li>
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In the <em>JNDI form</em>, the URL indicates <em>where to find
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an RMI stub for the connector</em>. This RMI stub is a Java
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object of type {@link javax.management.remote.rmi.RMIServer
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RMIServer} that gives remote access to the connector server.
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With this address form, the RMI stub is obtained from an
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external directory entry included in the URL. An external
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directory is any directory recognized by {@link javax.naming
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JNDI}, typically the RMI registry, LDAP, or COS Naming.
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<li>
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In the <em>encoded form</em>, the URL directly includes the
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information needed to connect to the connector server. When
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using RMI/JRMP, the encoded form is the serialized RMI stub
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for the server object, encoded using BASE64 without embedded
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newlines.
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</ul>
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<p>Addresses are covered in more detail below.</p>
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<h2>Creating an RMI connector server</h2>
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<p>The usual way to create an RMI connector server is to supply an
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RMI connector address to the method {@link
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javax.management.remote.JMXConnectorServerFactory#newJMXConnectorServer
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JMXConnectorServerFactory.newJMXConnectorServer}. The MBean
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server to which the connector server is attached can be
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specified as a parameter to that method. Alternatively, the
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connector server can be registered as an MBean in that MBean
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server.</p>
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<p>An RMI connector server can also be created by constructing an
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instance of {@link
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javax.management.remote.rmi.RMIConnectorServer
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RMIConnectorServer}, explicitly or through the MBean server's
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<code>createMBean</code> method.</p>
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<h3>Choosing the RMI transport</h3>
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<p>You can choose the RMI transport by specifying
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<code>rmi</code> in the <code><em>protocol</em></code> part of the
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<code>serviceURL</code> when creating the connector server. You
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can also create specialized connector servers by instantiating
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an appropriate subclass of {@link
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javax.management.remote.rmi.RMIServerImpl RMIServerImpl} and
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supplying it to the <code>RMIConnectorServer</code>
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constructor.</p>
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<h3><a id="servergen">Connector addresses generated by the
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server</a></h3>
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<p>If the <code>serviceURL</code> you specify has an empty URL
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path (after the optional host and port), or if you do not
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specify a <code>serviceURL</code>, then the connector server
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will fabricate a new <code>JMXServiceURL</code> that clients can
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use to connect:</p>
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<ul>
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<li><p>If the <code>serviceURL</code> looks like:</p>
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<pre>
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<code>service:jmx:rmi://<em>host</em>:<em>port</em></code>
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</pre>
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<p>then the connector server will generate an {@link
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javax.management.remote.rmi.RMIJRMPServerImpl
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RMIJRMPServerImpl} and the returned <code>JMXServiceURL</code>
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looks like:</p>
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<pre>
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<code>service:jmx:rmi://<em>host</em>:<em>port</em>/stub/<em>XXXX</em></code>
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</pre>
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<p>where <code><em>XXXX</em></code> is the serialized form of the
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stub for the generated object, encoded in BASE64 without
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newlines.</p>
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<li><p>If there is no <code>serviceURL</code>, there must be a
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user-provided <code>RMIServerImpl</code>. The connector server
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will generate a <code>JMXServiceURL</code> using the <code>rmi</code>
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form.</p>
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</ul>
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<p>The <code><em>host</em></code> in a user-provided
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<code>serviceURL</code> is optional. If present, it is copied
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into the generated <code>JMXServiceURL</code> but otherwise
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ignored. If absent, the generated <code>JXMServiceURL</code>
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will have the local host name.</p>
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<p>The <code><em>port</em></code> in a user-provided
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<code>serviceURL</code> is also optional. If present, it is
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also copied into the generated <code>JMXServiceURL</code>;
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otherwise, the generated <code>JMXServiceURL</code> has no port.
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For an <code>serviceURL</code> using the <code>rmi</code>
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protocol, the <code><em>port</em></code>, if present, indicates
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what port the generated remote object should be exported on. It
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has no other effect.</p>
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<p>If the user provides an <code>RMIServerImpl</code> rather than a
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<code>JMXServiceURL</code>, then the generated
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<code>JMXServiceURL</code> will have the local host name in its
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<code><em>host</em></code> part and no
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<code><em>port</em></code>.</p>
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<h3><a id="directory">Connector addresses based on directory
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entries</a></h3>
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<p>As an alternative to the generated addresses just described,
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the <code>serviceURL</code> address supplied when creating a
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connector server can specify a <em>directory address</em> in
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which to store the provided or generated <code>RMIServer</code>
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stub. This directory address is then used by both client and
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server.</p>
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<p>In this case, the <code>serviceURL</code> has the following form:</p>
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<pre>
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<code>service:jmx:rmi://<em>host</em>:<em>port</em>/jndi/<em>jndi-name</em></code>
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</pre>
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<p>Here, <code><em>jndi-name</em></code> is a string that can be
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supplied to {@link javax.naming.InitialContext#bind
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javax.naming.InitialContext.bind}.</p>
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<p>As usual, the <code><em>host</em></code> and
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<code>:<em>port</em></code> can be omitted.</p>
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<p>The connector server will generate an
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<code>RMIServerImpl</code> based on the protocol
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(<code>rmi</code>) and the <code><em>port</em></code> if any. When
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the connector server is started, it will derive a stub from this
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object using its {@link
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javax.management.remote.rmi.RMIServerImpl#toStub toStub} method
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and store the object using the given
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<code><em>jndi-name</em></code>. The properties defined by the
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JNDI API are consulted as usual.</p>
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<p>For example, if the <code>JMXServiceURL</code> is:
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<pre>
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<code>service:jmx:rmi://ignoredhost/jndi/rmi://myhost/myname</code>
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</pre>
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then the connector server will generate an
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<code>RMIJRMPServerImpl</code> and store its stub using the JNDI
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name
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<pre>
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<code>rmi://myhost/myname</code>
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</pre>
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which means entry <code>myname</code> in the RMI registry
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running on the default port of host <code>myhost</code>. Note
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that the RMI registry only allows registration from the local
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host. So, in this case, <code>myhost</code> must be the name
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(or a name) of the host that the connector server is running
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on.
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<p>In this <code>JMXServiceURL</code>, the first <code>rmi:</code>
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specifies the RMI
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connector, while the second <code>rmi:</code> specifies the RMI
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registry.
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<p>As another example, if the <code>JMXServiceURL</code> is:
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<pre>
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<code>service:jmx:rmi://ignoredhost/jndi/ldap://dirhost:9999/cn=this,ou=that</code>
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</pre>
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then the connector server will generate an
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<code>RMIJRMPServerImpl</code> and store its stub using the JNDI
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name
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<pre>
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<code>ldap://dirhost:9999/cn=this,ou=that</code>
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</pre>
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which means entry <code>cn=this,ou=that</code> in the LDAP
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directory running on port 9999 of host <code>dirhost</code>.
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<p>If the <code>JMXServiceURL</code> is:
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<pre>
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<code>service:jmx:rmi://ignoredhost/jndi/cn=this,ou=that</code>
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</pre>
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then the connector server will generate an
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<code>RMIJRMPServerImpl</code> and store its stub using the JNDI
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name
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<pre>
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<code>cn=this,ou=that</code>
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</pre>
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For this case to work, the JNDI API must have been configured
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appropriately to supply the information about what directory to
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use.
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<p>In these examples, the host name <code>ignoredhost</code> is
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not used by the connector server or its clients. It can be
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omitted, for example:</p>
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<pre>
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<code>service:jmx:rmi:///jndi/cn=this,ou=that</code>
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</pre>
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<p>However, it is good practice to use the name of the host
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where the connector server is running. This is often different
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from the name of the directory host.</p>
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<h3>Connector server attributes</h3>
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<p>When using the default JRMP transport, RMI socket factories can
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be specified using the attributes
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<code>jmx.remote.rmi.client.socket.factory</code> and
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<code>jmx.remote.rmi.server.socket.factory</code> in the
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<code>environment</code> given to the
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<code>RMIConnectorServer</code> constructor. The values of these
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attributes must be of type {@link
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java.rmi.server.RMIClientSocketFactory} and {@link
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java.rmi.server.RMIServerSocketFactory}, respectively. These
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factories are used when creating the RMI objects associated with
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the connector.</p>
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<h2>Creating an RMI connector client</h2>
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<p>An RMI connector client is usually constructed using {@link
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javax.management.remote.JMXConnectorFactory}, with a
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<code>JMXServiceURL</code> that has <code>rmi</code> as its protocol.</p>
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<p>If the <code>JMXServiceURL</code> was generated by the server,
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as described above under <a href="#servergen">"connector
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addresses generated by the server"</a>, then the client will
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need to obtain it directly or indirectly from the server.
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Typically, the server makes the <code>JMXServiceURL</code>
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available by storing it in a file or a lookup service.</p>
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<p>If the <code>JMXServiceURL</code> uses the directory syntax, as
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described above under <a href="#directory">"connector addresses
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based on directory entries"</a>, then the client may obtain it
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as just explained, or client and server may both know the
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appropriate directory entry to use. For example, if the
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connector server for the Whatsit agent uses the entry
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<code>whatsit-agent-connector</code> in the RMI registry on host
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<code>myhost</code>, then client and server can both know
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that the appropriate <code>JMXServiceURL</code> is:</p>
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<pre>
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<code>service:jmx:rmi:///jndi/rmi://myhost/whatsit-agent-connector</code>
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</pre>
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<p>If you have an RMI stub of type {@link
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javax.management.remote.rmi.RMIServer RMIServer}, you can
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construct an RMI connection directly by using the appropriate
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constructor of {@link javax.management.remote.rmi.RMIConnector
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RMIConnector}.</p>
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<h2>Dynamic code downloading</h2>
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<p>If an RMI connector client or server receives from its peer an
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instance of a class that it does not know, and if dynamic code
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downloading is active for the RMI connection, then the class can
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be downloaded from a codebase specified by the peer.
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{@extLink rmi_guide Java RMI Guide} explains this in more detail.</p>
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@see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045,
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section 6.8, "Base64 Content-Transfer-Encoding"</a>
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@since 1.5
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</body>
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</html>
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