<html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>MBeans</title><link href="styles.css" type="text/css" rel="stylesheet"><meta content="DocBook XSL Stylesheets V1.78.1" name="generator"><link rel="home" href="index.html" title="MX4J English Documentation"><link rel="up" href="ch07.html" title="Chapter 7. MX4J Examples"><link rel="prev" href="ch07.html" title="Chapter 7. MX4J Examples"><link rel="next" href="ch07s03.html" title="Tools"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">MBeans</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="ch07.html">Prev</a> </td><th align="center" width="60%">Chapter 7. MX4J Examples</th><td align="right" width="20%"> <a accesskey="n" href="ch07s03.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="N10EE7"></a>MBeans</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="N10EEA"></a>RMI MBean example</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="N10EED"></a>Introduction</h4></div></div></div><p>
The purpose of this example is to give some guideline on how to expose RMI remote objects also as MBeans.
</p><p>
This will give to server administrators the possibility to manage RMI remote objects in the JMX sense. This
means that may be possible to start, stop and restart the service implemented by the remote object; and also
checking if it is running, or ask to reload configurations files.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="N10EF4"></a>The example classes</h4></div></div></div><p>
The example java source files can be found in the examples directory under mbeans/rmi, they include:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><code class="classname">Server</code> (the class that starts the remote service)
</li><li class="listitem"><code class="classname">Client</code> (the client class)
</li><li class="listitem"><code class="classname">MyRemoteService</code> (the remote interface)
</li><li class="listitem"><code class="classname">MyRemoteServiceObjectMBean</code> (the management interface)
</li><li class="listitem"><code class="classname">MyRemoteServiceObject</code> (the MBean that implements the remote interface)
</li></ul></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="N10F0F"></a>Understanding the example</h4></div></div></div><p>
The remote object is, at the same time an MBean and an RMI remote object.
</p><p>
Clients can see it through 2 interfaces: users of the service see it through the
<span class="emphasis"><em>remote interface</em></span>
(
<code class="classname">MyRemoteService</code>), while management application (such as the HTTP adaptor)
see it through the
<span class="emphasis"><em>management interface</em></span> (
<code class="classname">MyRemoteServiceObjectMBean</code>).
<br>
The remote interface contains only one method:
</p><p>
<span style="color: red"><funcdef>public void
<code class="function">sayHello(String name)</code>
</funcdef></span>
</p><p>
that will execute client's requests.
<br>
The management interface, conversely, contains 3 methods:
</p><p>
<span style="color: red"><funcdef>public void
<code class="function">start()</code>
</funcdef></span>
<br>
<span style="color: red"><funcdef>public void
<code class="function">stop()</code>
</funcdef></span>
<br>
<span style="color: red"><funcdef>public boolean
<code class="function">isRunning()</code>
</funcdef></span>
</p><p>
that will be used by management application such as the HTTP adaptor.
</p><p>
Notice that users of the remote interface cannot invoke methods of the management interface, as well as management
application cannot invoke methods of the remote interface.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="N10F50"></a>The implementation</h4></div></div></div><p>
The purpose of the
<code class="classname">Server</code> class is only to start a JMX Agent by instantiating the MBeanServer,
register the service we want to expose, and starting it.
</p><p>
</p><div class="example"><a name="N10F5A"></a><p class="title"><b>Example 7.4. The
<code class="classname">Server</code> class
</b></p><div class="example-contents"><pre class="programlisting">
public class Server
{
public static void main(String[] args) throws Exception
{
MBeanServer server = MBeanServerFactory.createMBeanServer();
ObjectName name = new ObjectName("examples:type=remote");
MyRemoteServiceObject remote = new MyRemoteServiceObject();
server.registerMBean(remote, name);
MyRemoteServiceObjectMBean managed = (MyRemoteServiceObjectMBean)MBeanServerInvocationHandler.newProxyInstance(server, name, MyRemoteServiceObjectMBean.class, false);
managed.start();
}
}
</pre></div></div><p><br class="example-break">
</p><p>
The remote object, instance of
<code class="classname">MyRemoteServiceObject</code> class, is worth some more detail.
<br>
First notice that it extends
<code class="classname">java.rmi.server.RemoteServer</code> and not
<code class="classname">java.rmi.server.UnicastRemoteObject</code>. This is done to avoid that the object is automatically
exported to the RMI runtime when creating it, since we want to control the export and unexport via the
<code class="function">start()</code> and
<code class="function">stop()</code> methods of the management interface.
<br>
Second, notice the symmetry of the
<code class="function">start()</code> and
<code class="function">stop()</code> methods:
<code class="function">start()</code> export the object to the RMI runtime and binds it in the naming, while
<code class="function">stop()</code>
unbinds it from the naming and unexport it from the RMI runtime.
</p><p>
</p><div class="example"><a name="N10F8D"></a><p class="title"><b>Example 7.5. The
<code class="classname">MyRemoteServiceObject</code> class
</b></p><div class="example-contents"><pre class="programlisting">
public class MyRemoteServiceObject extends RemoteServer implements MyRemoteService, MyRemoteServiceObjectMBean
{
private boolean m_running;
public MyRemoteServiceObject() throws RemoteException {}
public void sayHello(String name) throws RemoteException
{
System.out.println("Hello, " + name);
}
public void start() throws Exception
{
if (!m_running)
{
UnicastRemoteObject.exportObject(this);
InitialContext ctx = new InitialContext();
ctx.rebind(JNDI_NAME, this);
m_running = true;
System.out.println("My remote service started successfully");
}
}
public void stop() throws Exception
{
if (m_running)
{
InitialContext ctx = new InitialContext();
ctx.unbind(JNDI_NAME);
UnicastRemoteObject.unexportObject(this, false);
m_running = false;
System.out.println("My remote service stopped successfully");
}
}
public boolean isRunning()
{
return m_running;
}
}
</pre></div></div><p><br class="example-break">
</p><p>
Thus, will be possible to start the service via a management application and let it available to users;
and will be possible to stop it, maybe changing some configuration file (not in this simple example, but you
got the picture), and restarting it,
<span class="emphasis"><em>WITHOUT</em></span> shutting down other services that may have
been started by the same JMX Agent.
</p><p>
The implementation of the
<code class="function">sayHello(String name)</code> method is straightforward, as well as
the
<code class="function">isRunning()</code> one that, accessible from management applications, returns if the
service is running or not.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="N10FA6"></a>Compiling the example files</h4></div></div></div><p>
The above classes must be compiled using
<span class="emphasis"><em>javac</em></span>, and the
<code class="classname">MyRemoteServiceObject</code> class
must be compiled using
<span class="emphasis"><em>rmic</em></span>.
</p><p>
Let's suppose you unpack the MX4J distribution in the mx4j-
<span class="emphasis"><em>ver</em></span> directory; from this directory you issue these
commands:
</p><p>
C:\mx4j-
<span class="emphasis"><em>ver</em></span>>javac -classpath lib\mx4j-jmx.jar examples\mbeans\rmi\*.java
<br>
C:\mx4j-
<span class="emphasis"><em>ver</em></span>>rmic mx4j.examples.mbeans.rmi.MyRemoteServiceObject
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="N10FC3"></a>Running the example</h4></div></div></div><p>
To run the example, three consoles are needed:
</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">One for the
<span class="emphasis"><em>rmiregistry</em></span></li><li class="listitem">One for the server</li><li class="listitem">One for the client</li></ul></div><p>
</p><p>
For the rmiregistry, you need to have in the classpath the RMI stub of the
<code class="classname">MyRemoteServiceObject</code>
class you just compiled with
<span class="emphasis"><em>rmic</em></span>. Then you can start it by typing the following command:
</p><p>
C:\mx4j-
<span class="emphasis"><em>ver</em></span>>set classpath=.
<br>
C:\mx4j-
<span class="emphasis"><em>ver</em></span>>rmiregistry
</p><p>
For the server, you need all the compiled classes (apart for the
<code class="classname">Client</code> class),
mx4j-jmx.jar (the JMX implementation), and a suitable
<span class="emphasis"><em>jndi.properties</em></span> file (there is a default
one shipped with this example) in the classpath. Then you can start the server with the following command:
</p><p>
C:\mx4j-
<span class="emphasis"><em>ver</em></span>>java -cp .;examples;lib\mx4j-jmx.jar mx4j.examples.mbeans.rmi.Server
</p><p>
For the client, you need the
<code class="classname">Client</code> class, the remote interface and the RMI stub, and a suitable
<span class="emphasis"><em>jndi.properties</em></span> file (there is a default one shipped with this example).
Then you can start the client with the following command:
</p><p>
C:\mx4j-
<span class="emphasis"><em>ver</em></span>>java -cp .;examples mx4j.examples.mbeans.rmi.Client
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