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Provides the management interface for monitoring and management of the 
Java virtual machine as well as the operating system on which the 
Java virtual machine is running.  It allows both local and remote 
monitoring and management of the running Java virtual machine.  

<h4>Platform MXBeans</h4>

This package defines the management interface of the following
components:

<blockquote>
<table cellspacing=1 summary="Description of the MBeans">
<tr>
<th><p align="left">Management Interface</p></th>
<th><p align="left">Description</p></th>
</tr>
<tr>
<td> <tt>{@link java.lang.management.ClassLoadingMXBean}</tt> </td>
<td> Class loading system of the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.CompilationMXBean}</tt> </td>
<td> Compilation system of the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.MemoryMXBean}</tt> </td>
<td> Memory system of the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.ThreadMXBean}</tt> </td>
<td> Threads system of the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.RuntimeMXBean}</tt> </td>
<td> Runtime system of the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.OperatingSystemMXBean}</tt> </td>
<td> Operating system on which the Java virtual machine is running.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.GarbageCollectorMXBean}</tt> </td>
<td> Garbage collector in the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.MemoryManagerMXBean}</tt> </td>
<td> Memory manager in the Java virtual machine.</td>
</tr>
<tr>
<td> <tt>{@link java.lang.management.MemoryPoolMXBean}</tt> </td>
<td> Memory pool in the Java virtual machine.</td>
</tr>
</table>
</blockquote>

<p>
A platform MXBean is a <i>managed bean</i> that defines the management
interface for one component for the platform and is specified in the
<a href="ManagementFactory.html#MXBean">
ManagementFactory</a> class.

<p>An application can monitor the instrumentation of the 
Java virtual machine and manage certain characteristics in
the following ways:
<ul>
<li><i>Direct access to an MXBean interface</i>
    <ol type="a">
    <li>Get the MXBean instance through the static factory method
        and access the MXBean interface locally of the running
        virtual machine.</li>
    <li>Construct an MXBean proxy instance that
        forwards the method calls to a given 
        {@link javax.management.MBeanServer MBeanServer}
        by calling
        {@link java.lang.management.ManagementFactory#newPlatformMXBeanProxy
         ManagementFactory.newPlatformMXBeanProxy}.
         A proxy is typically constructed to remotely access
         an MXBean of another running virtual machine.</li>
    </ol></li>
<li><i>Indirect access via {@link javax.management.MBeanServer MBeanServer} 
       interface</i>
    <ol type="a">
    <li>Go through the 
        {@link java.lang.management.ManagementFactory#getPlatformMBeanServer
        platform MBeanServer} to access MXBeans locally or
        a specific <tt>MBeanServerConnection</tt> to access
        MXBeans remotely.
        The attributes and operations of an MXBean use only
        <em>JMX open types</em> which include basic data types, 
        {@link javax.management.openmbean.CompositeData CompositeData},
        and {@link javax.management.openmbean.TabularData TabularData} 
        defined in {@link javax.management.openmbean.OpenType OpenType}.
       </li>
    </ol></li>
</ul>

Below shows a few <a href="#examples">examples</a> of different
ways to access MXBeans.

<h4>ManagementFactory</h4>

The {@link java.lang.management.ManagementFactory} class is the management
factory class for the Java platform.  This class provides a set of 
static factory methods to obtain the MXBeans for the Java platform
to allow an application to access the MXBeans directly.

<p>A <em>platform MBeanServer</em> can be accessed with the
{@link java.lang.management.ManagementFactory#getPlatformMBeanServer
 getPlatformMBeanServer} method.  On the first call to this method,
it creates the platform MBeanServer and registers all platform MXBeans 
including platform MXBeans defined in other packages such as
{@link java.util.logging.LoggingMXBean}.  
Each platform MXBean is registered with a unique name defined in the
{@link java.lang.management.ManagementFactory ManagementFactory} class
for constructing {@link javax.management.ObjectName ObjectName}. 
This is a single MBeanServer that can be shared by different managed 
components running within the same Java virtual machine.
 
<h4>Interoperability</h4>

A management application and a platform MBeanServer of a running
virtual machine can interoperate 
without requiring classes used by the platform MXBean interfaces.
The data types being transmitted between the JMX connector
server and the connector client are JMX
{@link javax.management.openmbean.OpenType open types} and
this allows interoperation across versions.

<p>A data type used by the MXBean interfaces are mapped to
an open type when being accessed via MBeanServer interface.
The data type mapping is specified in the
{@link java.lang.management.ManagementFactory ManagementFactory} class.

<h4><a name="examples">Ways to Access MXBeans</a></h4>

There are three different ways to access the management interfaces. 

<p>
<ol>
<li>Call the methods in the MXBean directly within the same 
    Java virtual machine.
<blockquote><pre>
   RuntimeMXBean mxbean = ManagementFactory.getRuntimeMXBean();

   // Get the standard attribute "VmVendor"
   String vendor = mxbean.getVmVendor();

</pre>
</blockquote>
</li>

<li>Go through a <tt>MBeanServerConnection</tt> connecting 
    to the <tt>platform MBeanServer</tt> of a running virtual machine.</li>
<blockquote><pre>
   MBeanServerConnection mbs;

   // Connect to a running JVM (or itself) and get MBeanServerConnection
   // that has the JVM MXBeans registered in it
   ...

   try {
       // Assuming the RuntimeMXBean has been registered in mbs
       ObjectName oname = new ObjectName(ManagementFactory.RUNTIME_MXBEAN_NAME);
    
       // Get standard attribute "VmVendor"
       String vendor = (String) mbs.getAttribute(oname, "VmVendor");
   } catch (....) {
       // Catch the exceptions thrown by ObjectName constructor
       // and MBeanServer.getAttribute method
       ...
   }

</pre></blockquote>

<li>Use MXBean proxy.</li>
<blockquote><pre>
   MBeanServerConnection mbs;

   // Connect to a running JVM (or itself) and get MBeanServerConnection
   // that has the JVM MBeans registered in it
   ...

   // Get a MBean proxy for RuntimeMXBean interface
   RuntimeMXBean proxy = 
       ManagementFactory.newPlatformMXBeanProxy(mbs,
                                                ManagementFactory.RUNTIME_MXBEAN_NAME,
                                                RuntimeMXBean.class);
   // Get standard attribute "VmVendor" 
   String vendor = proxy.getVmVendor();
</pre></blockquote>
</ol>


<h4><a name="extension">Platform Extension</a></h4>

A Java virtual machine implementation may add its platform extension to
the management interface by defining platform-dependent
interfaces that extend the standard management interfaces to include
platform-specific metrics and management operations.  
The static factory methods in the <tt>ManagementFactory</tt> class will
return the MBeans with the platform extension.

<p>
It is recommended to name the platform-specific attributes with
a vendor-specific prefix such as the vendor's name to
avoid collisions of the attribute name between the future extension
to the standard management interface and the platform extension.
If the future extension to the standard management interface defines
a new attribute for a management interface and the attribute name
is happened to be same as some vendor-specific attribute's name,
the applications accessing that vendor-specific attribute would have
to be modified to cope with versioning and compatibility issues.

<p>Below is an example showing how to access a platform-specific
attribute from Sun's implementation of the <tt>RuntimeMXBean</tt>.

<p>
1) Direct access to the Sun-specific MXBean interface
<blockquote><pre>
   com.sun.management.RuntimeMXBean mxbean = 
       (com.sun.management.RuntimeMXBean) ManagementFactory.getRuntimeMXBean();

   // Get the standard attribute "VmVendor"
   String vendor = mxbean.getVmVendor();

   // Get the platform-specific attribute "Bar"
   BarType bar = mxbean.getBar();

</pre>
</blockquote>

<p>
2) Access the Sun-specific MXBean interface via <tt>MBeanServer</tt>

<blockquote><pre>
   MBeanServerConnection mbs;

   // Connect to a running JVM (or itself) and get MBeanServerConnection
   // that has the JVM MXBeans registered in it
   ...

   try {
       // Assuming the RuntimeMXBean has been registered in mbs
       ObjectName oname = new ObjectName(ManagementFactory.RUNTIME_MXBEAN_NAME);
    
       // Get standard attribute "VmVendor"
       String vendor = (String) mbs.getAttribute(oname, "VmVendor");

       // Check if this MXBean contains Sun's extension
       if (mbs.isInstanceOf(oname, "com.sun.management.RuntimeMXBean")) {
           // Get platform-specific attribute "Bar"
           BarType bar = (String) mbs.getAttribute(oname, "Bar");
       }
   } catch (....) {
       // Catch the exceptions thrown by ObjectName constructor
       // and MBeanServer methods
       ...
   }

</pre></blockquote>

<p> Unless otherwise noted, passing a <tt>null</tt> argument to a constructor
or method in any class or interface in this package will cause a {@link
java.lang.NullPointerException NullPointerException} to be thrown.

<p> The java.lang.management API is thread-safe.

@see <a href="../../../javax/management/package-summary.html">
     JMX Specification.</a>

@author  Mandy Chung
@since   1.5

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