Platform MXBean

A platform MXBean is a managed bean that conforms to the JMX Instrumentation Specification and only uses a set of basic data types. Each platform MXBean is a {@link java.lang.management.PlatformManagedObject} with a unique {@linkplain java.lang.management.PlatformManagedObject#getObjectName name}.

ManagementFactory

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.

A platform MBeanServer 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 {@linkplain java.lang.management.PlatformManagedObject platform MXBeans}. Each platform MXBean is registered with a unique name defined in the specification of the management interface. This is a single MBeanServer that can be shared by different managed components running within the same Java virtual machine.

Interoperability

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 {@linkplain javax.management.openmbean.OpenType open types} and this allows interoperation across versions. A data type used by the MXBean interfaces are mapped to an open type when being accessed via MBeanServer interface. See the MXBean specification for details.

Ways to Access MXBeans

An application can monitor the instrumentation of the Java virtual machine and the runtime in the following ways:

1. Direct access to an MXBean interface

• Get an MXBean instance locally in the running Java virtual machine:

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

  Or by calling the {@link java.lang.management.ManagementFactory#getPlatformMXBean(Class) getPlatformMXBean} or {@link java.lang.management.ManagementFactory#getPlatformMXBeans(Class) getPlatformMXBeans} method:

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

• Construct an MXBean proxy instance that forwards the method calls to a given MBeanServer:

     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 =
         {@link java.lang.management.ManagementFactory#getPlatformMXBean(MBeanServerConnection, Class)
         ManagementFactory.getPlatformMXBean}(mbs,
                                             RuntimeMXBean.class);
     // Get standard attribute "VmVendor"
     String vendor = proxy.getVmVendor();
  

  A proxy is typically used to access an MXBean in a remote Java virtual machine. An alternative way to create an MXBean proxy is:

     RuntimeMXBean proxy =
         {@link java.lang.management.ManagementFactory#newPlatformMXBeanProxy
                ManagementFactory.newPlatformMXBeanProxy}(mbs,
                                                  ManagementFactory.RUNTIME_MXBEAN_NAME,
                                                  RuntimeMXBean.class);
  

2. Indirect access to an MXBean interface via MBeanServer

• Go through the {@link java.lang.management.ManagementFactory#getPlatformMBeanServer platform MBeanServer} to access MXBeans locally or a specific {@code MBeanServerConnection} to access MXBeans remotely. The attributes and operations of an MXBean use only JMX open types 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}.

     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
         ...
     }
  

Platform Extension

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 ManagementFactory class will return the MXBeans with the platform extension.

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.

Below is an example showing how to access an attribute from the platform extension:

1) Direct access to the Oracle-specific MXBean interface

   List<com.sun.management.GarbageCollectorMXBean> mxbeans =
       ManagementFactory.getPlatformMXBeans(com.sun.management.GarbageCollectorMXBean.class);

   for (com.sun.management.GarbageCollectorMXBean gc : mxbeans) {
       // Get the standard attribute "CollectionCount"
       String count = mxbean.getCollectionCount();

       // Get the platform-specific attribute "LastGcInfo"
       GcInfo gcinfo = gc.getLastGcInfo();
       ...
   }

2) Access the Oracle-specific MXBean interface via MBeanServer through proxy

   MBeanServerConnection mbs;

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

   List<com.sun.management.GarbageCollectorMXBean> mxbeans =
       ManagementFactory.getPlatformMXBeans(mbs, com.sun.management.GarbageCollectorMXBean.class);

   for (com.sun.management.GarbageCollectorMXBean gc : mxbeans) {
       // Get the standard attribute "CollectionCount"
       String count = mxbean.getCollectionCount();

       // Get the platform-specific attribute "LastGcInfo"
       GcInfo gcinfo = gc.getLastGcInfo();
       ...
   }

Unless otherwise noted, passing a null 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.

The java.lang.management API is thread-safe. @see JMX Specification. @author Mandy Chung @since 1.5