18.2.2.1 JmxMBeanServerImpl
As stated previously, JmxMBeanServerImpl extends the JmxMBeanServer empty skeleton class. JmxMBeanServerImpl also instantiates a subclass of TableJmxMBeanTable, to mirror the MBeans registered in an MBean server.
Example 18–4 Subclassing TableJmxMBeanTable
[...]
private final void inittables() {
JmxMBeanTable = new TableJmxMBeanTable(myMib,null) {
public Object createJmxMBeanEntryMBean(SnmpMibSubRequest req,
SnmpOid rowOid,
int depth,
ObjectName entryObjName,
SnmpMibTable meta,
Integer aJmxMBeanIndex)
throws SnmpStatusException {
return JmxMBeanServerImpl.this.
createJmxMBeanEntryMBean(req,rowOid,depth,entryObjName,
meta,aJmxMBeanIndex);
}
public void removeEntryCb(int pos, SnmpOid row,
ObjectName name,
Object entry, SnmpMibTable meta)
throws SnmpStatusException {
super.removeEntryCb(pos,row,name,entry,meta);
final JmxMBeanEntryMBean e =
(JmxMBeanEntryMBean) entry;
final EnumJmxMBeanRowStatus destroy =
new EnumJmxMBeanRowStatus(EnumRowStatus.destroy);
e.setJmxMBeanRowStatus(destroy);
}
};
JmxMBeanTable.setCreationEnabled(true);
}
[...]
In Example 18–4, JmxMBeanServerImpl defines a method, inittables, to instantiate and initialize its table objects. The inittables method creates a new instance of TableJmxMBeanTable, and overrides it so that its createJmxMBeanEntryMBean method returns a JmxMBeanEntryImpl object instead of the default JmxMBeanEntry object. This is done by defining a new createJmxMBeanEntryMBean method in the customized JmxMBeanEntryImpl class (see Example 18–5), and calling it on the parent JmxMBeanServerImpl object from the overridden TableJmxMBeanTable object, as shown in Example 18–4.
The removeEntryCb method is overridden, so that table entries representing MBeans also delete their associated entries in the jmxMBeanAtrrTable by calling setJmxMBeanRowStatus(destroy) when they are removed from the jmxMBeanTable.
Example 18–5 createJmxMBeanEntryMBean Method
[...]
private Object createJmxMBeanEntryMBean(SnmpMibSubRequest req,
SnmpOid rowOid,
int depth,
ObjectName entryObjName,
SnmpMibTable meta,
Integer aJmxMBeanIndex)
throws SnmpStatusException {
SnmpVarBind rowStatusVb = req.getRowStatusVarBind();
if (rowStatusVb == null)
throw new SnmpStatusException(
SnmpStatusException.snmpRspNoCreation);
if (! isAvailable(aJmxMBeanIndex.intValue())) {
if (Boolean.getBoolean("info"))
System.out.println("Index is not suitable: "
+ aJmxMBeanIndex);
throw new SnmpStatusException(
SnmpStatusException.snmpRspInconsistentValue);
}
JmxMBeanEntryImpl entry =
new JmxMBeanEntryImpl(myMib,this);
entry.JmxMBeanIndex = aJmxMBeanIndex;
entry.createFromRemote(req,rowStatusVb);
return entry;
}
[...]
As shown in Example 18–4, the createJmxMBeanEntryMBean method is called when a remote SNMP Manager creates a new row in a jmxMBeanTable. Example 18–5 shows how the createJmxMBeanEntryMBean method is overridden by the JmxMBeanServerImpl class, to add new entries in the jmxMBeanAttrTable as the rows are created in the table.
Of the parameters the customized version of createJmxMBeanEntryMBean takes when it is started, the following are the most significant..
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req, the SnmpMibSubRequest containing the VarBind list pertaining to this new row.
-
rowOid, the index of this new row's OID.
-
meta, the SnmpMibTable metadata object of the jmxMBeanTable.
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aJmxMBeanIndex, the value of the new entry's JmxMBeanIndex index variable.
The createJmxMBeanEntryMBean method checks first of all whether the VarBind list found when req calls getRowStatusVarBind() is valid. It then checks whether the row's OID index is available. Once it has established that both the VarBind and the index are viable, it proceeds to create a JmxMBeanEntryImpl instance, entry. Calling createFromRemote() at this point ensures that createMBean() will be called when the new entry is eventually activated.
As mentioned previously, JmxMBeanServerImpl is also configured to listen for notifications of the type MBeanServerNotifications coming from the MBean server.
Example 18–6 Listening for Notifications
[...]
public synchronized void start() {
started = true;
try {
final ObjectName delegate =
new ObjectName("JMImplementation:type=MBeanServerDelegate");
myMib.getMibServer().
addNotificationListener(delegate,mbsListener,null,null);
try {
Set mbeans = myMib.getMibServer().queryNames(null,null);
for (final Iterator it = mbeans.iterator();
it.hasNext();) {
final ObjectName name = (ObjectName) it.next();
if (mustShow(name)) showMBean("start",name);
}
} catch (Exception x) {
try {
myMib.getMibServer().
removeNotificationListener(delegate,mbsListener);
} catch (Exception e) { /* OK */ }
throw x;
}
} catch (Exception x) {
started = false;
System.err.println("Failed to start MBean Table: " + x);
if (Boolean.getBoolean("debug")) x.printStackTrace();
}
}
[...]
The start() method shown in Example 18–5 starts a notification listener in the MIB server that listens out for notifications from the MBeanServerDelegate. It also populates the jmxMBeanTable and jmxMBeanAttrTable with the initial content of the MBean server. These tables are then updated as and when notifications are received, as shown in Example 18–7.
Example 18–7 Handling Notifications
[...]
private void handleMBSNotification(Notification notif, Object handback) {
synchronized(this) { if (!started) return; }
if (notif instanceof MBeanServerNotification) {
final MBeanServerNotification n =
(MBeanServerNotification) notif;
final String nt = n.getType();
final ObjectName mbeanName = n.getMBeanName();
if (MBeanServerNotification.REGISTRATION_NOTIFICATION.
equals(nt)) {
synchronized (this) {
if (mustShow(mbeanName)) {
showMBean(nt,mbeanName);
}
}
} else if (MBeanServerNotification.UNREGISTRATION_NOTIFICATION.
equals(nt)) {
synchronized (this) {
if (mustHide(mbeanName)) {
hideMBean(nt,mbeanName);
}
}
}
}
}
[...]
The handleMBSNotification method that JmxMBeanServerImpl defines begins by checking that the correct type of notification has been received. If the notification is of the type MBeanServerNotification.REGISTRATION_NOTIFICATION, then a method named showMBean() is called. Otherwise, if MBeanServerNotification.UNREGISTRATION_NOTIFICATION is received, then the MBean is hidden with a call to hideMBean. The showMBean() method is shown in Example 18–8.
Example 18–8 Exposing MBeans through the SNMP Tables
[...]
private void showMBean(String operation,ObjectName name,int index) {
try {
JmxMBeanEntry entry = new JmxMBeanEntryImpl(myMib,this);
entry.JmxMBeanIndex = new Integer(index);
entry.setJmxMBeanObjectName(name.toString());
JmxMBeanTable.addEntry(entry);
names.put(name, entry);
entry.setJmxMBeanRowStatus(
new EnumJmxMBeanRowStatus(EnumRowStatus.active));
if (Boolean.getBoolean("info"))
System.out.println("ADDED: JmxMBeanTable["+index+"]="+name);
} catch (Exception x) {
System.err.println("Failed to add MBean entry: " + name);
if (Boolean.getBoolean("debug")) x.printStackTrace();
}
}
[...]
The showMBean method adds the MBeans that handleMBSNotification learns about to the SNMP table JmxMBeanTable as JmxMBeanEntryImpl row entries. The status of the row is set to active. The MBean discovered by the notification listener is thus entered in the SNMP table as a row entry.
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