I have reached my conclusion: I don't know what I am doing. :-(
I now realize that the query expression will filter MBeans based on the values
of the properties defined for the MBean. I mistakenly thought that parts of
the MBean name were the attributes that I could query on. That is, an MBean
with name "foo.bar:name1=xxx,name2=yyy" had attributes name1 and name2 and thus
I could query on those. But actually, if this MBean has properties prop1 and
prop2, I can use a query to find an MBean with particular values for properties
prop1 or prop2. The tutorials that were confusing to me at first are now a lot
clearer.
But, I still have room to complain. :-)
First, class org.jboss.mx.server.MBeanServerImpl, method queryMBean has this
code:
try
| {
| return queryExp.apply(objectName);
| }
| catch (Exception e)
| {
| return false;
| }
Not quite sure who thought it was a good idea to throw away the exception. So,
I added a logging statement to the code to find out what exception was being
thrown and noticed this exception:
|
| Exception in thread "main" java.lang.NullPointerException
| at
javax.management.BadAttributeValueExpException.toString(BadAttributeValueExpException.java:71)
| at
org.apache.log4j.spi.VectorWriter.println(ThrowableInformation.java:88)
| . . .
OK, so printing of the stack trace blew up. Seems to be "a bad thing" to me.
Looking at the above toString method, I see:
return "Bad attribute value expression: " + val.toString();
Hmm, not only is the call to toString on variable val superfluous, but it is
also a bad idea because if val is nul? (you get the idea). OK, so get rid of
the toString call on val so that I can finally get my exception printed out.
And I then found another instance where an exception was being thrown away in
javax.management.AttributeValueExp.getAttribute:
try
| {
| MBeanServer mbs = QueryEval.getMBeanServer();
| return QueryEval.getMBeanServer().getAttribute(name, attr);
| }
| catch (Exception e)
| {
| return null;
| }
The toString bug should be fixed. Should I write a JIRA?
For the dropped exceptions, I thought it would be nice to at least log them.
But, given the way the code is written, every query will generate a lot of
exceptions because if you query for a particular property, an exception is
thrown for every MBEan that doesn't have such a property. But this could be
handled by catching something other than Exception. Not sure if this is worth
opening a JIRA or not.
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