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List:       openjdk-serviceability-dev
Subject:    Re: Soften interface for javax.management.ObjectName.getInstance and friends
From:       Daniel Fuchs <daniel.fuchs () oracle ! com>
Date:       2017-02-24 13:44:04
Message-ID: ccbf78c7-9bb8-788f-6d92-c7e2df09a51b () oracle ! com
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Hi Dave,

I'm not sure this is quite a good idea because
order doesn't count when comparing ObjectNames.

So the folder analogy would just be a lure:
/a/b/c would be equal to /a/c/b

That said - I can see value in trying to get rid
of the legacy Hashtable - so adding a new method
that takes a Map<String,String> wouldn't necessarily
be a bad thing :-)

A work around for your use case would be to use:

  static ObjectName getInstance(String name)

instead of

  static ObjectName getInstance(String domain
                                Hashtable<String,String> table)

An object name has both a string representation
and a canonical representation.
IIRC we did try to preserve the original string
representation, even if it's not canonical.
It's also preserved in the serial form.

See:
https://docs.oracle.com/javase/8/docs/api/javax/management/ObjectName.html#getKeyPropertyListString--

Hope this helps,

-- daniel


On 24/02/17 00:17, Dave Brosius wrote:
> Greetings. the method
>
> public static ObjectName getInstance(String domain,
> Hashtable<String,String> table)
>         throws MalformedObjectNameException {
>         return new ObjectName(domain, table);
>     }
>
> in javax.management.ObjectName allows for a provided Hashtable to
> specify properties for the objectname.
>
> The semantics of an ObjectName don't consider the order of these
> properties, however certain tools like jconsole (when used as a name for
> a jmx property) does consider the order.
>
> If you wish to create a folder structure to report metrics in jmx, you
> need to use this properties map to specify the folder names. JConsole,
> then, uses order of iteration to determine the order of the folder
> hierarchy.
>
> Suppose you want a folder hierarchy similar to a package name, you may
> specify properties like
>
> table.put("a0", "com");
> table.put("a1", "acme");
> table.put("name", "MyMetric");
>
> in hopes of producing a metric in JConsole in the folder structure,
> com/acme/MyMetric.
>
> The problem is of course, that the argument is a Hashtable, not a Map,
> and so the items are not ordered at all, yet JConsole uses iteration
> order to build the path, so you may get
>
> acme/ao/MyMetric or MyMetric/acme/ao or .....
>
> This means if you really want to have ordered packages, you have to
> derive from Hashtable, and override the entrySet() method, including
> that set's iterator() to return the values in the order you wish to have
> them shown.
>
> That is really janky.
>
> I'm proposing that the interface for getInstance be softened to
>
> public static ObjectName getInstance(String domain,
>                                          Map<String,String> table)
>
> as well as
>
> public ObjectName(String domain, Map<String, String> table)
>
> thoughts?
>

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