Exposing Collection<Something> from ManagedResource bean?

Question

@ManagedResource
@Component
public class MyBean {
   Map<String, Something> map = new HashMap<String, Something>();

   @ManagedAttribute
   public Collection<Something> getFoo() {
       return map.values();
   }
}

The foo attributed shows as 'unavailable' in the visualvm mbeans tab. Why?

Answer 1

I annotated the bean with @MXBean then returned CompositeData[] creating instances of CompositeDataSupport.

Answer 2

The MXBean solution is the way to go most of the time, although there is a slightly easier way than generating CompositeDataSupport instances. Let's say your class is:

public class Something {
  private String foo;
  private Date date;
  <Insert Ctor here>
  public String getFoo() {
    return foo;
  }
  public Date getDate() {
    return date;
  }
}

You can create an MBean interface as follows:

public interface SomethingMBean {  // same package please...
  public String getFoo();
  public Date getDate();
}

Make Something implement SomethingMBean:

public class Something implements SomethingMBean {
   .....
}

Now in your actual MBean (the @MXBean annotated one), you can define a method like this:

   public List<SomethingMBean> getSomethings() {
      .....
   }

The Java6+ MBeanServer will automatically generate CompositeDataTypes and instances at runtime. As a simple diagnostic tool, I frequently swap out the JVM's ThreadMXBean with a wrapped one that exposes ThreadInfos using this technique. (See ExtendedThreadManager for an example) It looks like this in JConsole:

Answer 3

It will work if Something is part of the JDK (such as String).

If Something is a custom class, VisualVM won't know about it; hence 'unavailable'.

You can see more information if you go to the operations tab and click getFoo().

I have not tried it, but I believe you can add stuff to VisualVM's class path with

jvisualvm -cp:a /path/to/Something/top/level/package

(or jar).

Then, it might work; even then, though, Something (and its fields) needs to be Serializable.