Attribute in MBean is different from the one received by web app

Question

I have a service that's can be accessed via jconsole/Visual VM.

@ManagedResource
public class MyService
{
  private String foo;

  @ManagedAttribute
  public void setFoo(String newVal) { this.foo = newVal; }

  @ManagedAttribute
  public String getFoo() { return this.foo; }

  //some other things here that access foo
}

But looks like the value of foo received by the web app controller doesn't always match the value I get when I click getFoo() in either jconsle or visual VM. Also, the debugger shows me that the value my controller get is not what I see in jconsole.

Any idea?

Answer 1

But looks like the value of foo received by the web app controller doesn't always match the value I get when I click getFoo() in either jconsle or visual VM. Also, the debugger shows me that the value my controller get is not what I see in jconsole.

I'm not sure but I suspect that the value foo is not being properly memory synchronized between the various threads. You should make foo be volatile if it being updated by a different thread than the one displaying the value -- or put up with JMX being out of date.

private volatile String foo;

Certainly the JMX request is being made from a different thread that your web-app would be handled by. I would have thought, however, that the debugger would not have had the problem.

Edit:

After some back and forth I asked if it was possible that 2 instances of the MyService class were getting created/used. @abcXYZ adding something like System.out.println("getting foo in " + System.identityHashCode(this) + " = " + foo); to the getter and setter methods which showed that there were actually 2 different instances of the class for some reason. So the JMX thread was looking at one while the web app was using the other. Ouch.