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Konstantin,
On 3/6/18 8:26 PM, Konstantin Kolinko wrote:
> 2018-03-06 18:43 GMT+03:00 Christopher Schultz
> <ch...@christopherschultz.net>:
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>>
>> All,
>>
>> I think I already know the answer to this question, but I'm going
>> to ask anyway in case it helps others understand what's going
>> on.
>>
>> I have a custom MBean for a loadable-object in my web
>> application. This is an object that lives in the
>> application-scope and needs to be periodically re-loaded from our
>> relational database when we add new data to it.
>>
>> The bean looks like this:
>>
>> public static class ReloadableObjectBean implements
>> ReloadableObjectBeanMBean { private ReloadableObject _rlo;
>> private Date _loadTime;
>>
>> public ReloadableObjectBean() { _rlo = null; _loadTime = null; }
>>
>> public ReloadableObjectBean(ReloadableObject dxe) { _loadTime =
>> new Date(); _rlo = dxe; }
>>
>> @Override public int getItemCount() { return
>> _rlo.getItems().size(); }
>>
>> protected Date getLoadTimeInternal() { return _loadTime; }
>>
>> @Override public Date getLoadTime() { return
>> (Date)getLoadTimeInternal().clone(); }
>>
>> @Override public void reload() throws ReloadableObjectException,
>> ServiceException { ReloadableObject rlo =
>> ReloadableObjectHelper.newReloadableObject(); _loadTime = new
>> Date(); _rlo = rlo; } }
>>
>> This is an inner class defined in one of my
>> ServletContextListeners, and it's inserted into the MBeanServer
>> like this:
>>
>> ReloadableObject rlo =
>> ReloadableObjectHelper.newReloadableObject();
>>
>> try { MBeanServer mbs = getServer(); ObjectName objectName = new
>> ObjectName("com.chadis:type=ReloadableObject");
>>
>> if(mbs.isRegistered(objectName))
>> mbs.unregisterMBean(objectName);
>>
>> mbs.registerMBean(new ReloadableObjectBean(rlo), objectName) ; }
>> catch (MBeanException mbe) { logger.warn("Cannot register MBean",
>> mbe); } catch (InstanceAlreadyExistsException iaee) {
>> logger.warn("Cannot register MBean", iaee); } catch
>> (NotCompliantMBeanException ncme) { logger.warn("Cannot register
>> MBean", ncme); } catch (MalformedObjectNameException mone) {
>> logger.warn("Cannot register MBean", mone); } catch
>> (InstanceNotFoundException infe) { logger.warn("Cannot
>> de-register MBean", infe); }
>>
>> application.setAttribute("reloadbleObject", rlo);
>>
>> Everything goes well until I try to invoke the "reload" operation
>> on this MBean from a JMX client, where I get
>> ClassNotFoundException:
>>
>> 2018-03-06 10:26:07,271 [RMI TCP Connection(1)-169.254.211.40]
>> FATAL ReloadableObjectHelper- Could not load ReloadableObject:
>> ServiceException: Cannot obtain database connection at
>> ReloadableObjectHelper.getConnection(ReloadableObjectHelper.java:147
>>
>>
)
>> at
>> ReloadableObjectHelper.newDiagnosisEngine(ReloadableObjectHelper.java
:55
>>
>>
)
>> at
>> InitListener$ReloadableObjectBean.reloadEngine(InitListener.java:159
>>
>>
)
>> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>> at
>> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
jav
>>
>>
a:62)
>> .... Caused by: Caused by:
>> javax.naming.NoInitialContextException: Cannot instantiate class:
>> org.apache.naming.java.javaURLContextFactory [Root exception is
>> java.lang.ClassNotFoundException:
>> org.apache.naming.java.javaURLContextFactory] at
>> javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:6
74)
>>
>>
at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:31
>> 3) at javax.naming.InitialContext.init(InitialContext.java:244)
>> at javax.naming.InitialContext.<init>(InitialContext.java:192) at
>> ReloadbleObjectHelper.getConnection(ReloadableObjectHelper.java:136)
>>
>>
... 39 more
>> Caused by: java.lang.ClassNotFoundException:
>> org.apache.naming.java.javaURLContextFactory at
>> java.net.URLClassLoader.findClass(URLClassLoader.java:381) at
>> java.lang.ClassLoader.loadClass(ClassLoader.java:424) at
>> sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331) at
>> java.lang.ClassLoader.loadClass(ClassLoader.java:357) at
>> java.lang.Class.forName0(Native Method) at
>> java.lang.Class.forName(Class.java:348) at
>> com.sun.naming.internal.VersionHelper12.loadClass(VersionHelper12.jav
a:7
>>
>>
2)
>> at
>> com.sun.naming.internal.VersionHelper12.loadClass(VersionHelper12.jav
a:6
>>
>>
1)
>> at
>> javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:6
72)
>>
>>
... 43 more
>>
>>
>> The error I get on VisualVM (my JMX client, here) is that it
>> can't load my ServiceException class -- one that is defined only
>> within the web application.
>>
>> I suspect the problem is that the thread's context class loader
>> (TCCL) is set to Tomcat's ClassLoader, since the request is being
>> handled by Tomcat's internal JMX server. If I were to invoke this
>> operation via the Manager's JMXProxyServlet, I'd probably be
>> dealing with the Manager's WebappClassLoader, instead, but the
>> problem would be the same: those ClassLoaders are unaware of my
>> application's classes.
>>
>> I *believe* the solution is to change the TCCL in this "reload"
>> method, but that means I'll need to capture the TCCL during the
>> invocation of the MBean itself and hang on to it... something
>> like this:
>>
>> ClassLoader originalCL =
>> Thread.currentThread().getContextClassLoader(); ReloadableObject
>> rlo = ReloadableObjectHelper.newReloadableObject();
>>
>> try { MBeanServer mbs = getServer(); ObjectName objectName = new
>> ObjectName("com.chadis:type=ReloadableObject");
>>
>> if(mbs.isRegistered(objectName))
>> mbs.unregisterMBean(objectName);
>>
>> mbs.registerMBean(new ReloadableObjectBean(rlo, originalCL),
>> objectName); }
>>
>> Then, later, in the reload() method:
>>
>>
>> @Override public void reload() throws ReloadableObjectException,
>> ServiceException { ClassLoader tccl =
>> Thread.currentThread().getContextClassLoader();
>>
>> try { Thread.currentThread().setContextClassLoader(originalCL) ;
>>
>> ReloadableObject rlo =
>> ReloadableObjectHelper.newReloadableObject(); _loadTime = new
>> Date(); _rlo = rlo; } finally {
>> Thread.currentThread().setContextClassLoader(tccl); } }
>>
>> Does that sound about right?
>>
>> I'll probably want to future-proof it by wrapping those calls
>> into PrivilegedActions, etc. but is this the right approach for
>> what I'm trying to do, here? Or am I missing something?
>>
>
> From those error messages, it looks like your code does a JNDI
> lookup.
Yes.
> And the lookup fails with a NamingException (a
> javax.naming.NoInitialContextException to be specific, but that is
> just a detail).
>
> A JNDI tree is local to a web application. Each web application has
> an independent JNDI tree. Selecting the correct one uses TCCL as
> the key.
That's what I thought. So, I just have to play with the TCCL.
> So if you TCCL class loader is not set correctly, you won't be able
> to access JNDI.
>
> If you are interested in implementation details, see
> org.apache.naming.SelectorContext
> org.apache.naming.ContextBindings
> org.apache.naming.java.javaURLContextFactory
>
>
> On the question on what is the best way to change and restore
> TCCL: Current code uses a helper API method, StandardContext.bind()
> / unbind().
This bean is being defined by my application and loaded from within
it. I'd prefer not to have a compile-time dependency on Tomcat itself.
- -chris
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