RFR: 8364227: MBeanServer registerMBean throws NPE

[Kevin Walls]

On Wed, 30 Jul 2025 11:19:33 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

> A long-standing omission where MBeanServer.registerMBean documents exception behaviour, but we actually throw an NPE.  We should recognise a null object and return the wrapped exception we document.
> 
> This wrapping behaviour is common elsewhere in this area, e.g. unregisterMBean which checks for a null name and throws RuntimeOperationsException.
> 
> Docs:
> https://docs.oracle.com/en/java/javase/24/docs/api/java.management/javax/management/MBeanServer.html#registerMBean(java.lang.Object,javax.management.ObjectName)
> 
> Throws:
> RuntimeOperationsException - Wraps a java.lang.IllegalArgumentException: The object passed in parameter is null or no object name is specified.
> 
> 
> Current behaviour:
> 
> 
> $ java MBS_NPE.java
> Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.getClass()" because "object" is null
>         at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:296)
>         at java.management/com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:511)
>         at MBS_NPE.main(MBS_NPE.java:11)
> 
> 
> Should be changed to:
> 
> 
> $ java MBS_NPE.java
> javax.management.RuntimeOperationsException: Exception occurred trying to register the MBean
>         at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:297)
>         at java.management/com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:511)
>         at MBS_NPE.main(MBS_NPE.java:11)
>         at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
>         at java.base/java.lang.reflect.Method.invoke(Method.java:565)
>         at jdk.compiler/com.sun.tools.javac.launcher.SourceLauncher.execute(SourceLauncher.java:258)
>         at jdk.compiler/com.sun.tools.javac.launcher.SourceLauncher.run(SourceLauncher.java:138)
>         at jdk.compiler/com.sun.tools.javac.launcher.SourceLauncher.main(SourceLauncher.java:76)
> Caused by: java.lang.IllegalArgumentException: Object cannot be null
>         at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:295)
>         ... 7 more

On the CSR, my judgement was that this is superficial enough that a CSR is not necessary.  I think that fits with the CSR FAQs.

https://wiki.openjdk.org/display/csr/CSR+FAQs
Q: Under what conditions does a CSR need to be filed for a purely behavioral change?
A: "...if it is estimated enough developers or users would be sufficiently impacted by the change that it should get additional consideration or documentation. A judgment call is involved."


On the test, maybe this is an opportunity to add tests for more of those possible NPEs that get wrapped, almost none of which we test, I can look into that and update...

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PR Comment: https://git.openjdk.org/jdk/pull/26548#issuecomment-3136552231