Summary

Disable M-Lets by default, and require a System Property com.sun.jmx.enableMLetRegistration be set to true, in order for them to be usable.

Problem

M-Lets are a feature with no sign of usage, and a JEP is in process (JDK-8285724) for their deprecation and removal.

It would be possible for the JEP to proceed and a user of M-Lets to be unaware of the impending deprecation and removal. Requiring some action ensures that any existing user is aware, as they need to make a simple change to continue using the feature.

Solution

Refusal to register an M-Let without a new System Property being set.

Specification

javax.management.loading.MLet will throw UnsupportedOperationException from its preRegister method, unless the System Property com.sun.jmx.enableMLetRegistration is set to "true".

Draft PR: https://github.com/openjdk/jdk/pull/9852