Remove a compile time reference to com.sun.jndi.ldap.LdapCtxFactory

[iherasymenko]

Fixes #543

com.sun.jndi.ldap.LdapCtxFactory is not supposed to be used by anyone but the 'java.naming' module in post Java 8 world.

Having the hard-reference leads to a class loading error when used with --illegal-access=deny or when simply put on module path.

java.lang.IllegalAccessError: class org.springframework.ldap.core.support.AbstractContextSource (in unnamed module @0x38952512) cannot access class com.sun.jndi.ldap.LdapCtxFactory (in module java.naming) because module java.naming does not export com.sun.jndi.ldap to unnamed module @0x38952512
	at org.springframework.ldap.core.support.AbstractContextSource.<clinit>(AbstractContextSource.java:77)

[iherasymenko]

@rwinch I would appreciate if you could provide your feedback. I did not come up with a way to cover this change with a meaningful integration test because building the project on Java 9+ will require Gradle version upgrade. However, I did test this change locally by building the library and consuming it in a project that is run with Java 15 + --illegal-access=deny flag.

[jzheaux]

Thanks, @iherasymenko! This is now merged into master.

[iherasymenko]

Thank you @jzheaux for reviewing and merging this. Do you have any idea how soon 2.3.4 will be released?

[mnhock]

Will the version 2.3.4 part of the 2.4.4 Spring Boot version? Due to the Java 16 issue?

[rosti-il]

With this change the public Class<?> getContextFactory() method may return null although the DEFAULT_CONTEXT_FACTORY is in use. This is a change of behavior. Who uses this method? If nobody uses it, could it be [1] removed or [2] return String instead of Class<?>? In both cases the type of the contextFactory field might also be changed from Class<?> to String and initialized as DEFAULT_CONTEXT_FACTORY.

I think this PR is good as a workaround that provides compatibility with recently released Java 16 to Spring LDAP 2.3.x, so please release 2.3.4 with it. Consider to do changes I proposed above in Spring LDAP 2.4.0.

[iherasymenko]

@rosti-il nice catch! Using org.springframework.util.ClassUtils.resolveClassName("com.sun.jndi.ldap.LdapCtxFactory", null); will allow to preserve the existing behavior of public Class<?> getContextFactory(). @jzheaux please let us know your thoughts on this. I can prepare a PR with these changes if you'd prefer.

[rwinch]

@iherasymenko Thanks for the offer. Can you please prepare a PR for the changes?

[iherasymenko]

@rwinch here it is #579