On 23/05/2018 21:28, Peter Levart wrote:
:
It's not an official plugin. And it seems that the Maven container is
to blame, not the plugin.
Robert Scholte is on this mailing list and may be able to comment on this.
The nonstandard ClassLoader is supplied by the container. The plugin
just uses the most direct and default API possible to instantiate
JavaScript engine:
jsEngine = new ScriptEngineManager().getEngineByName("JavaScript");
It is the environment the plugin is executing in that doesn't play
well with how system service providers are located from JDK 9 on -
namely, the nonstandard ClassLoader that delegates to system class
loader, but does not express this also in the .getParent() result. I
don't know why Maven choose this, but closer inspection reveals that
its ClassLoader does have a "parent", but it keeps it in its own field
called "parentClassLoader" and doesn't return it from .getParent().
There must be a reason for this, but I don't know that it is.
Do other parts of the JDK also use TCCL to bootstrap service lookup by
default? Isn't it unusual that ScriptEngineManager uses TCCL by default?
I wasn't involved in JSR 223 but it may have envisaged scenarios where
applications bundle scripting language implementations. This is not too
unusual and you'll find several APIs do this to allow for cases where an
application is launched in a container environment. Legacy applet and
Java EE containers have historically created a class loader per
"application" and this becomes the TCCL for the threads in that application.
-Alan
