Update `PropertiesLauncher` so that classes can be loaded outside of
`BOOT-INF/classes`. You can use a subdirectory, or the root directory
of an external jar (but not the parent archive to avoid issues
with agents and awkward delegation models).
Fixes gh-8480
Closes gh-8486
The main changes are:
- Switch to `loader.properties` instead of `application.properties`
- Search for `loader.properties` in `loader.home` as well as in
the classpath
- Placeholder replacements in MANIFEST.MF (using `loader.properties`
or system/env vars)
See gh-7221
Closes gh-8346
When an application is run as an executable archive with nested jars,
the application's own classes need to be able to load classes from
within the nested jars. This means that the application's classes need
to be loaded by the same class loader as is used for the nested jars.
When an application is launched with java -jar the contents of the
jar are on the class path of the app class loader, which is the
parent of the LaunchedURLClassLoader that is used to load classes
from within the nested jars. If the root of the jar includes the
application's classes, they would be loaded by the app class loader
and, therefore, would not be able to load classes from within the
nested jars.
Previously, this problem was resolved by LaunchedURLClassLoader being
created with a copy of all of the app class laoder's URLs and by
using an unconventional delegation model that caused it to skip its
parent (the app class loader) and jump straight to its root class
loader. This ensured that the LaunchedURLClassLoader would load both
the application's own classes and those from within any nested jars.
Unfortunately, this unusual delegation model has proved to be
problematic. We have seen and worked around some problems with Java
Agents (see gh-4911 and gh-863), but there are others (see gh-4868)
that cannot be made to work with the current delegation model.
This commit reworks LaunchedURLClassLoader to use a conventional
delegate model with the app class loader as its parent. With this
change in place, the application's own classes need to be hidden
from the app class loader via some other means. This is now achieved
by packaging application classes in BOOT-INF/classes (and, for
symmetry, nested jars are now packaged in BOOT-INF/lib). Both the
JarLauncher and the PropertiesLauncher (which supports the executable
jar layout) have been updated to look for classes and nested jars in
these new locations.
Closes gh-4897
Fixes gh-4868
It is sufficient for most purposes (e.g. the ones PropertieLauncher needs)
to only read the META-INF directory (not the whole file tree). So a quick
fix is to make META-INF a special case when initializing non-recursive
entries.
Fixes gh-520
