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
Rework classloading for launched applications so that CLI classes and
dependencies are not visible. This change allows many of the previous
hacks and workarounds to be removed.
With the exception of the 'org.springframework.boot.groovy' package
and 'groovy-all' all user required depndencies are now pulled in
via @Grab annotations.
The updated classloading algorithm has enabled the following changes:
- AetherGrapeEngine is now back in the cli project and the
spring-boot-cli-grape project has been removed. The AetherGrapeEngine
has also been simplified.
- The TestCommand now launches a TestRunner (similar in design to the
SpringApplicationRunner) and report test failures directly using
the junit TextListener. Adding custom 'testers' source to the users
project is no longer required. The previous 'double compile' for
tests has also been removed.
- Utility classes have been removed in favor of using versions from
spring-core.
- The CLI jar is now packaged using the 'boot-loader' rather than using
the maven shade plugin.
This commit also applied minor polish refactoring to a number of
classes.
Prior to this commit, the Aether-based GrapeEngine was loaded in the
same class loader as the rest of Boot. This led to Aether's and its
dependencies' types polluting the application's class path. Most
notably, this caused problems with logging as the logging framework
could be permaturely initialized.
This commit isolates AetherGrapeEngine, Aether and its dependencies
into a separate class loader. This is done by customizing the
packaging of the CLI's jar file with the internal directory housing
all of the types that will be loaded by the separate class loader.
Stephane Nicoll
Andy Wilkinson
Phillip Webb
Phillip Webb
Andy Wilkinson
Phillip Webb
Dave Syer
Dave Syer