https://issues.apache.org/bugzilla/show_bug.cgi?id=55317
Bug ID: 55317
Summary: Make o.a.c.l.WebappClassLoader Instrumentable
Product: Tomcat 7
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Catalina
Assignee: dev@tomcat.apache.org
Reporter: nicho...@nicholaswilliams.net
Most application servers provide a mechanism whereby web applications can
instrument class bytecode. This is normally in the form of two or three
instrumentation methods on the ClassLoader implementation responsible for web
application class loading. Spring Framework, for example, provides a way to
automatically detect and use the various instrumentable ClassLoaders provided
by different application servers. However, since Tomcat's
o.a.catalina.loader.WebappClassLoader is not instrumentable, Spring cannot use
it directly. Instead, it provides a class that extends WebappClassLoader to
implement the instrumentation. Users must place this special
spring-instrument-tomcat.jar file in $TOMCAT_HOME/lib and put a loader
declaration in META-INF/context.xml in order to get this to work--rather a pain
in the rear.
Spring's changes in the extended WebappClassLoader are really very trivial and
involve only 2 classes: a helper class called WeavingTransformer [1] and the
extended TomcatInstrumentableClassLoader [2]. I intend to port these changes to
Tomcat for Tomcat 7 and 8 and submit a patch.
However, before I get started I needed to get two answers from the community:
1) Is there any objection to such a simple addition to WebappClassLoader? I
think it would be an easy-but-big improvement to Tomcat.
2) What steps do I need to take to get this Spring code officially "donated" to
Tomcat so that all legal requirements are met? The code is licensed Apache 2.0,
so that at least should make it easier.
[1]
https://github.com/SpringSource/spring-framework/blob/master/spring-instrument-tomcat/src/main/java/org/springframework/instrument/classloading/WeavingTransformer.java
[2]
https://github.com/SpringSource/spring-framework/blob/master/spring-instrument-tomcat/src/main/java/org/springframework/instrument/classloading/tomcat/TomcatInstrumentableClassLoader.java
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