On 13/11/2015 17:48, Rafael Winterhalter wrote:
Hi Alan,
thanks for your quick answer. I am less worried about the generated
code then I am about the generation process.
For example, a ClassFileTransformer might want to instrument all
classes that implement a certain interface. For this, the transformer
needs to parse the provided class file, extract the interfaces and
locate their class files and so forth in order to resolve the type
hierarchy. For this, it is now possible to query the ClassLoader which
is an argument provided to the transformer. I do not know how I would
access the module at this point or get hold of the class file.
I assume you know this but if you have the Instrumentation object then
you can invoke getAllLoadedClasses and filter this to the set of classes
that implement the interface. Then call retransformClasses with this set
(as an array) and your ClassFileTransformer should be invoked with the
Class<?> + class bytes for each of these classes. This puts the onus on
the VM to reconstitute the class bytes, no need for you to attempt to
locate the .class file (which may not exist of course). It also allows
multiple agents to work together.
Also, I would expect that a Java agent that worked in Java 8 would
also work in Java 9. If I had to use Java 9 APIs in order to patch my
application, I would be required to offer two versions of my library,
one for Java 9+ and one for Java 8-. That would be unfortunate.
Existing java agents that are instrumenting code on the class path
should continue to work as before. These agents are oblivious to modules
but in many cases will be able to instrument code in named modules too.
The VM is providing some "readability for free" to keep existing
instrumentation agents working. Beyond these cases then I expect agents
will need to become module aware because they are instrumenting code in
ways that interacts with modules and access checks. The current builds
don't have these APIs yet. As to making use of newer APIs then it might
add a bit of complexity to these agents or maybe to their how they are
built.
-Alan
