is ClassLoader.loadClass() supposed to work on module-info classes?
David M. Lloyd
david.lloyd at redhat.com
Wed Dec 2 15:15:09 UTC 2015
On 12/02/2015 09:05 AM, Remi Forax wrote:
> ----- Mail original -----
>> De: "David M. Lloyd" <david.lloyd at redhat.com>
>> À: jigsaw-dev at openjdk.java.net
>> Envoyé: Mercredi 2 Décembre 2015 15:52:56
>> Objet: Re: is ClassLoader.loadClass() supposed to work on module-info classes?
>> On 12/02/2015 08:46 AM, Remi Forax wrote:
>>> ----- Mail original -----
>>>> De: "Alan Bateman" <Alan.Bateman at oracle.com>
>>>> À: "Stephane Epardaud" <stef at epardaud.fr>, jigsaw-dev at openjdk.java.net
>>>> Envoyé: Mercredi 2 Décembre 2015 14:56:00
>>>> Objet: Re: is ClassLoader.loadClass() supposed to work on module-info
>>>> On 02/12/2015 11:01, Stephane Epardaud wrote:
>>>>> Just tried it and got:
>>>>> Exception in thread "main" java.lang.ClassFormatError: Illegal class
>>>>> name "com.ceylon.java9.Test" in class file module-info
>>>>> at java.lang.ClassLoader.defineClass1(java.base at 9.0/Native Method)
>>>>> java.lang.ClassLoader.defineClass(java.base at 9.0/ClassLoader.java:854)
>>>>> java.security.SecureClassLoader.defineClass(java.base at 9.0/SecureClassLoader.java:152)
>>>>> java.net.URLClassLoader.defineClass(java.base at 9.0/URLClassLoader.java:462)
>>>>> java.net.URLClassLoader.access$100(java.base at 9.0/URLClassLoader.java:75)
>>>>> java.net.URLClassLoader$1.run(java.base at 9.0/URLClassLoader.java:370)
>>>>> java.net.URLClassLoader$1.run(java.base at 9.0/URLClassLoader.java:364)
>>>>> at java.security.AccessController.doPrivileged(java.base at 9.0/Native
>>>>> java.net.URLClassLoader.findClass(java.base at 9.0/URLClassLoader.java:363)
>>>>> java.lang.ClassLoader.loadClass(java.base at 9.0/ClassLoader.java:440)
>>>>> java.lang.ClassLoader.loadClass(java.base at 9.0/ClassLoader.java:373)
>>>>> I know it works for package-info.class files, but is it supposed to work
>>>>> with module-info.class files too? Or is it just not implemented yet?
>>>> The this_class should be <internal-name>/module-info but in any case,
>>>> this isn't the way to "define" a module to the run-time. Instead modules
>>>> are defined in layers, with Layer.create the method to create a Layer.
>>> there are two issues, the first one is should a module-info be accessible
>>> at runtime as a Class and the second is that the current binary format for
>>> a module-info.class break the invariant that the name of the .class is the
>>> same as the name inside of the .class because the name used for a
>>> module-info.class is the name of the module.
>>> 1) I think module-info should not be reified to a class, defineClass should
>>> reject any .class that has a module bit set in the class file format.
>>> If we allow to create a Class from a module-info, a class loader may be
>>> able to load several module-info.class and it will be a real mess
>>> because module-info.class is not qualified in the jar file so the
>>> classloader will return the first seen.
>>> 2) In term of backward compatibility, I think i prefer that the
>>> module-info.class uses "module-info" as class name and store the name of
>>> the module inside an attribute.
>>> An already existing tool that parses the bytecode format may forget to
>>> check the class version and use the module name to do something, if
>>> the name inside the module-info is "module-info", it will be easier to
>>> diagnose because the error will report a failure on "module-info" and
>>> not on a name that can also be a package name.
>> If it's not a class, it's pretty bizarre to call it "module-info.class".
>> At this point can we admit we're bending over backwards for principles
>> that don't really add up?
> We already had this discussion, no ?
> It's a ".class" but not a java.lang.reflect.Class, i.e it's a compiled artifact of the Java platform,
> and the real question is why the file format of Java the platform is .class and not .btcd (for bytecode).
You can couch it in whatever terms you want, but it's still an ugly
duckling, and entirely self-justified. There's no good solid reason to
make this into a class file other than the social excuse "make it part
of the language/JVM".
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