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From Jochen Theodorou <blackd...@gmx.org>
Subject JDK9 and the problem of @Grab
Date Fri, 26 Aug 2016 10:28:30 GMT
Hi all,

with the oncoming of JDK9 we are facing a problem with @Grab, which is 
that there is no URLClassLoader to hook into anymore by default. 
Actually that was never a guarantee, just worked in almost all of the 
scenarios of interest.

>  @Grab(group='commons-lang', module='commons-lang', version='2.4')
>  import org.apache.commons.lang.WordUtils
>  println "Hello ${WordUtils.capitalize('world')}"


There are two basic flavors to @Grab, which is using it with a source 
file and using it with a precompiled file. In both cases the @Grab would 
download dependencies and try to give the executing environment those 
dependencies.

In case of a source file, we hook into the compiler to do the downloads 
as well as change the static constructor of the class. So we ensure we 
can compile the file and since we have full control over the execution 
environment in this case we can also ensure all the libraries are 
available before the class is loaded by the JVM.

In the precompiled case, for example as a testcase, we do not have full 
control over the environment and with JDK9 there might not be a single 
URLClassloader we can use anymore. Furthermore here is a limitation of 
@Grab, which is that the grabbed classes cannot be used in any of the 
signatures of the class.

So now the question is what we want to do. The most simple version would 
be to ditch the precompiled version. If we want to keep it like is, we 
will have to add JDK9 specific code handling layers and modules.

What do you think?

bye Jochen

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