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[jetty-dev] JDK 9 b148 including a refresh of the module system is available on

Hi Simone,

JDK 9 build b148 includes an important Refresh of the module system [1] , summary of  changes are listed here .

This refresh includes a disruptive change that is important to understand.

For those that have been trying out modules with regular JDK 9 builds then be aware that `requires public` changes to `requires transitive`. In addition, the binary representation of the module declaration (module-info.class) has changed so that you need to recompile any modules that were compiled with previous JDK 9 builds.

As things stand today in JDK 9 then you use setAccessible to break into non-public elements of any type in exported packages. However, it cannot be used to break into any type in non-exported package. The current specified behavior was a compromise for the initial integration of the module system. It is of course not very satisfactory, hence the #AwkwardStrongEncapsulation issue [2] on the JSR 376 issues list. With the updated proposal in the JSR, this refresh changes setAccessible further so that it cannot be used to break into non-public types, or non-public elements of public types, in exported packages. Code that uses setAccessible to hack into the private constructor of java.lang.invoke.MethodHandles.Lookup will be disappointed for example.

This change will expose hacks in many existing libraries and tools. As a workaround then a new command line option `--add-opens` can be used to open specific packages for "deep reflection". For example, a really popular build tool fails with this refresh because it uses setAccessible + core reflection to hack into a private field of an unmodifiable collection so that it can mutate it, facepalm! This code will continue to work as before when run with `--add-opens java.base/java.util=ALL-UNNAMED` to open the package java.util in module java.base to "all unnamed modules" (think class path).

Any help reporting issues to popular tools and libraries would be appreciated.

A debugging aid that is useful to identify issues is to run with -Dsun.reflect.debugModuleAccessChecks=true to get a stack trace when setAccessible fails, this is particularly useful when code swallows exceptions without any logging.


Rgds,Rory O'Donnell
Quality Engineering Manager
Oracle EMEA , Dublin, Ireland 

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