As it does not make sense to supply my current "under construction" code, I
created two Java
programs, one using reflection and one MethodHandles that behave like my
current testbed. I added
those two Java programs "TestUseViaReflection.java" (compile and run with
"7a_module_compile_and_run_TestUseViaReflection.cmd") and
"TestUseViaReflectionAndMethodHandles.java" (compile and run with
"8a_module_compile_and_run_TestUseViaReflectionAndMethodHandles.cmd") to the
zip archive and
replaced the zip-archive on Dropbox
(<https://www.dropbox.com/s/fti7camrb5hs7we/02-20180123-getPublicField.zip?dl=0>)
with the updated one.
This is the "pure reflection" version, that I would prefer,
"TestUseViaReflection.java":
import java.lang.reflect.Field;
public class TestUseViaReflection
{
public static void main (String args[]) {
mtest3.Class03A o=new mtest3.Class03A();
Class sc =o.getClass().getSuperclass(); // get superclass
mtest2.Class02A
Field field = null;
try {
field =sc.getDeclaredField("pubStaticFromClass02A"); // get
static field
}
catch (Exception e)
{
System.err.println("exception thrown in
sc.getDeclaredField(...): "+e);
e.printStackTrace();
System.exit(-1);
}
Object result=null;
try {
result=field.get(o); // get field's value
}
catch (Exception e)
{
System.err.println("exception thrown in field.get(...): "+e);
e.printStackTrace();
System.exit(-1);
}
System.out.println("o.pubStaticFromClass02A : "+result );
}
}
Running it yields:
G:\xfer\java9modules\02-20180123-getPublicField>java -cp "." --module-path
out --add-modules
mod_A,mod_B,mod_C TestUseViaReflection
exception thrown in field.get(...): java.lang.IllegalAccessException: class
TestUseViaReflection
cannot access class mtest2.Class02A (in module mod_B)
because module mod_B does not export mtest2 to unnamed module @4e04a765
java.lang.IllegalAccessException: class TestUseViaReflection cannot access
class mtest2.Class02A
(in module mod_B) because module mod_B does not export mtest2 to unnamed
module @4e04a765
at
java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:361)
at
java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:589)
at java.base/java.lang.reflect.Field.checkAccess(Field.java:1075)
at java.base/java.lang.reflect.Field.get(Field.java:416)
at TestUseViaReflection.main(TestUseViaReflection.java:23)
----------------
This is the version that tries to use MethodHandles instead,
"TestUseViaReflectionAndMethodHandles.java":
import java.lang.reflect.Field;
import java.lang.invoke.*;
public class TestUseViaReflectionAndMethodHandles
{
public static MethodHandles.Lookup lookup=MethodHandles.lookup();
public static void main (String args[]) {
mtest3.Class03A o=new mtest3.Class03A();
Class sc =o.getClass().getSuperclass(); // get superclass
mtest2.Class02A
Field field = null;
try {
field =sc.getDeclaredField("pubStaticFromClass02A"); // get
static field
}
catch (Exception e)
{
System.err.println("--> exception thrown in
sc.getDeclaredField(...): "+e);
e.printStackTrace();
System.exit(-1);
}
Object result=null;
MethodHandle mh;
try {
mh=lookup.unreflectGetter(field);
result=mh.invoke(o);
}
catch (Throwable t)
{
System.err.println("--> exception thrown in field.get(...):
"+t);
t.printStackTrace();
System.exit(-1);
}
System.out.println("o.pubStaticFromClass02A : "+result );
}
}
Running it yields:
G:\xfer\java9modules\02-20180123-getPublicField>java -cp "." --module-path
out --add-modules
mod_A,mod_B,mod_C TestUseViaReflectionAndMethodHandles
--> exception thrown in field.get(...): java.lang.IllegalAccessException:
access to public
member failed:
mtest2.Class02A.pubStaticFromClass02A/java.lang.String/getStatic, from
TestUseViaReflectionAndMethodHandles (unnamed module @4e04a765)
java.lang.IllegalAccessException: access to public member failed:
mtest2.Class02A.pubStaticFromClass02A/java.lang.String/getStatic, from
TestUseViaReflectionAndMethodHandles (unnamed module @4e04a765)
at
java.base/java.lang.invoke.MemberName.makeAccessException(MemberName.java:914)
at
java.base/java.lang.invoke.MethodHandles$Lookup.checkAccess(MethodHandles.java:2193)
at
java.base/java.lang.invoke.MethodHandles$Lookup.checkField(MethodHandles.java:2143)
at
java.base/java.lang.invoke.MethodHandles$Lookup.getDirectFieldCommon(MethodHandles.java:2355)
at
java.base/java.lang.invoke.MethodHandles$Lookup.getDirectFieldNoSecurityManager(MethodHandles.java:2350)
at
java.base/java.lang.invoke.MethodHandles$Lookup.unreflectField(MethodHandles.java:1863)
at
java.base/java.lang.invoke.MethodHandles$Lookup.unreflectGetter(MethodHandles.java:1854)
at
TestUseViaReflectionAndMethodHandles.main(TestUseViaReflectionAndMethodHandles.java:27)
----------------
However the Java program "TestUse_mtest3_Class03A.java" compiles and runs
successfully:
Compiling the modules and then using them in the following Java program (via
the CLASSPATH) works,
here the source:
TestUse_mtest3_Class03A.java
public class TestUse_mtest3_Class03A
{
public static void main (String args[]) {
mtest3.Class03A o=new mtest3.Class03A();
System.out.println("o.pubStaticFromClass02A :
"+o.pubStaticFromClass02A );
System.out.println("o.pubFromClass02A :
"+o.pubFromClass02A );
System.out.println("o: "+o+", o.getMyClassName():
"+o.getMyClassName());
}
}
Compiling the above program and running it yields:
o.pubStaticFromClass02A : static-mtest2.Class02A
o.pubFromClass02A : instance-mtest2.Class02A
o: mtest3.Class03A@5afa04c, o.getMyClassName(): via:
this=[mtest3.Class03A@5afa04c],
getMyClassName()=[class-mtest1.Class01A]
----------------
Maybe I miss something obvious.
---rony
On 23.01.2018 19:17, Rony G. Flatscher wrote:
> Was asked off-line for a zip-archive for convenience, hence I created a zip
> archive and put it on
> Dropbox. Here the link to get the zip-archive:
> <https://www.dropbox.com/s/fti7camrb5hs7we/02-20180123-getPublicField.zip?dl=0>.
> Just unzip, go
> into the <02-20180123-getPublicField> directory and run (on Windows)
> "1_compile.cmd", then either
> "5a_module_compile_and_run_TestUse_mtest3_Class03A.cmd" or
> "5b_classpath_compile_and_run_TestUse_mtest3_Class03A.cmd". Adapting the
> scripts to Unix should be
> straight forward.
>
> Being formally an OpenJDK contributor there should be no legal problems.
>
> ---rony
>
>
> On 23.01.2018 18:32, Rony G. Flatscher wrote:
>> Oh, forgot the scripts to compile and run (these are under Windows):
>>
>> Assuming that the sources of "mod_A", "mod_B" and m"od_C" are located in
>> "src", the compilation
>> result should be placed into "out" here the compile script:
>>
>> rd out /s /q && md out
>>
>> @echo compiling module mod_A
>> dir src\mod_A\*java /s /b > mod_A_source_files.txt
>> type mod_A_source_files.txt
>> javac -d out\mod_A @mod_A_source_files.txt
>>
>> @echo compiling module mod_B
>> dir src\mod_B\*java /s /b > mod_B_source_files.txt
>> type mod_B_source_files.txt
>> javac --module-path out -d out\mod_B @mod_B_source_files.txt
>>
>> @echo compiling module mod_C
>> dir src\mod_C\*java /s /b > mod_C_source_files.txt
>> type mod_C_source_files.txt
>> javac --module-path out -d out\mod_C @mod_C_source_files.txt
>>
>> Assuming that "TestUse_mtest3_Class03A.java" is located in the directory
>> that contains the "out"
>> subdirectory:
>>
>> del TestUse_mtest3_Class03A.class
>> javac -cp "." --module-path out --add-modules mod_A,mod_B,mod_C
>> TestUse_mtest3_Class03A.java
>>
>> java -cp "." --module-path out --add-modules mod_A,mod_B,mod_C
>> TestUse_mtest3_Class03A
>>
>> ---rony
>>
>>
>> On 23.01.2018 15:52, Rony G. Flatscher wrote:
>>> Given three modules (sources at the end) where
>>>
>>> * "mod_A" exports its package "mtest1", to everyone
>>> * "mod_B" requires "mod_A" and exports its package "mtest2" to "mod_C"
>>> * "mod_C" requires "mod_B" and exports its package "mtest3" to everyone
>>>
>>> "mod_B"'s class "mtest2.Class02A" defines two public fields, one static
>>> ("pubStaticFromClass02A")
>>> and one an instance ("pubFromClass02") one.
>>>
>>> Compiling the modules and then using them in the following Java program
>>> (via the CLASSPATH) works,
>>> here the source:
>>>
>>> TestUse_mtest3_Class03A.java
>>>
>>> public class TestUse_mtest3_Class03A
>>> {
>>> public static void main (String args[]) {
>>> mtest3.Class03A o=new mtest3.Class03A();
>>> System.out.println("o.pubStaticFromClass02A :
>>> "+o.pubStaticFromClass02A );
>>> System.out.println("o.pubFromClass02A :
>>> "+o.pubFromClass02A );
>>> System.out.println("o: "+o+", o.getMyClassName():
>>> "+o.getMyClassName());
>>> }
>>> }
>>>
>>> Compiling the above program and running it yields:
>>>
>>> o.pubStaticFromClass02A : static-mtest2.Class02A
>>> o.pubFromClass02A : instance-mtest2.Class02A
>>> o: mtest3.Class03A@5afa04c, o.getMyClassName(): via:
>>> this=[mtest3.Class03A@5afa04c],
>>> getMyClassName()=[class-mtest1.Class01A]
>>>
>>> Here is a 1:1 transcription from the above Java program to Rexx which uses
>>> Java reflection to
>>> achieve the same:
>>>
>>> test.rex
>>>
>>> o=.bsf~new("mtest3.Class03A") -- create Java object
>>> say "o~pubStaticFromClass01A:" o~pubStaticFromClass02A
>>> say "o~pubFromClass01A :" o~pubFromClass02A
>>> say "o:" o "o~getMyClassName:" o~getMyClassName
>>>
>>> ::requires BSF.CLS -- direct interpreter to load Java bridge
>>>
>>> Running the Rexx program yields the following reflection error:
>>>
>>> // // -> -> RexxReflectJava9.processField(): EXCEPTION in GET-operation:
>>> tmpField="pubStaticFromClass02A" exception:
>>> "java.lang.IllegalAccessException: class
>>> org.rexxla.bsf.engines.rexx.RexxReflectJava9 cannot access class
>>> mtest2.Class02A (in module
>>> mod_B) because module mod_B does not export mtest2 to unnamed module
>>> @51c8530f"
>>>
>>> The reflection code currently
>>>
>>> * gets the type from the Java object ("mtest3.Class03A") and tests
>>> whether the package "mtest3" is
>>> exported (it is),
>>> * looks for all declaredFields and finds none, so it gets the superclass
>>> "mtest2.Class02A",
>>> * looks for all declaredFields and locates the Field named
>>> "pubStaticFromClass02A" and invokes the
>>> Field's get method, supplying the Java object (an instance of class
>>> mtest3.Class03A) which
>>> causes an IlleagalAccessException.
>>>
>>> Although it is true that "mod_B" is not exported to the unnamed module it
>>> is still the case that
>>> "mod_C" is exported (and class "mtest3.Class03A" can be accessed), such
>>> that all public members in
>>> its superclasses should be accessible via reflection, even in the case that
>>> a public member resides
>>> in a module that is not exported to the reflector from the unnamed module?
>>>
>>> The reflective code would be able to assess that the supplied object is
>>> from an exported type and
>>> hence allow the get access in this case for reflected members in its
>>> superclasses, like it seems the
>>> Java compiler allows for.
>>>
>>> ---rony
>>>
>>> Here are the contents of the module directories in source:
>>>
>>>
>>> ---------------------------------------------------------------------------
>>>
>>> mod_A/module-info.java
>>>
>>> module mod_A { exports mtest1; }
>>>
>>> mod_A/mtest1/Class01A.java
>>>
>>> package mtest1;
>>>
>>> abstract public class Class01A
>>> {
>>> protected static String myClassName =
>>> "class-mtest1.Class01A";
>>> }
>>>
>>>
>>> ---------------------------------------------------------------------------
>>>
>>> mod_B/module-info.java
>>>
>>> module mod_B {
>>> requires mod_A;
>>> exports mtest2 to mod_C;
>>> }
>>>
>>> mod_B/mtest2/Class02A.java
>>>
>>> package mtest2;
>>>
>>> public class Class02A extends mtest1.Class01A
>>> {
>>> public static String
>>> pubStaticFromClass02A="static-mtest2.Class02A";
>>> public String pubFromClass02A
>>> ="instance-mtest2.Class02A";
>>>
>>> public String getMyClassName()
>>> {
>>> return "via: this=["+this+"],
>>> getMyClassName()=["+myClassName+"]";
>>> }
>>> }
>>>
>>>
>>> ---------------------------------------------------------------------------
>>>
>>> mod_C/module-info.java
>>>
>>> module mod_B {
>>> requires mod_A;
>>> exports mtest2 to mod_C;
>>> }
>>>
>>> mod_C/mtest3/Class03A.java
>>>
>>> package mtest3;
>>>
>>> public class Class03A extends mtest2.Class02A
>>> {
>>> }
>>>
>>>
>>> --------------------------------------------------------------------------
