Update docs and archery tester for arrow-memory modules

Update the command-line in the docs and the archery java tester
to allow exposing reflection on unsafe on the org.apache.arrow.memory.core
module

dev/archery/archery/integration/tester_java.py

@@ -40,7 +40,7 @@ def load_version_from_pom():
 _JAVA_OPTS = [
     "-Dio.netty.tryReflectionSetAccessible=true",
     "-Darrow.struct.conflict.policy=CONFLICT_APPEND",
-    "--add-opens=java.base/java.nio=ALL-UNNAMED",
+    "--add-opens=java.base/java.nio=org.apache.arrow.memory.core,ALL-UNNAMED",
     # GH-39113: avoid failures accessing files in `/tmp/hsperfdata_...`
     "-XX:-UsePerfData",
 ]
@@ -247,7 +247,8 @@ def __init__(self, *args, **kwargs):
         if 'Unrecognized option: --add-opens' not in proc.stderr:
             # Java 9+
             self._java_opts.append(
-                '--add-opens=java.base/java.nio=ALL-UNNAMED')
+                '--add-opens=java.base/java.nio='
+                'org.apache.arrow.memory.core,ALL-UNNAMED')
 
     def _run(self, arrow_path=None, json_path=None, command='VALIDATE'):
         cmd = (

docs/source/java/install.rst

@@ -33,14 +33,14 @@ Java modules are compatible with JDK 8 and above.
 Currently, JDK 8, 11, 17, and 21 are tested in CI.
 
 When using Java 9 or later, some JDK internals must be exposed by
-adding ``--add-opens=java.base/java.nio=ALL-UNNAMED`` to the ``java`` command:
+adding ``--add-opens=java.base/java.nio=org.apache.arrow.memory.core,ALL-UNNAMED`` to the ``java`` command:
 
 .. code-block:: shell
 
    # Directly on the command line
-   $ java --add-opens=java.base/java.nio=ALL-UNNAMED -jar ...
+   $ java --add-opens=java.base/java.nio=org.apache.arrow.memory.core,ALL-UNNAMED -jar ...
    # Indirectly via environment variables
-   $ env _JAVA_OPTIONS="--add-opens=java.base/java.nio=ALL-UNNAMED" java -jar ...
+   $ env _JAVA_OPTIONS="--add-opens=java.base/java.nio=org.apache.arrow.memory.core,ALL-UNNAMED" java -jar ...
 
 Otherwise, you may see errors like ``module java.base does not "opens
 java.nio" to unnamed module``.