Jigsaw EA feedback for elasticsearch

[Peter Levart]

Hi Robert,

On 09/11/2015 10:58 PM, Robert Muir wrote:
> On Fri, Sep 11, 2015 at 6:09 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
>> I'm not sure that I understand the issue here but just to say that the
>> com.sun.management API is a documented/supported API and it exported by
>> module jdk.management:
>>
>> $ java -listmods:jdk.management
>>
>> jdk.management at 9.0
>>    requires public java.management
>>    requires mandated java.base
>>    exports com.sun.management
>>    conceals com.sun.management.internal
>>    provides sun.management.spi.PlatformMBeanProvider with
>> com.sun.management.internal.PlatformMBeanProviderImpl
>>
> Here is code that fails:
>
> import java.lang.reflect.*;
> import java.lang.management.*;
>
> public class test {
>    public static void main(String args[]) throws Exception {
>      OperatingSystemMXBean osMxBean =
> ManagementFactory.getOperatingSystemMXBean();
>      Method getTotalPhysicalMemorySize =
> osMxBean.getClass().getMethod("getTotalPhysicalMemorySize");
>      getTotalPhysicalMemorySize.setAccessible(true);
>      System.out.println(getTotalPhysicalMemorySize.invoke(osMxBean));
>    }
> }
>
> Exception in thread "main"
> java.lang.reflect.InaccessibleObjectException: Unable to make member
> of class com.sun.management.internal.OperatingSystemImpl accessible:
> module jdk.management does not export com.sun.management.internal to
> <unnamed module @5f375618>
>      at sun.reflect.Reflection.throwInaccessibleObjectException(java.base at 9.0/Reflection.java:462)
>      at java.lang.reflect.AccessibleObject.checkCanSetAccessible(java.base at 9.0/AccessibleObject.java:194)
>      at java.lang.reflect.AccessibleObject.setAccessible(java.base at 9.0/AccessibleObject.java:157)
>      at test.main(test.java:8)

I guess there will be lots of similar issues discovered in various 
codebases when trying to run them with jigsaw. The problem of the above 
code is that it uses reflection to look up the optional method on the 
implementation class of the object (and that class is in some internal 
package, not exported and inaccessible to other modules) instead of 
looking it up on the public API class (the interface). You get two 
different methods that way - one is accessible and the other is not, but 
invoking either of them should be equivalent, since the dispatch is 
always virtual. So the correct way to "test" whether the method exists 
(maybe because it has been added on a praticular version of the 
platform) and then to invoke it is the following:

public class test {
   public static void main(String args[]) throws Exception {
     Method getTotalPhysicalMemorySize = 
OperatingSystemMXBean.class.getMethod("getTotalPhysicalMemorySize");
     OperatingSystemMXBean osMxBean = 
ManagementFactory.getOperatingSystemMXBean();
     System.out.println(getTotalPhysicalMemorySize.invoke(osMxBean));
   }
}


And you don't even need to set it Method.setAccessible(true), since both 
the interface and method are public.


Regards, Peter