Use cases for java.lang.Module.addExports

Alan Bateman Alan.Bateman at
Mon Dec 12 06:53:02 UTC 2016

On 12/12/2016 06:34, David Holmes wrote:

> Does addExports only affect reflective access to the module, or does 
> it change all access? I'm trying to determine what the set of actions 
> X will be such that:
> try {
>   <X>;
> }
> catch (<some exception indicating X failed due to lack of export>) {
>   execute( () -> mod.addExports(...)); // address the problem
>   <X>;  // now it succeeds
> } 
It updates the module to export the package so that public types in that 
package are accessible to bytecode, code reflection, also method handles.

As to what <X> is then it might be an access from bytecode (maybe 
generated code or just a mismatch between the compile time and run time 
environments that leads to IllegalAccessError).

More likely then <X> is using core reflection and an access check with 
Constructor::newInstance, Method::invoke or Field::set fails with 
IllegalAccessException. The retry in your example will succeed (assuming 
the package is now exported to at least the caller and access is 
otherwise allowed by the class/member modifiers). <X> could be something 
using method handles too, say where a Lookup::findXXXX fails 


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