How to mock variables in try-with-resource blocks

I am currently using junit-4.12 along with mockito-1.10. I am trying to inject mocks into try-with-resource block such as

try (InputStream inputStream = new FileInputStream("inputFile.txt") {
    ...
}

Is there a way in which I can inject mock for inputStream? I have tried declaring inputStream outside of try block as below:

InputStream inputStream;
try (inputStream = new FileInputStream("inputFile.txt") {
    ...
}

However, Java does not like this and throws error.

I am open to using any other library if I must, any help will be appreciated!

Thanks.