Using ServiceLoader with modules

[Alex Buckley]

// cc'ing the list because best practices should be public, and
// because it's easier to refer people to it in five years time

Hi Christian,

On 10/14/2019 12:16 PM, Christian Stein wrote:
>   just read your mail and was wondering if this extrapolation is correct:
> 
>     A module that does not export any package should never need to
>     declare a "requires" as transitive.

Some qualification needed, I think. There are (at least) two kinds of 
"top level" module that commonly have no `exports` clauses:

1. An "application module" intended to be launched (`java -m bizapp`) 
rather than programmed against. I agree that this kind of module should 
not use `requires transitive`.

2. An "aggregator module" intended to present a facade composed from the 
APIs of other modules. For example, the `java.se` module has no 
`exports`, but makes good use of `requires transitive`. (See 
http://hg.openjdk.java.net/jdk/jdk/file/tip/src/java.se/share/classes/module-info.java.)

> For example, I should remove all `transitive` modifiers from this module 
> 
> module org.junit.platform.console {
>    requires transitive org.apiguardian.api;
>    requires transitive org.junit.platform.reporting;
>    provides java.util.spi.ToolProvider
>        with org.junit.platform.console.ConsoleLauncherToolProvider;
> }

This "console" module certainly looks like #1 rather than #2.

Alex