Status: New
Owner: ----
New issue 736 by pepst...@google.com: @Singleton annotation on get() method
of a Provider class shoudln't be silently ignored
http://code.google.com/p/google-guice/issues/detail?id=736
Putting the @Singleton annotation on a Provider class causes Guice to use
the same instance of that provider every time it wants to create an
instance. This can be useful, but what if you want the get method to be
called just once? Of course you can specify this in the module with
bind(Foo.class).to(FooProvider.class).in(Singleton.class);
I was thinking I could also specify this by annotating the get() method in
my Provider class with @Singleton, but this doesn't work. The annotation is
allowed on methods, but that seems to be for Provider methods. When applied
to the get() method on a Provider class, it doesn't seem to have any
effect. I think it should either make it a singleton or throw an exception
to make it clear that it's not working.
Code to help make this clear:
public class Experiment {
public static void main(String[] args) {
Injector injector = Guice.createInjector(new MyModule());
System.out.println(injector.getInstance(Integer.class));
System.out.println(injector.getInstance(Integer.class));
}
private static class MyModule extends AbstractModule {
@Override protected void configure() {
bind(Integer.class).toProvider(IntegerProvider.class);
}
}
@Singleton private static class IntegerProvider implements
Provider<Integer> {
int i = 0;
@Singleton @Override public Integer get() {
return i++;
}
}
}
This code emits 0 and then 1, where I was hoping it'd emit two 0's.
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