Multiple annotations of the same type on one element?

Note: This answer is partially outdated since Java 8 introduced the @Repeatable annotation (see answer by @mernst). The need for a @Foos container annotation and dedicated handling still remain though.

Two or more annotations of same type aren't allowed. However, you could do something like this:

public @interface Foos {
    Foo[] value();
}

// pre Java 8
@Foos({@Foo(bar="one"), @Foo(bar="two")})
public void haha() {}

// post Java 8 with @Repeatable(Foos.class) on @Foo
@Foo(bar="one") @Foo(bar="two")
public void haha() {}

You'll need dedicated handling of Foos annotation in code though.

Repeating annotations in Java 8

In Java 8 (released in March 2014), it is possible to write repeated/duplicate annotations.

See tutorial, Repeating Annotations.

See specification, JEP 120: Repeating Annotations.