The sibling comments point out some good points about your general critique, but it's worth noting your code isn't really "equivalent"; almost everything you chopped was a datatype declaration, which isn't required in Java any more than in Ruby:

      @GET
      public Map<String,String> greet(@PathParam("name") String name) {
        return singletonMap( "content", "Hello, " + name );
      }

I like both of these systems, and Java is undeniably the more verbose language, but this framework really isn't an egregious example of that.