Wrapping functions in Java sucks.

gistfile1.java

  public <A,B> Function<Function<A,B>, Function<A,B>> requiresTx() {
    return new Function<Function<A,B>, Function<A,B>>() {
      @Override
      public Function<A,B> apply(final Function<A,B> f) {
        return new Function<A,B>() {
          public B apply(final A a) { 
            return txService.required(new Callable<B>() {
              public B call() throws Exception {
                return f.apply(a);
              };
            });
          };
        };
      }
    };
  }