ghurtchu/fluentry

:policeman::oncoming_police_car: Manage unchecked exceptions functionally.

An attempt to port scala.util.Try to Java.

The main class is called Try.

Try has a few overloaded static constructors for instantiating lazy computations which is called Try.of().

Try instance may be constructed via one of these five arguments:

• Runnable
• Consumer<T> with arg,
• Supplier<T>,
• Function<T, V> with arg,
• BiFunction<T, U, V> with two args

Try has two sub-classes: Success<T> which holds the successful value and Failure which holds the exception.

Try may be used in different ways, so without further ado let's see the examples below:

problem description: try getting the element from the list, if it fails return stringified 0, or else return the stringified square of the success value.

solution with pure java:

   public static String getAndThenDoubleAndThenStringify(List<Integer> list, int index) {
       String result;
       try {
           int number = list.get(index);
           result = String.valueOf(number * 2);
       } catch (Exception e) {
           result = "0";
       }
       return result;
   }

solution with fluenTry:

   public static String getAndThenDoubleAndThenStringify(List<Integer> list, int index) {
       return Try.of(list, index, List::get).map(n -> n * 2).fold(String::valueOf, "0");
   }

Here is a Failed computation which returns Failure(ArithmeticException) instead of blowing up the calling stack by throwing an exception and succeeds with pure value with the help of fold combinator:

   double result = Try.of(() -> Math.random() * 2 * 5)
           .flatMap(n -> Try.of(() -> n + 1))
           .flatMap(n -> Try.of(() -> 55 / 0)) // This is where the `Success` turns into `Failure`
           .map(Math::sqrt)
           .fold(Function.identity(), 0.0); // but with the help of `fold` we turn that into pure value

Let's see another example:

problem description: try to parse json string into Person instance, if succeeds return true or else return false.

solution with pure java:

   public static Optional<Person> parseJson(String json) {
       var jsonParser = new JsonParser<Person>();
       Optional<Person> result;
       try {
           result = Optional.of(jsonParser.fromJson(json));
       } catch (JsonParsingException jpe) {
           result = Optional.empty();
       }
       return result;
   }

solution with fluenTry - takes a string argument and the Function<T, V> instance as a second argument, finally calles toOptional() which converts the Try<T> into Optional<T>:

   public static Optional<Person> parseJson(String json) {
       var parser = new JsonParser<Person>();
       return Try.of(json, parser::fromJson).toOptional();
   }

Let's see something related to java Enums:

problem description: Write a method on Weekend enum which returns true of the passed string is a Weekend day or else return false.

solution with pure java:

    public enum Weekend {
    
        SATURDAY,
        SUNDAY;

        public static boolean isWeekend(String day) {
            try {
                String normalized = day.trim().toUpperCase();
                Weekend.valueOf(normalized);
                return true;
            } catch (IllegalArgumentException iae) {
                return false;
            }
        }

   }

with fluenTry: - takes a Supplier<String> as an argument, then maps and finally folds to either true or false:

    public enum Weekend {
    
        SATURDAY,
        SUNDAY;

        public static boolean isWeekend(String day) {
            return Try.of(() -> day.trim().toUpperCase()).map(Weekend::valueOf).fold(d -> true, false);
        }
   }