functional-reactive
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Utility Functions

String, Stream, Exception, Converting and SystemProperties helpers.

The com.svenruppert.functional package collects small, focused utility classes. Each one is an interface of static methods — no instances, no state.

StreamFunctions

static <T> Function<Predicate<T>, Function<Stream<T>, Stream<T>>> streamFilter();

Curried filter so you can build stream pipelines without needing the stream yet:

Function<String, Predicate<Car>> brandFilter = brand -> car -> car.brand().equals(brand);

Function<Predicate<Car>, Function<Stream<Car>, Stream<Car>>> sf = StreamFunctions.streamFilter();

sf.apply(brandFilter.apply("BMW"))
  .apply(carRepository.stream())
  .forEach(System.out::println);

Often combined with andThen for fully declarative pipelines:

brandFilter
    .andThen(StreamFunctions.streamFilter())
    .apply("BMW")
    .apply(carRepository.stream());

ExceptionFunctions

static Function<Exception, String>                       message();
static Function<Exception, Stream<StackTraceElement>>    toStackTraceStream();

message() is what every Checked* interface uses internally to render a failure reason — falling back to the simple class name when getMessage() is null.

String reason = ExceptionFunctions.message().apply(ex);

ExceptionFunctions.toStackTraceStream()
    .apply(ex)
    .limit(5)
    .forEach(System.err::println);

Converting

static <T> Function<T, Result<String>>  convertToString();
static <T> Function<T, Result<String>>  convertToString(Function<T, String> func);

static <T> Function<T, Result<Boolean>> convertToBoolean();
static <T> Function<T, Result<Boolean>> convertToBoolean(Function<T, Boolean> func);

static <T> Function<T, Result<Integer>> convertToInteger();
static <T> Function<T, Result<Integer>> convertToInteger(Function<T, Integer> func);

static <T> Function<T, Result<Double>>  convertToDouble();
static <T> Function<T, Result<Double>>  convertToDouble(Function<T, Double> func);

Each conversion returns a Result so exceptions during the conversion become a Failure:

Function<String, Result<Integer>> toInt = Converting.convertToInteger(Integer::parseInt);

toInt.apply("42").ifPresentOrElse(
    System.out::println,                       // 42
    err -> System.err.println("nope: " + err)
);

The no-arg overloads pick a default converter for that target type.

SystemProperties

Read system properties safely — every method returns a Result, so unset or malformed values surface as Failure instead of null/NumberFormatException.

static Function<String, Result<String>>  systemProperty(Class qualifier);
static Function<String, Result<String>>  systemProperty(Class qualifier, String defaultValue);
static Function<String, Result<Boolean>> systemPropertyBoolean(Class qualifier);
static Function<String, Result<Boolean>> systemPropertyBoolean(Class qualifier, String defaultValue);
static Function<String, Result<Integer>> systemPropertyInt(Class qualifier);
static Function<String, Result<Integer>> systemPropertyInt(Class qualifier, String defaultValue);
static Function<String, Result<Double>>  systemPropertyDouble(Class qualifier);
static Function<String, Result<Double>>  systemPropertyDouble(Class qualifier, String defaultValue);

static BiFunction<Class, String, String>  qualifiedParameter();
static BiFunction<Class, String, Boolean> hasSystemProperty();
static Function<String, Boolean>          hasSystemProperty(Class qualifier);

The Class qualifier is prepended to the property name to namespace your config — e.g. for class com.acme.Db and key "port", the actual property looked up is com.acme.Db.port. This makes it harder for two unrelated modules to fight over the same global key.

class Db {}

int port = SystemProperties.systemPropertyInt(Db.class)
                           .apply("port")               // looks up com.example.Db.port
                           .getOrElse(() -> 5432);

StringFunctions

A large library (~86 public methods) of curried string operations — many ported from Strman-Java. Selected highlights:

// Basic
Function<String, String>          collapseWhitespace();
Function<String, String>          base64Encode();
Function<String, String>          base64Decode();
Predicate<String>                 notEmpty();

// Searching
BiFunction<String, String, Boolean>            contains();
BiFunction<String, String, Boolean>            endsWith();
BiFunction<String, String, Boolean>            notStartsWith();
BiFunction<String, String[], Boolean>          containsAll();
BiFunction<String, String[], Boolean>          containsAny();
BiFunction<String, String, Long>               countSubStr();

// Building
BiFunction<String, String, String>             append();
BiFunction<String, Integer, String>            repeat();
TriFunction<String, String, Integer, String>   leftPad();
BiFunction<String, String[], String>           appendArray();
BiFunction<String, Collection<String>, String> appendCollection();

// Indexing
BiFunction<String, Integer, Result<String>>    at();   // bounds-safe

The full method list lives in the source.

  • Result<T> — what every Converting / SystemProperties call hands back.
  • Transformations — composition helpers that go well with these.
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