Java 8 FP inspired validation

Project has demonstrable example how Java 8 functional interfaces can be used to implemenent business validation and test conditions.

How to?

Validation

Given an example validation

private OperationResult<String> verifyTime() {
    return OperationResult.of(timeValidator.validate(LocalDateTime.now()));
}

private OperationResult<String> verifyName() {
    return OperationResult.success("James");
}

It's possible to chain opeations using flatMap as follows

OperationResult<String> chain =
    new OperationResult<String>()
        .flatMap(this::verifyTime)
        .flatMap(this::verifyName)
        .onSuccess(() -> System.out.println("success"));


assertFalse(chain.hasError());

Please refer tests for more details.

Test conditions

Java 8 functional interfaces can be extended to build your owns. An example can be find below:

public interface TestCondition extends Supplier<Boolean> {

    static TestCondition isUuidNull(UUID uuid) {
        return () -> Objects.isNull(uuid);
    }

    static TestCondition hasText(String s) {
        return () -> s != null && !s.trim().isEmpty();
    }

    default TestCondition and(TestCondition other) {
        return () -> {
            final boolean isValid = this.get();
            return isValid ? other.get() : false;
        };
    }

    default boolean isTrue() {
        return this.get();
    }
}

Given this it's possible to compose functions as follows:

isUuidNull(uuid).and(hasText(s)).isTrue()

Please refer tests for more details.