Validify - Java validation library

The main purpose of this library is to provide a simple way to create more complicated validations and to accurately return information about errors that occurred during the validation. The secondary goal is to not use any external dependencies.

Available validations

At this moment some factory classes provides few out-of-the box self-explanatory (I hope so) validations.

CoreValidations
  - lengthIsEqual
  - lengthInRange
  - matches
  - allCharactersAreDigits
  - isEmpty
  - isNotEmpty
  - is
  - isIn
  - startsWith
  - endsWith
IntegerValidations
  - valueInRange

Custom validation

Creating custom validations is as simple as implementing io.github.emlagowski.validify.Validation functional interface. It have to return ValidationResult and to do that methods ValidationsResult.valid() and ValidationResult invalid(String message, Object... args) can be used.

Example of providing custom validation with implementing Validation interface.

public class IntegerValueInRangeValidation implements Validation<Integer> {

    private final Integer min;
    private final Integer max;

    public IntegerValueInRangeValidation(Integer min, Integer max) {
        this.min = min;
        this.max = max;
    }

    @Override
    public ValidationResult apply(Integer value) {
        return Optional.ofNullable(value)
                .filter(v -> min <= v && v <= max)
                .map(v -> ValidationResult.valid())
                .orElseGet(() -> ValidationResult.invalid("Value '%s' should be in the range [%d, %d]", value, min, max));
    }
}

Or it can be even shorter if you would use lambda expression like

public static Validation<Integer> valueInRange(int min, int max) {
    return value -> Optional.ofNullable(value)
            .filter(v -> min <= v && v <= max)
            .map(v -> ValidationResult.valid())
            .orElseGet(() -> ValidationResult.invalid("Value '%s' should be in the range [%d, %d]", value, min, max));
}

Validation API

On all Validations you can use and and or methods to combine them into one Validation.

Usage example

Example below shows how to achieve validation that checks if (value is 1-2 length string with only digits characters) or (value is predefined 'N/A' value) or (value is one of other predefined allowed values).

File: io.github.emlagowski.validify.CoreValidationsExample

List<String> allowedValues = Arrays.asList("A", "B", "C");
String allowedValue = "N/A";

Validation<String> validation = allCharactersAreDigits().and(lengthInRange(1, 2))
        .or(is(allowedValue))
        .or(isIn(allowedValues));

ValidationResult validationResult = validation.apply("value that not apply");

validationResult.getMessages().forEach(validationMessage -> System.out.println(validationMessage.getMessage()));

Result of above is

Not all character are digits in 'value that not apply'
Length of 'value that not apply' not in range [1, 2]
'value that not apply' is not 'N/A'
'value that not apply' is not in [A, B, C]

More examples

For more examples please see examples module or tests inside the validify-core module.