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/*
* Copyright 2000-2014 Vaadin Ltd.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.vaadin.data;
import java.io.Serializable;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Predicate;
/**
* A functional interface for validating user input or other potentially invalid
* data. When a validator instance is applied to a value of the corresponding
* type, it returns a <i>result</i> signifying that the value either passed or
* failed the validation.
* <p>
* For instance, the following validator checks if a number is positive:
*
* <pre>
* Validator<Integer> v = num -> {
* if (num >= 0)
* return Result.ok(num);
* else
* return Result.error("number must be positive");
* };
* </pre>
*
* @author Vaadin Ltd.
*
* @param <T>
* the type of the value to validate
*
* @see Result
*/
@FunctionalInterface
public interface Validator<T> extends Function<T, Result<T>>, Serializable {
/**
* Returns a validator that chains this validator with the given function.
* Specifically, the function may be another validator. The resulting
* validator first applies this validator, and if the value passes, then the
* given validator.
* <p>
* For instance, the following chained validator checks if a number is
* between 0 and 10, inclusive:
*
* <pre>
* Validator<Integer> v = Validator.from(num -> num >= 0, "number must be >= 0")
* .chain(Validator.from(num -> num <= 10, "number must be <= 10"));
* </pre>
*
* @param next
* the validator to apply next, not null
* @return a chained validator
*
* @see #from(Predicate, String)
*/
public default Validator<T> chain(Function<T, Result<T>> next) {
Objects.requireNonNull(next, "next cannot be null");
return val -> apply(val).flatMap(next);
}
/**
* Validates the given value. Returns a {@code Result} instance representing
* the outcome of the validation.
*
* @param value
* the input value to validate
* @return the validation result
*/
@Override
public Result<T> apply(T value);
/**
* Returns a validator that passes any value.
*
* @param <T>
* the value type
* @return an always-passing validator
*/
public static <T> Validator<T> alwaysPass() {
return v -> Result.ok(v);
}
/**
* Builds a validator out of a conditional function and an error message. If
* the function returns true, the validator returns {@code Result.ok()}; if
* it returns false or throws an exception, {@code Result.error()} is
* returned with the given message.
* <p>
* For instance, the following validator checks if a number is between 0 and
* 10, inclusive:
*
* <pre>
* Validator<Integer> v = Validator.from(num -> num >= 0 && num <= 10,
* "number must be between 0 and 10");
* </pre>
*
* @param <T>
* the value type
* @param guard
* the function used to validate, not null
* @param errorMessage
* the message returned if validation fails, not null
* @return the new validator using the function
*/
public static <T> Validator<T> from(Predicate<T> guard,
String errorMessage) {
Objects.requireNonNull(guard, "guard cannot be null");
Objects.requireNonNull(errorMessage, "errorMessage cannot be null");
return value -> {
try {
if (guard.test(value)) {
return Result.ok(value);
} else {
return Result.error(errorMessage);
}
} catch (Exception e) {
return Result.error(errorMessage);
}
};
}
}
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