如何使用Java 8 Lambda结合Map重构if语句校验代码

原代码通过重复的if判断校验字段非空，复用性差且冗余。用Map存储字段提取逻辑和对应标识，结合Lambda遍历校验，能大幅简化代码，后续新增字段仅需在Map中添加条目即可。

重构方案一：直接映射字段获取器与错误信息 #

适合需要自定义不同错误信息的场景：

private void validateUserFields(User user) {
    Map<Supplier<Object>, String> fieldValidations = Map.of(
        user::getName, "The user's name cannot be null",
        user::getLastName, "The user's lastName cannot be null",
        user::getDni, "The user's dni cannot be null",
        user::getVehicle, "The user's vehicle cannot be null"
    );

    fieldValidations.forEach((fieldSupplier, errorMsg) -> {
        if (fieldSupplier.get() == null) {
            throw new RuntimeException(errorMsg);
        }
    });
}

重构方案二：统一错误信息格式 #

如果错误信息格式固定，可进一步简化，避免重复编写字符串：

private void validateUserFields(User user) {
    Map<Function<User, Object>, String> fieldValidations = Map.of(
        User::getName, "name",
        User::getLastName, "lastName",
        User::getDni, "dni",
        User::getVehicle, "vehicle"
    );

    fieldValidations.forEach((fieldExtractor, fieldName) -> {
        if (fieldExtractor.apply(user) == null) {
            throw new RuntimeException(String.format("The user's %s cannot be null", fieldName));
        }
    });
}

兼容Java 8的写法 #

若项目基于Java 8，Map.of()不可用，改用HashMap初始化：

private void validateUserFields(User user) {
    Map<Function<User, Object>, String> fieldValidations = new HashMap<>();
    fieldValidations.put(User::getName, "name");
    fieldValidations.put(User::getLastName, "lastName");
    fieldValidations.put(User::getDni, "dni");
    fieldValidations.put(User::getVehicle, "vehicle");

    fieldValidations.forEach((fieldExtractor, fieldName) -> {
        if (fieldExtractor.apply(user) == null) {
            throw new RuntimeException(String.format("The user's %s cannot be null", fieldName));
        }
    });
}

内容的提问来源于stack exchange，提问作者MATEO VALENCIA MINOTA