英文:
Check if null attribute present in Optional and return String Java Stream API
问题
我有以下内容：
class Personprivate String firstName;private String familyName;// 设置器和获取器
我有以下方法：
public String getFullName(Optional<Person> persons) {return persons.map(person -> (person.getFirstName() + " " + person.getFamilyName())).orElse("无效");}
我只想检查名字或姓氏是否为null，如果是，则显示“无效”该人。我在考虑添加一个验证方法，但我确定有一种更简单的方法，我想不出来。
英文:
I have the following
class Personprivate String firstName;private String familyName;// Setters and Getters
And I have the following method
public String getFullName(Optional<Person> persons) {return persons.map(person -> (person.getFirstName() + " " + person.getFamilyName())).orElse("Invalid");}
I just want to check if either first or last name is null, display "Invalid" for that person. I was thinking to add a method for validation but I am sure there is an easier way I cannot think about.
答案1
得分: 4
你正在查看 [Optional::filter][1]，在 map 之前：
return persons.filter(person -> person.getFamilyName() != null && person.getFirstName() != null).map(person -> person.getFirstName() + " " + person.getFamilyName()).orElse("无效");这意味着，如果姓氏和名字不为 null，则创建连接；否则返回“无效”消息，或者您甚至可以使用 `orElseThrow` 抛出异常。[1]: https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html#filter-java.util.function.Predicate-
英文:
You are looking to [Optional::filter][1], before the map:
return persons.filter(person -> person.getFamilyName() != null && person.getFirstName() != null).map(person -> person.getFirstName() + " " + person.getFamilyName()).orElse("Invalid");
Which mean, if the family and first names are not null then create your concatination, otherwise return an Invalid message, or you can even throw an exception by using orElseThrow
[1]: https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html#filter-java.util.function.Predicate-
答案2
得分: 1
你可以使用filter来实现：
public String getFullName(Optional<Person> persons) {return persons.filter(person -> Objects.nonNull(person.getFirstName()) && Objects.nonNull(person.getFamilyName())).map(person -> (person.getFirstName() + " " + person.getFamilyName())).orElse("Invalid");}
英文:
You can use filter for that:
public String getFullName(Optional<Person> persons) {return persons.filter(person -> Objects.nonNull(person.getFirstName()) && Objects.nonNull(person.getFamilyName())).map(person -> (person.getFirstName() + " " + person.getFamilyName())).orElse("Invalid");}
答案3
得分: 1
另一种函数式方法。
首先，为了进行必填字段验证，创建一个谓词构建器方法：
public static <T, F> Predicate<T> hasRequiredValue(Function<T, F> fieldGetter) {return fieldGetter.andThen(Objects::nonNull)::apply;}
然后稍微修改 getFullName 方法：
public Optional<String> getFullName(Person person) {return Optional.ofNullable(person).filter(hasRequiredValue(Person::getFamilyName)).filter(hasRequiredValue(Person::getFirstName)).map(p -> p.getFirstName() + " " + p.getFamilyName());}
然后按以下方式使用：
Person person = ...String fullName = getFullName(person).orElse("Invalid");
英文:
Another functional approach.
First create a predicate builder method for required field validation:
public static <T, F> Predicate<T> hasRequiredValue(Function<T, F> fieldGetter) {return fieldGetter.andThen(Objects::nonNull)::apply;}
And modify the getFullName a little bit:
public Optional<String> getFullName(Person person) {return Optional.ofNullable(person).filter(hasRequiredValue(Person::getFamilyName)).filter(hasRequiredValue(Person::getFirstName)).map(p -> p.getFirstName() + " " + p.getFamilyName());}
Then use it as follows:
Person person = ...String fullName = getFullName(person).orElse("Invalid");
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