Java 8 Optional.ofNullable.map 产生非静态方法引用错误

Question

我有一种方法可以验证电子邮件的收件人。

在我的代码中 .map(Recipient::getId) 产生错误：

Non static method cannot be reference from a static context.

private Long verifyRecipient(Long recipientId) throws NotFoundException {
    return Optional.ofNullable(recipientRepository.findById(recipientId))
            .map(Recipient::getId)
            .orElseThrow(()-> new NotFoundException("recipient with ID" + recipientId +
                    " was not found"));
}

Recipient class:

@Entity
public class Recipient {
    @Id
    @GeneratedValue
    private Long id;

    @NotBlank
    private String name;

    @NotBlank
    @Email
    @Column(unique = true)
    private String emailAddress;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmailAddress() {
        return emailAddress;
    }

    public void setEmailAddress(String emailAddress) {
        this.emailAddress = emailAddress;
    }
}

我在内存数据库中使用了SpringBoot和H2。

所以我也有一个RecipientRepository接口：

public interface RecipientRepository extends JpaRepository<Recipient, Long> {}

findById() 方法的定义：

Optional<T> findById(ID var1);

Answer 1

方法 findById() 已经 returns 一个 Optional<T>，所以在这种情况下你不需要用额外的 Optional.ofNullable() 包装结果。

实际上，行：

Optional.ofNullable(recipientRepository.findById(recipientId));

returnsOptional<Optional<Recipient>>，这是多余的。

相反，您可以只写：

private Long verifyRecipient(Long recipientId) throws NotFoundException {
    return recipientRepository.findById(recipientId)
        .map(Recipient::getId)
        .orElseThrow(() ->
            new NotFoundException("Recipient with ID " + recipientId + " was not found"));
}

Java 8 Optional.ofNullable.map 产生非静态方法引用错误

Java 8 Optional.ofNullable.map producing Non static method reference error

java

spring-boot

java-8

in-memory-database