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

Question

我有一种方法来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"));
}

收件人类:

@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SpringBoot和H2。

所以我还有一个 RecipientRepository 接口(interface):

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

findById() 方法的定义:

Optional<T> findById(ID var1);

Answer 1

方法findById()已经返回 Optional<T> ，因此您不需要使用额外的 Optional.ofNullable() 来包装结果在这种情况下。

实际上，该行:

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

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

相反，你可以这样写:

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