Java 8 Optional.ofNullable.map 生成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：

不能从静态上下文引用非静态方法。

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：

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

findById()方法的定义：

Optional<T> findById(ID var1);

Answer 1

该方法findById()已经返回一个Optional<T>，因此在这种情况下，您不需要用额外的Optional.ofNullable()包装结果。

实际上，这行：

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

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

相反，你可以只写：

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