傑克遜檢查可選字段

Question

題

我正在 JAX-RS 項目中制作一個 POJO（人）並使用 Jackson。
我想創建一個可選的 String 字段（如該人居住的國家/地區）並能夠檢查其長度。

我的測試

通過參考這篇文章（ 如何使用 Jackson 定義可選的 json 字段），我知道如何創建一個可選字段。 但是如果我想用javax.validation.constraints.Pattern檢查它的長度，如下所示：

@Pattern(regexp = "(?:.{0,12})?")
private final String country;

國家不能為 NULL 或不再存在。

我嘗試添加@Optional ( org.jvnet.hk2.annotations.Optional ) 並指定國家，如private final Optional<String> country; . 這兩種方法我都沒有成功。

我的實際 POJO

import com.fasterxml.jackson.annotation.*;
import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import org.hibernate.validator.constraints.NotBlank;

import javax.validation.constraints.Pattern;

@JsonAutoDetect(creatorVisibility = Visibility.ANY, fieldVisibility = Visibility.ANY)
@JsonPropertyOrder({Person.LAST_NAME, Person.FIRST_NAME, Person.COUNTRY})
@JsonIgnoreProperties(ignoreUnknown = true)
public class Person {

    /**
     * The format string for the toString method
     */
    private static final String TO_STRING_FORMAT = "%S %s %s";

    /**
     * JSON property name for the last name
     */
    static final String LAST_NAME = "lastName";

    /**
     * JSON property name for the first name
     */
    static final String FIRST_NAME = "firstName";

    /**
     * JSON property name for the country
     */
    static final String COUNTRY = "country";

    /**
     * The last name of the person
     */
    @NotBlank
    private final String lastName;

    /**
     * The first name of the person
     */
    @NotBlank
    private final String firstName;

    /**
     * The country of the person
     */
    @Pattern(regexp = "(?:.{0,12})?")
    private final String country;

    /**
     * Returns an new {@code Person} with its properties initialized from parameters.
     *
     * @param lastName the last name of the person ({@link #lastName})
     * @param firstName the first name of the person ({@link #firstName})
     * @param country the country where the person live ({@link #country})
     */
    // Only used by Jackson for the JSON data deserialization
    @SuppressWarnings("unused")
    @JsonCreator
    private Person(@JsonProperty(Person.LAST_NAME) String lastName, @JsonProperty(Person.FIRST_NAME) String firstName, @JsonProperty(Person.COUNTRY) String country) {
        this.lastName = lastName.trim();
        this.firstName = firstName.trim();
        this.country = country.trim();
    }

    /**
     * Returns a new {@code Person} with its properties initialized from another one.
     *
     * @param person the instance used to create the new one
     */
    Person(Person person) {
        this.lastName = person.lastName;
        this.firstName = person.firstName;
        this.country = person.country;
    }

    /**
     * Returns a textual representation of the {@code Person}: {@link #lastName} {@link #firstName} {@link #country}.
     * <p>
     * The {@code lastName} is converted to uppercase for better readability of the person's name.
     *
     * @return a string representation of the {@code Person}
     */
    @Override
    public String toString() {
        return String.format(Person.TO_STRING_FORMAT, this.lastName, this.firstName, this.country);
    }
}

Answer 1

問題

問題是我在國家（可能是 NULL 值）上做了一個trim() ) 。 見下文：

@SuppressWarnings("unused")
@JsonCreator
private Person(@JsonProperty(Person.LAST_NAME) String lastName, @JsonProperty(Person.FIRST_NAME) String firstName, @JsonProperty(Person.COUNTRY) String country) {
    this.lastName = lastName.trim();
    this.firstName = firstName.trim();
    this.country = country.trim();
}

解決方案

我要感謝@TheOddCoder 的解決方案。 我的@Pattern正則表達式沒有改變，但構造函數private Person(...) (@JsonCreator)改變了以下內容：

@SuppressWarnings("unused")
@JsonCreator
private Person(@JsonProperty(Person.LAST_NAME) String lastName, @JsonProperty(Person.FIRST_NAME) String firstName, @JsonProperty(Person.COUNTRY) String country) {
    this.lastName = lastName.trim();
    this.firstName = firstName.trim();
    if(country == null) {
        this.country = country;
    } else {
        this.country = country.trim();
    }
}

Answer 2

在您的情況下，我可能會建議您不要為您的字段使用可選項，而是驗證您的國家/地區是否已設置並以這種方式處理。

private Person(@JsonProperty(Person.LAST_NAME) String lastName, @JsonProperty(Person.FIRST_NAME) String firstName, @JsonProperty(Person.COUNTRY) String country) {
    this.lastName = lastName.trim();
    this.firstName = firstName.trim();
    if(country == null) { //here you could also use the string empty or null check of apache or guava
        this.country = country;
    } else {
        this.country = country.trim();
    }
}

有了它，你就不必關心它是否設置了，不管怎樣，正則表達式都會匹配。

我希望這有幫助。