Jackson，将纯 JSON 数组反序列化为单个 Java 对象

Question

一项外部服务正在提供一个包含 plain/primitive 个元素的 JSON 数组（因此没有字段名称，也没有嵌套的 JSON 对象）。例如：

["Foo", "Bar", 30]

我想使用 Jackson 将其转换为以下 Java class 的实例：

class Person {
    private String firstName;
    private String lastName;
    private int age;

    Person(String firstName, String lastName, int age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }
}

（此 class 可根据需要进行调整。）

问题：是否可以使用类似的方式将此 JSON 反序列化为 Java？

Person p = new ObjectMapper().readValue(json, Person.class);

或者这是否只能通过为此人编写自定义 Jackson 反序列化器才能实现 class？

我确实尝试了以下方法，但没有用：

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class Person {
    private String firstName;
    private String lastName;
    private int age;

    @JsonCreator
    public Person(
            @JsonProperty(index = 0) String firstName, 
            @JsonProperty(index = 1) String lastName, 
            @JsonProperty(index = 2) int age) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.age = age;
    }

    public static void main(String[] args) throws IOException {
        String json = "[\"Foo\", \"Bar\", 30]";
        Person person = new ObjectMapper().readValue(json, Person.class);
        System.out.println(person);
    }
}

结果：Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Argument #0 of constructor [constructor for Person, annotations: {interface com.fasterxml.jackson.annotation.JsonCreator=@com.fasterxml.jackson.annotation.JsonCreator(mode=DEFAULT)}] has no property name annotation; must have name when multiple-parameter constructor annotated as Creator at [Source: (String)"["Foo", "Bar", 30]"; line: 1, column: 1]

Answer 1

您不需要@JsonCreator，只需使用@JsonFormat(shape = JsonFormat.Shape.ARRAY)

@JsonFormat(shape = JsonFormat.Shape.ARRAY)
public static class Person {
    @JsonProperty
    private String firstName;
    @JsonProperty
    private String lastName;
    @JsonProperty
    private int age;
}

如果您需要在 bean 中保留一些替代字段声明顺序，请使用 @JsonPropertyOrder({"firstName", "lastName", "age" } )。

Jackson，将纯 JSON 数组反序列化为单个 Java 对象

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jackson2

jackson-databind