如何将包含LocalDate字段的json转换为可反序列化格式？

Question

我有一个对象存储在字符串中，其中一个字段是LocalDate。

"from": {
        "year": 1000,
        "month": "JANUARY",
        "era": "CE",
        "dayOfMonth": 1,
        "dayOfWeek": "WEDNESDAY",
        "dayOfYear": 1,
        "leapYear": false,
        "monthValue": 1,
        "chronology": {
            "calendarType": "iso8601",
            "id": "ISO"
        }
    }

我该如何将这个JSON转换为可用于反序列化的格式？

以下是代码：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;


ObjectMapper om = new ObjectMapper();
om.registerModule(new JavaTimeModule());
MyCustomObject obj = om.readValue(json, MyCustomObject.class); //error

导致这个异常的原因:

com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (START_OBJECT), expected VALUE_STRING: Expected array or string.

这是我使用的MyCustomObject类，它与LocalDate相关：

MyCustomObject<LocalDate>

public class MyCustomObject<T> {
    private T from;
    private T to;

    public MyCustomObject() {
    }

    public T getFrom() {
        return this.from;
    }

    public void setFrom(T from) {
        this.from = from;
    }

    public T getTo() {
        return this.to;
    }

    public void setTo(T to) {
        this.to = to;
    }
}

- naglas

---

你能分享一下你的 MyCustomObject 代码吗？ - cнŝdk

Answer 1

将您的 MyCustomObject.class 替换为以下内容：

==================================
package ;
public class Chronology
{
    private String calendarType;

    private String id;

    public void setCalendarType(String calendarType){
        this.calendarType = calendarType;
    }
    public String getCalendarType(){
        return this.calendarType;
    }
    public void setId(String id){
        this.id = id;
    }
    public String getId(){
        return this.id;
    }
}

==================================
package ;
public class From
{
    private int year;

    private String month;

    private String era;

    private int dayOfMonth;

    private String dayOfWeek;

    private int dayOfYear;

    private boolean leapYear;

    private int monthValue;

    private Chronology chronology;

    public void setYear(int year){
        this.year = year;
    }
    public int getYear(){
        return this.year;
    }
    public void setMonth(String month){
        this.month = month;
    }
    public String getMonth(){
        return this.month;
    }
    public void setEra(String era){
        this.era = era;
    }
    public String getEra(){
        return this.era;
    }
    public void setDayOfMonth(int dayOfMonth){
        this.dayOfMonth = dayOfMonth;
    }
    public int getDayOfMonth(){
        return this.dayOfMonth;
    }
    public void setDayOfWeek(String dayOfWeek){
        this.dayOfWeek = dayOfWeek;
    }
    public String getDayOfWeek(){
        return this.dayOfWeek;
    }
    public void setDayOfYear(int dayOfYear){
        this.dayOfYear = dayOfYear;
    }
    public int getDayOfYear(){
        return this.dayOfYear;
    }
    public void setLeapYear(boolean leapYear){
        this.leapYear = leapYear;
    }
    public boolean getLeapYear(){
        return this.leapYear;
    }
    public void setMonthValue(int monthValue){
        this.monthValue = monthValue;
    }
    public int getMonthValue(){
        return this.monthValue;
    }
    public void setChronology(Chronology chronology){
        this.chronology = chronology;
    }
    public Chronology getChronology(){
        return this.chronology;
    }
}

==================================
package ;
public class MyCustomObject
{
    private From from;

    public void setFrom(From from){
        this.from = from;
    }
    public From getFrom(){
        return this.from;
    }
}

- Avinash Roy

Answer 2

LocalDate 在 JSON 中存储不正确。

解决问题的正确方法是确保生成 JSON 的 ObjectMapper 已经注册了 JavaTimeModule 或者 Jdk8Module。这样可以确保 LocalDate 被正确序列化为一个 [year, month, day] 的 JSON 数组。

一种暴力的方法是按照 @Roy 在另一个答案中提出的解决方案，手动将每个相关字段转换为 LocalDate。大致如下：

LocalDate date = LocalDate.now()
        .with(ChronoField.YEAR, year)
        .with(ChronoField.MONTH_OF_YEAR, Month.valueOf(month).getValue())
        .with(ChronoField.DAY_OF_MONTH, dayOfMonth);

这显然很容易出错，也不是类的预期使用方式。

- Henrik Aasted Sørensen