当有 JsonSerializer<Timestamp>() 时，JsonSerializer<Date>() 不适用于 java.util.Date 字段

Question

在我的 java 应用程序中，我使用 JsonSerializer 和 JsonSerializer() 分别序列化 java.util.Date 和 java.sql.Timestamp 字段。但问题是，当我使用 gson 将对象解析为 json 字符串时 java. util.Date 字段使用 JsonSerializer() 序列化程序而不是 JsonSerializer。 下面是我的代码。

Gson gson;
GsonBuilder builder;
SimpleDateFormat dtf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
SimpleDateFormat dtfDate=new SimpleDateFormat("yyyy-MM-dd");
builder = new GsonBuilder();

builder.registerTypeAdapter(Timestamp.class, new JsonSerializer<Timestamp>() {
    @Override
    public JsonElement serialize(Timestamp src, Type typeOfSrc, JsonSerializationContext context) {
        dtf.setTimeZone(TimeZone.getTimeZone("UTC"));
        String jsDate = dtf.format(src);
        System.out.println("Timestamp : src - "+src+" jsDate - "+jsDate+" typeOfSrc - "+typeOfSrc);
        return new JsonPrimitive(jsDate);
    }
});
builder.registerTypeAdapter(Date.class, new JsonSerializer<Date>() {
    @Override
    public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext context) {
        String jsDate = dtfDate.format(src);
        System.out.println("Date : src - "+src+" jsDate - "+jsDate+" typeOfSrc - "+typeOfSrc);
        return new JsonPrimitive(jsDate);
    }
});
gson = builder.create();
PersonSubstitution  personSubstitution = loopDao.getPersonSubstitution(Integer.parseInt(deptId),date);
String jsonAccts = gson.toJson(personSubstitution, PersonSubstitution.class);

PersonSubstitution.class ：

import javax.persistence.*;
import java.io.Serializable;
import java.sql.Timestamp;
import java.util.Date;
import java.util.Objects;


@Entity
@Table(name = "person_substitution")
public class PersonSubstitution implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @JoinColumn(name = "dept_id", referencedColumnName = "id", nullable = false)
    @ManyToOne(optional = false)
    private Departments deptId;

    @Column(name = "date")
    private Date date;

    @JoinColumn(name = "staff_id", referencedColumnName = "person_id", nullable = false)
    @OneToOne(optional = false)
    private Person staffId;

    @Column(name = "created_on")
    private Timestamp createdOn;

    public PersonSubstitution() {

    }

    public PersonSubstitution(int id, Departments deptId, Date date, Person staffId, Timestamp createdOn) {
        this.id = id;
        this.deptId = deptId;
        this.date = date;
        this.staffId = staffId;
        this.createdOn = createdOn;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Departments getDeptId() {
        return deptId;
    }

    public void setDeptId(Departments deptId) {
        this.deptId = deptId;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public Person getStaffId() {
        return staffId;
    }

    public void setStaffId(Person staffId) {
        this.staffId = staffId;
    }

    public Timestamp getCreatedOn() {
        return createdOn;
    }

    public void setCreatedOn(Timestamp createdOn) {
        this.createdOn = createdOn;
    }
}

我将System.out.println() 放入两个序列化程序中，并且只有时间戳干的工作如下：

Timestamp : src - 2019-11-28 00:00:00.0 jsDate - 2019-11-27 18:30:00 typeOfSrc - class java.sql.Timestamp
Timestamp : src - 2019-11-25 12:08:14.0 jsDate - 2019-11-25 06:38:14 typeOfSrc - class java.sql.Timestamp

那么日期字段有什么方法可以使用builder.registerTypeAdapter(Date.class, new JsonSerializer<Date>() {...} 而不是builder.registerTypeAdapter(Date.class, new JsonSerializer<Timestamp>() {...} ??

Answer 1

它是这样工作的，因为在运行时 date 和 createdOn 是 Timestamp。您需要将给定的序列化程序分配给一个字段。因此，您需要创建一个自定义序列化程序：

class DateJsonSerializer implements JsonSerializer<Date> {

    private final ThreadLocal<SimpleDateFormat> formatter = ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyy-MM-dd"));

    @Override
    public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext context) {
        String formatted = formatter.get().format(src);

        return new JsonPrimitive(formatted);
    }
}

Timestamp序列化器：

class TimestampJsonSerializer implements JsonSerializer<Timestamp> {

    private final ThreadLocal<SimpleDateFormat> formatter = ThreadLocal.withInitial(() -> {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
        return dateFormat;
    });

    @Override
    public JsonElement serialize(Timestamp src, Type typeOfSrc, JsonSerializationContext context) {
        String formatted = formatter.get().format(src);
        return new JsonPrimitive(formatted);
    }
}

并为Date 字段声明它：

@JsonAdapter(DateJsonSerializer.class)
private Date date;

您仍然可以将其注册为 Date 类的全局序列化程序：

Gson gson = new GsonBuilder()
        .setPrettyPrinting()
        .registerTypeAdapter(Timestamp.class, new TimestampJsonSerializer())
        .registerTypeAdapter(Date.class, new DateJsonSerializer())
        .create();

注意：我使用ThreadLocal是因为SimpleDateFormat不是线程安全的。