Jackson 将 Instant 序列化为纳秒问题

Question

Jackson串行化java.time.Instant与WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS默认启用。

它JSON是这样产生的

{ "timestamp":1421261297.356000000 }

我想知道是否有办法摆脱最后的零。我想要这样的东西：

{ "timestamp":1421261297.356 }

我试过：

mapper.configure( SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS, false );
mapper.configure( SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, true );

但是此配置将其更改为毫秒表示1421261297356。我想要秒部分和小数毫秒部分。

Answer 1

当我们使用Java 8 Time包时，Jackson好主意是使用jackson-modules-java8项目，该项目为许多准备使用的序列化器和反序列化器提供服务。要启用它，我们需要注册JavaTimeModule模块。使用Instant InstantSerializer进行序列化。当我们检查它是如何实现时，我们会发现在幕后使用了DecimalUtils.toDecimal方法。看起来总是在纳秒值的末尾添加零。

我们可以编写我们的InstantSerializerwhich 以所需的方式序列化它。因为这个项目中的类还没有准备好轻松扩展，我们需要实现许多不需要的方法和构造函数。我们还需要在我们的项目com.fasterxml.jackson.datatype.jsr310.ser包中创建并在那里创建我们的实现。见下面的例子：

package com.fasterxml.jackson.datatype.jsr310.ser;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;

import java.io.IOException;
import java.math.BigDecimal;
import java.time.Instant;
import java.time.format.DateTimeFormatter;
import java.util.function.ToIntFunction;
import java.util.function.ToLongFunction;

public class ShortInstantSerializer extends InstantSerializerBase<Instant> {

    private ToLongFunction<Instant> getEpochSeconds = Instant::getEpochSecond;
    private ToIntFunction<Instant> getNanoseconds = i -> i.getNano() / 1_000_000;

    public ShortInstantSerializer() {
        super(Instant.class, Instant::toEpochMilli, Instant::getEpochSecond, Instant::getNano, null);
    }

    protected ShortInstantSerializer(ShortInstantSerializer base, Boolean useTimestamp, Boolean useNanoseconds, DateTimeFormatter formatter) {
        super(base, useTimestamp, useNanoseconds, formatter);
    }

    @Override
    protected JSR310FormattedSerializerBase<?> withFormat(Boolean useTimestamp, DateTimeFormatter formatter, JsonFormat.Shape shape) {
        return new ShortInstantSerializer(this, useTimestamp, null, formatter);
    }

    @Override
    public void serialize(Instant value, JsonGenerator generator, SerializerProvider provider) throws IOException {
        if (useTimestamp(provider)) {
            if (useNanoseconds(provider)) {
                generator.writeNumber(new BigDecimal(toShortVersion(value)));
                return;
            }
        }

        super.serialize(value, generator, provider);
    }

    private String toShortVersion(final Instant value) {
        return getEpochSeconds.applyAsLong(value) + "." + padWithZeros(getNanoseconds.applyAsInt(value));
    }

    private String padWithZeros(final int value) {
        return String.format("%1$3s", String.valueOf(value)).replace(' ', '0');
    }
}

以及如何使用它的示例：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import com.fasterxml.jackson.datatype.jsr310.ser.ShortInstantSerializer;

import java.time.Instant;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        JavaTimeModule javaTimeModule = new JavaTimeModule();
        javaTimeModule.addSerializer(Instant.class, new ShortInstantSerializer());

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(javaTimeModule);
        mapper.disable(SerializationFeature.INDENT_OUTPUT);

        System.out.println(mapper.writeValueAsString(new Element()));
    }
}

class Element {

    private Instant timestamp = Instant.now();

    public Instant getTimestamp() {
        return timestamp;
    }

    public void setTimestamp(Instant timestamp) {
        this.timestamp = timestamp;
    }
}

上面的代码打印：

{"timestamp":1559074287.223}

如果您想在所有情况下都删除所有零，请编写您自己getNanoseconds在ShortInstantSerializer类中声明的函数。