SpringCloud - Jackson序列化LocalDateTime

夹胡碰

发布于 2021-06-17 19:51:32

2.7K0

发布于 2021-06-17 19:51:32

SpringCloud开发中，Jackson作为默认的序列化器，在跨服务调用过程中，序列化LocalDateTime时常发生格式不一致问题，下面将对SpringCloud中Jackson的序列化方式及源码进行分析。

专题参考:

Jackson - LocalDateTime序列化探索

1. 配置

maven

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.2.9.RELEASE</version>
</parent>
<properties>
    <spring-cloud.version>Hoxton.SR3</spring-cloud.version>
</properties>

2.反序列化

Controller

@PostMapping("/test")
public SpuDetailDTO test(@RequestBody SpuDetailDTO spuDetailDTO) throws JsonProcessingException {
    System.out.println(spuDetailDTO);
    return spuDetailDTO;
}

@Data
public class SpuDetailDTO {
    private LocalDateTime updateTime;
}

Post请求Body 以下两种格式都支持

{"updateTime": "2020-10-10T10:10:10"}

{"updateTime": [2014, 10, 10, 10, 10, 10]}

Result Json 返回格式默认为yyyy-MM-ddTHH:mm:ss

{"updateTime": "2020-10-10T10:10:10"}

3. 流程分析

在Spring启动的时候，会初始化Jackson的ObjectMapper，然后初始化JavaTimeModule，在JavaTimeModule中会默认加载LocalDateTime的序列化器(LocalDateTimeSerializer)和反序列化器(LocalDateTimeDeserializer)，最终将JavaTimeModule注册到ObjectMapper中。

LocalDateTimeDeserializer 反序列化支持yyyy-MM-ddTHH:mm:ss和yyyy-MM-ddTHH:mm:ss的格式。
LocalDateTimeSerializer 序列化默认使用yyyy-MM-ddTHH:mm:ss格式。

流程如下:

至此之后，所有的Controller接口的调用，或者Feign调用LocalDateTime的序列化和反序列化，都会使用该配置。

5. 源码分析

MappingJackson2HttpMessageConverter.MappingJackson2HttpMessageConverter()

public class MappingJackson2HttpMessageConverter extends AbstractJackson2HttpMessageConverter {

    ...
    public MappingJackson2HttpMessageConverter() {
        // TODO: 初始化
        this(Jackson2ObjectMapperBuilder.json().build());
    }

Jackson2ObjectMapperBuilder.build()

public class Jackson2ObjectMapperBuilder {
    ....
    public <T extends ObjectMapper> T build() {
        ObjectMapper mapper;
        // TODO: 初始化ObjectMapper
        if (this.createXmlMapper) {
            mapper = (this.defaultUseWrapper != null ?
                    new XmlObjectMapperInitializer().create(this.defaultUseWrapper, this.factory) :
                    new XmlObjectMapperInitializer().create(this.factory));
        }
        else {
            mapper = (this.factory != null ? new ObjectMapper(this.factory) : new ObjectMapper());
        }
        // TODO: 配置mapper
        configure(mapper);
        return (T) mapper;
    }

Jackson2ObjectMapperBuilder.configure()

public class Jackson2ObjectMapperBuilder {
    public void configure(ObjectMapper objectMapper) {
        Assert.notNull(objectMapper, "ObjectMapper must not be null");

        MultiValueMap<Object, Module> modulesToRegister = new LinkedMultiValueMap<>();
        if (this.findModulesViaServiceLoader) {
            ObjectMapper.findModules(this.moduleClassLoader).forEach(module -> registerModule(module, modulesToRegister));
        }
        else if (this.findWellKnownModules) {
            // TODO: 注册 Module
            registerWellKnownModulesIfAvailable(modulesToRegister);
        }

public class Jackson2ObjectMapperBuilder {
...
private void registerWellKnownModulesIfAvailable(MultiValueMap<Object, Module> modulesToRegister) {
    
    // jackson-datatype-jdk8
    ...

    try {
        Class<? extends Module> javaTimeModuleClass = (Class<? extends Module>)
                ClassUtils.forName("com.fasterxml.jackson.datatype.jsr310.JavaTimeModule", this.moduleClassLoader);
        // TODO: 默认加载jsr310的JavaTimeModule
        Module javaTimeModule = BeanUtils.instantiateClass(javaTimeModuleClass);
        modulesToRegister.set(javaTimeModule.getTypeId(), javaTimeModule);
    }
    catch (ClassNotFoundException ex) {
        // jackson-datatype-jsr310 not available
    }

    // Joda-Time present?
    ...
    // Kotlin present?
    ...
    }
}

JavaTimeModule无参构造函数

public final class JavaTimeModule extends SimpleModule
{
    ...
    public JavaTimeModule()
    {
        ...
        // TODO: 反序列化
        addDeserializer(LocalDateTime.class, LocalDateTimeDeserializer.INSTANCE);
        addDeserializer(LocalDate.class, LocalDateDeserializer.INSTANCE);
        addDeserializer(LocalTime.class, LocalTimeDeserializer.INSTANCE);
        ...
        // TODO: 序列化
        addSerializer(LocalDateTime.class, LocalDateTimeSerializer.INSTANCE);
        addSerializer(LocalDate.class, LocalDateSerializer.INSTANCE);
        addSerializer(LocalTime.class, LocalTimeSerializer.INSTANCE);
        ...
    }

LocalDateDeserializer.INSTANCE支持yyyy-MM-ddTHH:mm:ss和[yyyy, MM, dd, HH, mm, ss]格式的反序列化。 LocalDateTimeSerializer.INSTANCE也支持yyyy-MM-ddTHH:mm:ss和[yyyy, MM, dd, HH, mm, ss]的序列化。但是在Spring中,JacksonAutoConfiguration将SerializationFeature默认加载的WRITE_DATES_AS_TIMESTAMPS和WRITE_DURATIONS_AS_TIMESTAMPS置为false，导致仅支持format格式的输出。源码如下:

JacksonAutoConfiguration - Jackson配置

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(ObjectMapper.class)
public class JacksonAutoConfiguration {

    private static final Map<?, Boolean> FEATURE_DEFAULTS;

    static {
        Map<Object, Boolean> featureDefaults = new HashMap<>();
        // TODO: 设置为false
    featureDefaults.put(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        // TODO: 设置为false
        featureDefaults.put(SerializationFeature.WRITE_DURATIONS_AS_TIMESTAMPS, false);
        FEATURE_DEFAULTS = Collections.unmodifiableMap(featureDefaults);
    }

SerializationFeature - 序列化器功能

public enum SerializationFeature implements ConfigFeature
{
    ...
    WRITE_DATES_AS_TIMESTAMPS(true), // TODO: 默认为true
    ...
    WRITE_DURATIONS_AS_TIMESTAMPS(true),// TODO: 默认为true
    ...

LocalDateTimeSerializer - LocalDateTime序列化

public class LocalDateTimeSerializer extends JSR310FormattedSerializerBase<LocalDateTime>
{
    @Override
    public void serialize(LocalDateTime value, JsonGenerator g, SerializerProvider provider)
        throws IOException
    {
        // TODO: 如果使用 WRITE_DATES_AS_TIMESTAMPS 特性，并且format为空， 
        // 则序列化为[yyyy, MM, dd, HH, mm, ss]
        if (useTimestamp(provider)) {
            g.writeStartArray();
            _serializeAsArrayContents(value, g, provider);
            g.writeEndArray();
        } else {
            DateTimeFormatter dtf = _formatter;
            if (dtf == null) {
                dtf = _defaultFormatter();
            }
            g.writeString(value.format(dtf));
        }
    }

    protected boolean useTimestamp(SerializerProvider provider) {
        if (_useTimestamp != null) {
            return _useTimestamp.booleanValue();
        }
        if (_shape != null) {
            if (_shape == Shape.STRING) {
                return false;
            }
            if (_shape == Shape.NUMBER_INT) {
                return true;
            }
        }
        // assume that explicit formatter definition implies use of textual format
        // TODO: 是否设置 WRITE_DATES_AS_TIMESTAMPS 并且format为空
        return (_formatter == null) && (provider != null)
                && provider.isEnabled(getTimestampsFeature());
    }

6. 结论

SpringCloud中对于LocalDateTime，Jackson默认使用jackson-datatype-jsr310的JavaTimeModule进行序列化和反序列化配置，JacksonAutoConfiguration对序列化格式进行了调整，不采用数组的形式进行序列化，而采用format的形式。最终通过 LocalDateTimeDeserializer的deserialize实现反序列化，默认支持yyyy-MM-ddTHH:mm:ss和[yyyy, MM, dd, HH, mm, ss]格式。 LocalDateTimeSerializer的serialize实现序列化，默认支持yyyy-MM-ddTHH:mm:ss格式。