Jackson用Java 8反序列化elasticsearch作为LocalDateTime

Question

我们在elasticsearch索引中有一个用long填充的日期字段。

实地测绘是：

@Field(type = FieldType.Date)
@JsonFormat(shape = JsonFormat.Shape.NUMBER_INT)
private LocalDateTime created;

我在这个配置中使用Jackson JavaTimeModule和Jdk8Module：

@Bean
public ElasticsearchOperations elasticsearchTemplate() {
   return new ElasticsearchRestTemplate(client(), new CustomEntityMapper());
}

public static class CustomEntityMapper implements EntityMapper {

        private final ObjectMapper objectMapper;

        public CustomEntityMapper() {
            //we use this so that Elasticsearch understands LocalDate and LocalDateTime objects
            objectMapper = new ObjectMapper()
                              .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
                              .configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true)
                              .configure(DeserializationFeature.READ_DATE_TIMESTAMPS_AS_NANOSECONDS, false)
                              .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
                              .configure(SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS, false)
                              //MUST be registered BEFORE calling findAndRegisterModules
                              .registerModule(new JavaTimeModule())
                              .registerModule(new Jdk8Module());
            //only autodetect fields and ignore getters and setters for nonexistent fields when serializing/deserializing
            objectMapper.setVisibility(objectMapper.getSerializationConfig().getDefaultVisibilityChecker()
                            .withFieldVisibility(JsonAutoDetect.Visibility.ANY)
                            .withGetterVisibility(JsonAutoDetect.Visibility.NONE)
                            .withSetterVisibility(JsonAutoDetect.Visibility.NONE)
                            .withCreatorVisibility(JsonAutoDetect.Visibility.NONE));
            //load the other available modules as well
            objectMapper.findAndRegisterModules();
        }

        @Override
        public String mapToString(Object object) throws IOException {
            return objectMapper.writeValueAsString(object);
        }

        @Override
        public <T> T mapToObject(String source, Class<T> clazz) throws IOException {
            return objectMapper.readValue(source, clazz);
        }
}

但是，当我尝试使用字段解析索引中的实体时，例如：

"created" : 1563448935000

我收到一个错误：

com.fasterxml.jackson.databind.exc.MismatchedInputException: Unexpected token (VALUE_NUMBER_INT), expected VALUE_STRING: Expected array or string.

我认为，将long反序列化到约会是可能的，但我不知道我错过了什么。

如果我将它映射到Long，当然，如果该值存储为String，并且我们在@JsonFormat中对其进行了适当的格式化和格式化，那么它就会正常工作。但是也有可能拥有long->LocalDateTime吗？

Answer 1

要从LocalDateTime的时代起毫秒内构建1970-01-01T00:00:00Z，我们需要一个时区。在版本2.9.9中，当出现毫秒时，它将引发异常：

java.time.LocalDateTime不允许使用原始时间戳(1563448935000)：需要附加信息，如偏移量或时区(请参阅类Javadocs)

但是我们可以实现反序列化器，它将尝试使用默认时区来实现这一点。示例实现如下所示：

class MillisOrLocalDateTimeDeserializer extends LocalDateTimeDeserializer {

    public MillisOrLocalDateTimeDeserializer() {
        super(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
    }

    @Override
    public LocalDateTime deserialize(JsonParser parser, DeserializationContext context) throws IOException {
        if (parser.hasToken(JsonToken.VALUE_NUMBER_INT)) {
            long value = parser.getValueAsLong();
            Instant instant = Instant.ofEpochMilli(value);

            return LocalDateTime.ofInstant(instant, ZoneOffset.UTC);
        }

        return super.deserialize(parser, context);
    }

}

使用ZoneOffset.UTC。在您的情况下，您可以提供您的或使用系统默认。示例用法：

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import com.fasterxml.jackson.datatype.jsr310.deser.LocalDateTimeDeserializer;

import java.io.IOException;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        JavaTimeModule javaTimeModule = new JavaTimeModule();
        // override default
        javaTimeModule.addDeserializer(LocalDateTime.class, new MillisOrLocalDateTimeDeserializer());

        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(javaTimeModule);

        String json = "{\"created\":1563448935000}";
        System.out.println(mapper.readValue(json, Created.class));

    }
}

class Created {

    private LocalDateTime created;

    // getters, setters, toString
}

以上代码打印：

Created{created=2019-07-18T11:22:15}

编辑:使用Jackson 2.9.0，由于这问题，提供的代码将不会被调用，因为在注册定制模块之后调用的findAndRegisterModules将覆盖它。删除该调用将使整个场景工作。如果以上不适用于您的版本，则需要调试默认实现并找到原因。

Answer 2

使用Instant作为日期的杰克逊字段类型。这就简化了一切！您只需要注册模块：https://github.com/FasterXML/jackson-modules-java8