Jackson 使用 Java 8 将 elasticsearch 反序列化为 LocalDateTime

Question

我们有一个用long弹性搜索索引填充的日期字段。

字段映射为：

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

我使用Jackson JavaTimeModule和Jdk8Module使用此配置：

@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);
        }
}

但是当我尝试使用以下字段解析索引中的实体时：

"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，可以将 a 反序列化为long日期，但我看不出我遗漏了什么。

如果我将它映射到Long它当然可以工作，并且如果值存储为String并且我们在@JsonFormat. 但也有可能long->LocalDateTime吗？

Answer 1

要从我们需要一个时区LocalDateTime的纪元几毫秒开始构建1970-01-01T00:00:00Z。在2.9.9版本中，出现毫秒时抛出异常：

原始时间戳 (1563448935000) 不允许用于 java.time.LocalDateTime：需要附加信息，例如偏移量或时区（请参阅 Javadocs 类）

但是我们可以实现我们的反序列化器，它会尝试使用默认时区执行此操作。示例实现可能如下所示：

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);
    }

}

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

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
}

上面的代码打印：

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

编辑：使用Jackson 2.9.0，由于这个问题，提供的代码将不会被调用，因为findAndRegisterModules在注册自定义模块后调用将覆盖它。删除该调用将使整个场景工作。如果以上对您的版本不起作用，您需要调试默认实现并找到原因。