我如何使用杰克逊JSON映射与Java 8 LocalDateTime?

jsonmappingexception:不能实例化类型[简单类型,java.time类]的值。LocalDateTime] from JSON字符串;没有单字符串构造函数/工厂方法(通过引用链:MyDTO["field1"]->SubDTO["date"])


当前回答

        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-parameter-names</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jdk8</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-jsr310</artifactId>
        </dependency>

添加这些依赖项并启用这些模块。这应该会有帮助

    private static final ObjectMapper mapper = new ObjectMapper().findAndRegisterModules();

其他回答

在Jackson JSR的新版本中,例如,registerModule(new JSR310Module())已弃用,现在建议使用JavaTimeModule

import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JacksonFactory {
    private static ObjectMapper objectMapper = null;
    public static ObjectMapper getObjectMapper() {
        if (objectMapper == null) {
            objectMapper = new ObjectMapper();
            objectMapper.registerModule(new JavaTimeModule());
        }
        return objectMapper;
    }
}

我想为Spring的DurationStyle解析提供支持,在使用Jackson反序列化的自定义配置文件中的属性文件中提供支持,例如将20s序列化为Duration PT20S。我通过在ObjectMapper实例上注册一个自定义反序列化器来实现这一点:

@Bean("customConfigMapper")
public ObjectMapper customConfigMapper() {
    final ObjectMapper mapper = new ObjectMapper();
    final SimpleModule module = new SimpleModule();
    module.addDeserializer(Duration.class, new SpringDurationStyleDeserializer());
    mapper.registerModule(module);
    return mapper;
}

public static class SpringDurationStyleDeserializer extends JsonDeserializer<Duration> {
    @Override
    public Duration deserialize(JsonParser jsonParser, DeserializationContext __) throws IOException {
        return Optional.ofNullable(jsonParser.getText()).map(DurationStyle::detectAndParse).orElse(null);
    }
}

更新:由于历史原因,留下这个答案,但我不建议这样做。请参阅上面接受的答案。

告诉Jackson使用自定义的[反]序列化类进行映射:

@JsonSerialize(using = LocalDateTimeSerializer.class)
@JsonDeserialize(using = LocalDateTimeDeserializer.class)
private LocalDateTime ignoreUntil;

提供自定义类:

public class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {
    @Override
    public void serialize(LocalDateTime arg0, JsonGenerator arg1, SerializerProvider arg2) throws IOException {
        arg1.writeString(arg0.toString());
    }
}

public class LocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {
    @Override
    public LocalDateTime deserialize(JsonParser arg0, DeserializationContext arg1) throws IOException {
        return LocalDateTime.parse(arg0.getText());
    }
}

随机事实:如果我在类上面嵌套并且不使它们静态,错误消息是奇怪的: httpmediatypenotsupportedexception:内容类型'application/json;charset=UTF-8'不支持

如果你正在使用Jersey,那么你需要像其他人建议的那样添加Maven依赖项(jackson- dattype -jsr310),并像这样注册你的对象映射器实例:

@Provider
public class JacksonObjectMapper implements ContextResolver<ObjectMapper> {

  final ObjectMapper defaultObjectMapper;

  public JacksonObjectMapper() {
    defaultObjectMapper = createDefaultMapper();
  }

  @Override
  public ObjectMapper getContext(Class<?> type) {
    return defaultObjectMapper;
  }

  private static ObjectMapper createDefaultMapper() {
    final ObjectMapper mapper = new ObjectMapper();    
    mapper.registerModule(new JavaTimeModule());
    return mapper;
  }
}

当在你的资源中注册Jackson时,你需要像这样添加这个映射器:

final ResourceConfig rc = new ResourceConfig().packages("<your package>");
rc
  .register(JacksonObjectMapper.class)
  .register(JacksonJaxbJsonProvider.class);

不幸的是,这里提出的解决方案在我的环境中不起作用。 但说实话,使用java8时间对象作为dto毕竟不是一个很好的主意。

我建议创建自定义dto,不要依赖于不稳定的库,它可能在下次jdk发布后崩溃。这种方法也符合反腐败层和适配器模式的良好实践。

下面是DTO的示例:

public class ReportDTO implements Serializable {

    private YearMonthDTO yearMonth;

    public YearMonthDTO getYearMonth() {
        return yearMonth;
    }

    public void setYearMonth(final YearMonthDTO yearMonth) {
        this.yearMonth = yearMonth;
    }

    public void fromYearMonth(final YearMonth yearMonth) {
        this.yearMonth = new YearMonthDTO(yearMonth.getYear(), 
                              yearMonth.getMonthValue());
    }

}

public static class YearMonthDTO {

    private int year;

    private int monthValue;

    public YearMonthDTO() {

    }

    public YearMonthDTO(int year, int monthValue) {
        this.year = year;
        this.monthValue = monthValue;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getMonthValue() {
        return monthValue;
    }

    public void setMonthValue(int monthValue) {
        this.monthValue = monthValue;
    }

}

当然,这取决于你的情况,以及你要用这个解决方案做的工作量。与任何模式一样,此解决方案并不适用于所有情况。

无论如何,目前最好的答案似乎不再适用了。我没有尝试其他解决方案,但我决定在这个简单的案例中不依赖任何库。