我在尝试反序列化以下类时遇到问题:
public class MetricValuesDto {
private Map<MetricType, MetricValueDto<?>> metricValues;
public MetricValuesDto() {
}
public MetricValuesDto(Map<MetricType, MetricValueDto<?>> metricValues) {
this.metricValues = metricValues;
}
public Map<MetricType, MetricValueDto<?>> getMetricValues() {
return metricValues;
}
public void setMetricValues(Map<MetricType, MetricValueDto<?>> metricValues) {
this.metricValues = metricValues;
}
}
我的通用抽象类:
public abstract class MetricValueDto<T> {
private T value;
private MetricTrend trend;
public MetricValueDto(T value, MetricTrend trend) {
this.value = value;
this.trend = trend;
}
public T getValue() {
return value;
}
public void setValue(T value) {
this.value = value;
}
public MetricTrend getTrend() {
return trend;
}
public void setTrend(MetricTrend trend) {
this.trend = trend;
}
}
我有两个实现MetricValueDto
的具体类:
IntMetricValueDto:
public class IntMetricValueDto extends MetricValueDto<Integer> {
public IntMetricValueDto(Integer value, MetricTrend trend) {
super(value, trend);
}
}
FloatMetricValueDto:
public class FloatMetricValueDto extends MetricValueDto<Float> {
public FloatMetricValueDto(Float value, MetricTrend trend) {
super(value, trend);
}
}
知道反MerialValueDto的正确策略是什么,所以我可以通过ObjectMapper或RestTemplate来解析它?每当我跑:
restTemplate.exchange("myEndpoint", HttpMethod.GET, entity, DataCollectionEventDto.class);
我得到了
引起:com.fasterxml.jackson.databind.JsonMappingException:无法构造com.resson.dto.MetricValueDto的实例:抽象类型需要映射到具体类型,具有自定义反序列化器或包含其他类型信息< / p>
DataCollectionEventDto:
public class DataCollectionEventDto {
private List<MapLayerDto> mapLayers;
@JsonUnwrapped
private MetricValuesDto metricValues;
public List<MapLayerDto> getMapLayers() {
return mapLayers;
}
public void setMapLayers(List<MapLayerDto> mapLayers) {
this.mapLayers = mapLayers;
}
public MetricValuesDto getMetricValues() {
return metricValues;
}
public void setMetricValues(MetricValuesDto metricValues) {
this.metricValues = metricValues;
}
@Override
public String toString() {
return ToStringBuilder.reflectionToString(this);
}
}
我基本上已经尝试过网络上的所有内容而无法使其发挥作用;任何建议都会有所帮助。
答案 0 :(得分:8)
将 JsonSubTypes 注释与 JsonTypeInfo 一起使用以指示子类型。 属性属性 JsonTypeInfo 用于区分不同的子类。
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "typ")
@JsonSubTypes({
@JsonSubTypes.Type(value = IntMetricValueDto.class, name = "INT"),
@JsonSubTypes.Type(value = FloatMetricValueDto.class, name = "FLT")}
public abstract class MetricValueDto<T> {
private T value;
private MetricTrend trend;
...
}
答案 1 :(得分:2)
虽然JsonTypeInfo
有效,但会在响应中添加特定于实现的详细信息,以后可能会对API客户端造成混淆。
我最终实现了自定义StdDeserializer:
public class MetricValueDtoDeserializer<T> extends StdDeserializer<MetricValueDto<T>> {
private static final long serialVersionUID = 1L;
public MetricValueDtoDeserializer() {
this(null);
}
public MetricValueDtoDeserializer(Class<?> vc) {
super(vc);
}
private ObjectMapper mapper;
@Override
public MetricValueDto<T> deserialize(JsonParser jsonParser, DeserializationContext context)
throws IOException, JsonProcessingException {
String metricType = jsonParser.getCurrentName();
mapper = (ObjectMapper) jsonParser.getCodec();
ObjectNode objectNode = (ObjectNode) mapper.readTree(jsonParser);
Iterator<Entry<String, JsonNode>> elementsIterator = objectNode.fields();
Number number = null;
while (elementsIterator.hasNext()) {
Entry<String, JsonNode> element = elementsIterator.next();
String key = element.getKey();
if (key.equals("value")) {
number = parseValue(element, metricType);
}
if (key.equals("trend")) {
MetricTrend metricTrend = parseTrend(element);
return (produceMetricValueDto(number, metricTrend));
}
}
throw new IOException();
}
@SuppressWarnings("unchecked")
private MetricValueDto<T> produceMetricValueDto(Number number, MetricTrend metricTrend) throws IOException {
if (number instanceof Integer) {
return (MetricValueDto<T>) new IntMetricValueDto((Integer) number, metricTrend);
} else if (number instanceof Float) {
return (MetricValueDto<T>) new FloatMetricValueDto((Float) number, metricTrend);
}
throw new IOException();
}
private MetricTrend parseTrend(Entry<String, JsonNode> element)
throws JsonProcessingException {
String trend = mapper.treeToValue(element.getValue(), String.class);
if (trend == null) {
return null;
} else {
return MetricTrend.valueOf(trend);
}
}
private Number parseValue(Entry<String, JsonNode> element, String metricType)
throws IOException {
if (metricType.equals(MetricType.CANOPY_COVERAGE.toValue())
|| metricType.equals(MetricType.PLANT_SIZE.toValue())) {
return mapper.treeToValue(element.getValue(), Float.class);
} else if (metricType.equals(MetricType.INSECT_COUNT.toValue())
|| metricType.equals(MetricType.PLANT_COUNT.toValue())) {
return mapper.treeToValue(element.getValue(), Integer.class);
}
throw new IOException();
}
}
代码最终比JsonTypeInfo
更复杂,但API客户端并不知道特定于实现的细节。