所以我的 JSON 看起来像这样:
{
"ActivityDisplayModel" : {
"name" : "lunch with friends",
"startTime" : "12:00:00",
"type" : {
"id" : "MEAL",
"description" : "Meal"
},
"complete" : false
}
}
我正在尝试找到让 @JsonTypeInfo
不再因为在 type
对象中包含类型参数而生我的气。当字段 type
是一个 String 而不是一个对象本身时,我已经开始工作了,但是为了以后的处理,我需要它作为一个对象。我知道以下内容不起作用,我猜有一种方法可以使用 JsonTypeInfo.Id.CUSTOM ,但是在互联网上翻遍之后,没有出现 JSON 的完整示例。另外,如果 objectMapper 设置可以做到这一点,我会洗耳恭听。
/**
* My ActivityDisplayModel Abstract Class
*/
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type.id")
@JsonSubTypes({
@JsonSubTypes.Type(value = MealDisplayModel.class, name = "MEAL"),
@JsonSubTypes.Type(value = EntertainmentDisplayModel.class, name = "ENTERTAINMENT")
})
public abstract class ActivityDisplayModel {
...
以上基本上是我想做的,但当然我得到一个异常(exception):
Could not read JSON: Could not resolve type id '{' into a subtype of [simple type, class ... .ActivityDisplayModel]
这么简单的问题,只看JSON更深一层,谁能想到会这么麻烦?
最佳答案
我知道从最初的问题到现在已经 3 年了,但是点嵌套属性仍然不受支持,也许这会对某人有所帮助。我最终创建了一个 NestedTypeResolver
类,因此我们可以按预期使用点语法。只需将 @JsonTypeResolver(NestedTypeResolver.class)
添加到任何具有嵌套鉴别器的类中,发布者的原始尝试就会起作用:
/**
* My ActivityDisplayModel Abstract Class
*/
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type.id")
@JsonSubTypes({
@JsonSubTypes.Type(value = MealDisplayModel.class, name = "MEAL"),
@JsonSubTypes.Type(value = EntertainmentDisplayModel.class, name = "ENTERTAINMENT")
})
@JsonTypeResolver(NestedTypeResolver.class)
public abstract class ActivityDisplayModel {
嵌套类型解析器:
/**
* Allows using nested "dot" dyntax for type discriminators. To use, annotate class with @JsonTypeResolver(NestedTypeResolver.class)
*/
public class NestedTypeResolver extends StdTypeResolverBuilder {
@Override
public TypeDeserializer buildTypeDeserializer(DeserializationConfig config, JavaType baseType,
Collection<NamedType> subtypes) {
//Copied this code from parent class, StdTypeResolverBuilder with same method name
TypeIdResolver idRes = idResolver(config, baseType, subtypes, false, true);
return new NestedTypeDeserializer(baseType, idRes, _typeProperty, _typeIdVisible,
null, _includeAs);
}
}
所有繁重的工作都在这里完成,NestedTypeDeserializer:
/**
* Heavy work to support {@link NestedTypeResolver}
*/
public class NestedTypeDeserializer extends AsPropertyTypeDeserializer {
private static final Logger LOGGER = LoggerFactory.getLogger(NestedTypeDeserializer.class);
public NestedTypeDeserializer(JavaType bt,
TypeIdResolver idRes, String typePropertyName, boolean typeIdVisible,
JavaType defaultImpl) {
super(bt, idRes, typePropertyName, typeIdVisible, defaultImpl);
}
public NestedTypeDeserializer(JavaType bt, TypeIdResolver idRes, String typePropertyName, boolean typeIdVisible,
JavaType defaultImpl, JsonTypeInfo.As inclusion) {
super(bt, idRes, typePropertyName, typeIdVisible, defaultImpl, inclusion);
}
public NestedTypeDeserializer(AsPropertyTypeDeserializer src, BeanProperty property) {
super(src, property);
}
@Override
public TypeDeserializer forProperty(BeanProperty prop) {
return (prop == _property) ? this : new NestedTypeDeserializer(this, prop);
}
@Override
public Object deserializeTypedFromObject(JsonParser p, DeserializationContext ctxt) throws IOException {
JsonNode originalNode = p.readValueAsTree();
JsonNode node = originalNode;
//_typePropertyName is the dot separated value of "property" in @JsonTypeInfo
LOGGER.debug("Searching for type discriminator [{}]...", _typePropertyName);
for (String property : _typePropertyName.split("\\.")) { //traverse down any nested properties
JsonNode nestedProp = node.get(property);
if (nestedProp == null) {
ctxt.reportWrongTokenException(p, JsonToken.FIELD_NAME,
"missing property '" + _typePropertyName + "' that is to contain type id (for class "
+ baseTypeName() + ")");
return null;
}
node = nestedProp;
}
LOGGER.debug("Found [{}] with value [{}]", _typePropertyName, node.asText());
JsonDeserializer<Object> deser = _findDeserializer(ctxt, "" + node.asText());
//Since JsonParser is a forward-only operation and finding the "type" discriminator advanced the pointer, we need to reset it
//Got clues from https://www.dilipkumarg.com/dynamic-polymorphic-type-handling-jackson/
JsonParser jsonParser = new TreeTraversingParser(originalNode, p.getCodec());
if (jsonParser.getCurrentToken() == null) {
jsonParser.nextToken();
}
return deser.deserialize(jsonParser, ctxt);
}
}
免责声明:我们已经在 Jackson 2.8.10 上使用了一个月,没有遇到任何问题,但我们必须深入研究 Jackson 源代码杂草才能完成它,所以 YMMV。 希望 Jackson 有一天会允许这种开箱即用的方式,这样我们就不需要这些解决方法了。
关于java - 什么@JsonTypeInfo.ID选择属性= "type.id"反序列化,JsonTypeInfo.Id.CUSTOM?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25671806/