Hello!
I'm trying to write a custom serializer that can transform the following
structure
{
"a": {
"@context": "context-a",
"aKey": "aValue"
},
"b": {
"@context": "context-b",
"anotherbKey": "anotherbValue",
"bKey": "bValue"
}
}
into this:
{
"@context" : ["context-a", "context-b"],
"a": {
"aKey": "aValue"
},
"b": {
"anotherbKey": "anotherbValue",
"bKey": "bValue"
}
}
The reason to do this is to put all json-ld headers at the beginning of the
serialized json. I have a utility class that extract all @context attribute
from a bean hierarchy (ContextsCrawler in the snippet below) and my current
serializer attempt is this:
public class JsonLdModelSerializer extends JsonSerializer<Object> {
private static Optional<String> baseContext;
private static ContextsCrawler ctxCrawler = new ContextsCrawler();
public static void scanClassForContexts(Map<Class<?>, Class<?>> mixins)
{
ctxCrawler.scanClassForContexts(mixins);
}
public static void setBaseContext(String baseContext) {
JsonLdModelSerializer.baseContext = Optional.of(baseContext);
}
@Override
public void serialize(Object value, JsonGenerator jgen,
SerializerProvider serializers)
throws IOException, JsonProcessingException {
jgen.writeStartObject();
// Add contexts elements in top level element only:
if (jgen.getOutputContext().getParent().inRoot()) {
Collection<String> cxts = ctxCrawler.getContexts(value);
if (cxts != null) {
Set<String> ctxset = new HashSet<>();
baseContext.ifPresent(ctx -> ctxset.add(ctx));
ctxset.addAll(cxts);
jgen.writeObjectField("@context", ctxset);
}
}
JavaType javaType = serializers.constructType(value.getClass());
BeanDescription beanDesc = serializers.getConfig().introspect(
javaType);
JsonSerializer<Object> serializer = BeanSerializerFactory.instance.
findBeanSerializer(serializers,
javaType,
beanDesc);
serializer.unwrappingSerializer(null).serialize(value, jgen,
serializers);
jgen.writeEndObject();
}
}
Then I simply define a mixin for each class that contains a @context
element like this:
@JsonSerialize(using = JsonLdModelSerializer.class)
@JsonIgnoreProperties("context")
public class CapabilityMixIn extends Capability {
@Override
@JsonLdContextProvider // used by ContextsCrawler
public List<String> getContext() {
return super.getContext();
}
}
It works but it has two main problems:
1. I don't know it the direct usage of BeanSerializerFactory in serialize
method is OK since I read that this is not the best approach to use. I'm
also worried about performance implications;
2. For some reason this serializer doesn't play nice with beans that
contains Map<String,Object> that are decorated with @JsonAnyGetter: the
resulting json does not contain the map elements
Could you please provide guidance? What is the right approach to implement
such a JsonLdModelSerializer?
Thank you,
Matteo
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