JsonTypeInfo not supported when the instance is inside a Map?

[Rich MacDonald]

I am finding that instances with a JsonTypeInfo annotation are not written with a @class property when the instance is inside a HashMap.

Here is my test code:

------------------------------------------------------------------------------------------------

package test;

import java.util.HashMap;

import com.fasterxml.jackson.annotation.JsonAnyGetter;

import com.fasterxml.jackson.annotation.JsonAnySetter;

import com.fasterxml.jackson.annotation.JsonIgnore;

import com.fasterxml.jackson.annotation.JsonInclude;

import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS)

public class JsonAttributes {

public JsonSub subAsProperty;

@JsonIgnore

public HashMap<String,Object> dynamicAttrs = new HashMap<String,Object>();

@JsonInclude

public HashMap<String,Object> explicitAttrs = new HashMap<String,Object>();

@JsonAnyGetter

public HashMap<String,Object> jsonGet(){

return dynamicAttrs;

}

@JsonAnySetter

public void jsonSet(String key, Object value){

dynamicAttrs.put(key, value);

}

}

------------------------------------------------------------------------------------------------

package test;

import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS)

public class JsonSub {

public String str;

public JsonSub() {}

public JsonSub(String string) {

str = string;

}

}

------------------------------------------------------------------------------------------------

package test;

import java.io.IOException;

import com.fasterxml.jackson.core.JsonGenerationException;

import com.fasterxml.jackson.databind.JsonMappingException;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Test {

public static void main(String[] args) throws JsonGenerationException, JsonMappingException, IOException {

JsonAttributes json = new JsonAttributes();

json.dynamicAttrs.put("subInDynamic", new JsonSub("sub inside anyGetter"));

json.explicitAttrs.put("subInExplicit", new JsonSub("sub inside explicit map"));

json.subAsProperty = new JsonSub("sub as property");

ObjectMapper mapper = new ObjectMapper();

String str = mapper.writeValueAsString(json);

System.out.println(str);

JsonAttributes readJson = mapper.readValue(str, JsonAttributes.class); //this succeeds

//However, the subInDynamic JsonSub class is read as a HashMap

System.err.println("subInDynamic class type = "+readJson.dynamicAttrs.get("subInDynamic").getClass().getName());

}

}

------------------------------------------------------------------------------------------------

The result is:

{

"@class": "test.JsonAttributes",

"subAsProperty": {

"@class": "test.JsonSub",

"str": "sub as property"

},

"explicitAttrs": {

"subInExplicit": {

"str": "sub inside explicit map"

}

},

"subInDynamic": {

"str": "sub inside anyGetter"

}

}

And:

subInDynamic class type = java.util.LinkedHashMap

Note that the @class property for the JsonSub instance is only written when the property is explicitly of type JsonSub.

When the JsonSub instance is inside a Map, the @class property is not written.

And therefore, when the JsonAttributes is instantiated, the subInDynamic instance is now a LinkedHashMap, rather than a JsonSub.

This isn't my desired behavior.

I figured that jackson would inspect any instance it was serializing and would write the @class property if it found a JsonTypeInfo annotation.

Is there any way to get around this behavior, or have I made a mistake? TIA

[Tatu Saloranta]

If I read the example correctly, I think your problem is due to incomplete type declaration for maps. Both explicit map and implicit 'any' map declare values to be of type `java.lang.Object`, and since this base type is used to check for @JsonTypeInfo, it is assumed values do not have type info.

The fact that some subtypes do is not considered; base type must define type info inclusion criteria.

But there should be an easy fix at least for explicit map.

You can and need to add @JsonTypeInfo for Map-valued property, like:

@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS)

@JsonInclude

public HashMap<String,Object> explicitAttrs = new HashMap<String,Object>();

Alternatively if possible, you would use more specific base value class; this would be needed for "any" setter case.

Yet another possibility would be to enable "default typing" feature, but that would apply to all values, not just those of explicit/implicit maps you use.

-+ Tatu +-

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