Jackson Deserialize JSON To List of Different Types Depending On String Value

Question

I need to deserialize a JSON string using Jackson into Lists of different Object types depending on the value set in one of the fields. I want to know what the best approach is for creating the different List Types and how i can implement this?

My JSON's would look something like this:

{"test":
    {"conditions":[....],                   
     "consequence": {"actionType":"string", 
                     "action": ["value 1","value 2"]}                                               
    }       
}

So when parsed the above would return a List<String>

{"test":
    {"conditions":[....],                   
     "consequence": {"actionType":"test", 
                     "action": ["test","test"]}                                             
    }       
}

and the above would return a List<Test>

My Pojo just contains:

  @Data
public class Consequence {

    public Consequence(String actionType){
        this.actionType = actionType;       
    };

    @JsonProperty("ACTIONTYPE")
    private String actionType;

    @JsonProperty("ACTION")
    private List<????> action;
}

UPDATE:

After i updated my POJO's using the following hierarchy:

@Data
public abstract class BaseConsequence {

    public BaseConsequence(String actionType){
        this.actionType = actionType;       
    };

    @JsonProperty("ACTIONTYPE")
    private String actionType;

}

 @Data
@DiscriminatorValue(value = "CONCATENATE")
public class ConcatenateConsequence extends BaseConsequence {

    public ConcatenateConsequence(String actionType, List<String> concatenateValues) {
        super(actionType);
        this.concatenateValues = concatenateValues;
    }
    private List<String> concatenateValues;
}

@Data
@DiscriminatorValue(value = "test")
public class TestConsequence extends BaseConsequence {

    public TestConsequence(String actionType, List<Test> tests){
        super(actionType);
        this.tests = tests;
    }
    private List<Test> tests;
}

@Data
public class Test {

    public Test(){};

    public Test(List<Condition> conditions, BaseConsequence baseConsequence){
        this.conditions = conditions;
        this.baseConsequence = baseConsequence;     
    }

    @JsonProperty("CONDITIONS")
    private List<Condition> conditions;

    @JsonProperty("CONSEQUENCE")
    private BaseConsequence baseConsequence;

    @Override
    public boolean equals(Object o) {

        if (o == this) return true;

        if (!(o instanceof Test)) {
            return false;
        }        
        Test test = (Test) o;
        return Objects.equals(conditions, test.conditions) && Objects.equals(baseConsequence, test.baseConsequence);
    }

    @Override
    public int hashCode() {
        return Objects.hash(conditions, baseConsequence);
    }   
}

I get the following error:

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
 at [Source: {"TEST":{"CONDITIONS":[{"KEY":"KEY1","VALUES":["FLOAT"],"OPERATOR":""}],"CONSEQUENCE":{"ACTIONTYPE" :{"CONCATENATE": ["VALUE1","VALUE2"]}}}}; line: 1, column: 9] (through reference chain: package.TestCase["TEST"])

Answer 1

There are two variants you can use:

1. Create custom deserializer. See here for full descriptions and examples http://www.baeldung.com/jackson-deserialization
2. The best way is to use one base class and two children. Each children should be marked with @DiscriminatorValue . See here for full description and examples http://www.baeldung.com/jackson-inheritance