如何使用Jackson将地图地图转换为POJO

Question

I have a Map which contains another Map as follows:

private ObjectMapper mapper;
private Map<String,Map<String,Long>> indicatorsList;

How can I use Jackson in order to convert it to POJO?

This is what I was trying to do:

public Map<String,Map<String,Long>> calculateIndicators(List<indicatorsDAO> events){

        Map<String,Map<String,Long>> indicatorsCountersMap=
            events.stream().collect(
                Collectors.groupingBy(
                    indicatorsDAO::getType,
                    Collectors.groupingBy(
                        indicatorsDAO::getLight,
                        Collectors.counting())
                )
            );

       return mapper.convertValue(indicatorsCountersMap,Indicators.class);

    }

This is Indicators class:

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Indicators{
    private Map<String,Map<String,Long>> indicatorsList;
}

The results of this conversion is: null

This is how the map should look like, just an example:

    "indicatorsList": {
        "Bulb": {
          "Green": 2,
          "Red": 3
        },
        "Led": {
          "Red": 1
        }
}

Answer 1

Try to use the below code snippet to convert your MAP object the JSON string.

ObjectMapper mapperObj = new ObjectMapper();
String jsonStr = StringUtils.EMPTY;

try {
    jsonStr = mapperObj.writeValueAsString(<<MAP OBJECT>>);
}
 catch (IOException e) { 
 e.printStackTrace();
}