Jackson - converting java object to json - Need all key keys to upper case

Question

Need your help on conversion of java objects to json. current the json result showing all the key in small letter case, i need it to be upper case.

ObjectMapper mapper = new ObjectMapper();
Writer strWriter = new StringWriter();
mapper.writeValue(strWriter, obj);
String jsonString= strWriter.toString();

and the result is

[{"flags":"1","name":"Peter","location":"London","startDate":"2012-01-06 00:00"}]

but i want results like this (all key key value should be in UPPER CASE):

[{"FLAGS":"YU","NAME":"Peter","LOCATION":"London","STARTDATE":"2012-01-06 00:00"}]

and also is it possible to get like this also (key first letter in upper case):

[{"Flags":"1","Name":"Peter","Location":"London","StartDate":"2012-01-06 00:00"}]

Can anyone help me on this.

Thanks in advance.

Answer 1

There are multiple ways to do it with Jackson.

Annotations

You could annotate your object with @JsonProperty annotations on your fields or on your getter methods.

Example:

@JsonProperty("Name")
public final String name;

@JsonProperty("Location")
public String getLocation() {
  return location;
}

Implement JsonSerializableWithType interface

@Override
public void serialize(final JsonGenerator jG, final SerializerProvider p)
    throws IOException, JsonProcessingException
{
    serializeWithType(jG, p, null);
}

@Override
public void serializeWithType(final JsonGenerator jG, final SerializerProvider p, final TypeSerializer typeSer)
    throws IOException, JsonProcessingException
{
    // here you can do your own serialization
}

Answer 2

I would advice to use the @JsonNaming annotation on class level.

Yet afaik there is no strategy out there to fit your needs for total uppercase. But you can probably just write your own.

In my case I needed first character uppercase. So I used the existing @JsonNaming(value = UpperCamelCaseStrategy.class).