How can I use a property of Java Enum when converting to JSON

Question

I'm having some difficulty in translating a certain Java Enum to JSON. I have the following Enum:

public enum Color {
    BLUE("Blue"), RED("Red");
    private String colorName;

    Color(final String colorName) {
        this.colorName = colorName;
    }

    @Override
    public String toString() {
        return colorName;
    }
}

When converting to JSON, I'd like to use the name, so I've overridden the toString method. I thought that was enough, but when I do this test:

Gson gson = new Gson();
assertEquals("Blue", gson.toJson(Color.BLUE));

It fails! It gives me "BLUE"... is there any way I can make the thing return "Blue"?

I've also tried the @JsonValue annotation on a method that returns the name but to no result. The fasterxml @JsonFormat also give me nothing...

Answer 1

first of all, even if it's not the cause avoid naming the attribut name.

otherwise, change your code like this and it will work.

public enum Color {
@SerializedName("Blue") BLUE("Blue"),
@SerializedName("Red") RED("Red");
    private String name;

    Color(final String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return name;
    }
}

Answer 2

@JsonValue on method that returns name to use does work. Just make sure that you are not accidentally using wrong Jackson annotations (Jackson 2.x requires annotations from com.fasterxml.jackson.annotation ; Jackson 1.x ones from org.codehaus.jackson ). Also, if you are using an old Jackson version, try upgrade; support for @JsonValue was added somewhere around 2.4 I think.

Answer 3

I found the solution myself, but StaxMan made me persist in trying :)

What I did was adding an annotation from Jackson 2.x, but in my tests I used Gson to convert to json. These don't play together. So when you're using Jackson to define the json output, also use Jackson to convert your object to json:

public class ColorTest {

    @Test
    public void convertToJson() throws JsonProcessingException {
        ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
        String json = ow.writeValueAsString(Colors.BLUE);
        assertEquals("\"blue\"", json);
    }

    private enum Colors {
        RED("red"), BLUE("blue");

        private String colorName;

        Colors(final String colorName) {
            this.colorName = colorName;
        }

        @JsonValue
        @Override
        public String toString() {
            return colorName;
        }
    }
}

Works like a charm!