GSON : Custom serialization for String

Question

public class Data{
     public String str;  //String (that may contain line breaks) I need to serialize as it is.
}

Why I needed custom Serializer for string? Without custom serializer it serializes this as object {"str":{"count": 292,"hashCode": 0} }

I need it to be {"str":"..............."}

How to do it with custom Serializer?

There are example of custom serializer for custom types, but could not find anything that helps to serialize String type.

score 1 · Answer 1 · answered Sep 23 '19 at 14:38

Well, Gson supports strings out of box and you don't have to implement any string serializer and vice versa yourself. What I guess might happen to your case is merely importing a wrong string class, say import foo.bar.baz.String; or less obvious import foo.bar.baz.*, or you just have a String class implementation right in the package where your Data class is declared in. (This cannot explain what values were really assigned to str, though, -- it would never work in Java causing ClassCastException). A wrong class might be indicated with numeric count and hashCode without any char[]-declared fields, so I don't believe this is a java.lang.String in your case. Also, a more hypothetical thing here might be use of reflection that discarded the string type adapter out of your Gson instance, no matter how and how weird it sounds. In any case, you don't have to implement even a single line to serialize Java strings with Gson.

Regarding the accepted answer: it is suboptimal. If, for whatever reason, there is nothing wrong with your imports, your package does not declare a custom String class, and your Gson instances do not suffer from reflection surgery, but Gson still serializes such strings as nested objects (have no ideas why then), you'd only need a single special String type adapter without any need of creating type adapters for any class that uses that weird String as a field:

final Gson gson = new GsonBuilder()
    .registerTypeAdapter(/*real.package.here.*/String.class, (JsonSerializer</*real.package.here.*/String>) (s, type, context) -> new JsonPrimitive(s.toString())) // whatever the real Java string is obtained
    .create();

score 0 · Accepted Answer · answered Sep 23 '19 at 09:13

0

Try this

public class DataSerializer implements JsonSerializer<Data> {


        @Override
        public JsonElement serialize(Data data, Type typeOfSrc, JsonSerializationContext context) {

            JsonObject object = new JsonObject();
            object.addProperty("src",  data.src);

            return object;
        }
 }

Add this to Gson Like this

Gson gson = new GsonBuilder()
.registerTypeAdapter(Data.class, new DataSerializer())
.create();

answered Sep 23 '19 at 09:13

Oshan Madusanka

327
3
9

What if Model class has more fields, it will also need to manage by DataSerializer class right? – LaraFlow Sep 23 '19 at 09:41
What may be the reason field String str being treated as Object, instead String? – LaraFlow Sep 23 '19 at 09:46
field String str treated as JSON because it's value is in JSON format – Oshan Madusanka Sep 23 '19 at 10:01
Yes it may be valid Json format string, but it is string type of data on model. Is there any way to treat it as string with annotation or just simple without writing DataSerializer for entire Data class – LaraFlow Sep 23 '19 at 10:10
https://stackoverflow.com/a/11272452/8166037 check out this answer. It could help your problem. – Oshan Madusanka Sep 23 '19 at 11:20

GSON : Custom serialization for String

2 Answers2