Using Gson convert Java object into JsonObject

Question

I have a Java object, and I want to output it as a JSON string. BUT I want to avoid printing out a property in the Java object. I know that I could do this using GsonBuilder's excludeFieldsWithoutExposeAnnotation() method. However, I thought I'd try the alternate approach of removing the property from the JsonObject before printing it out. The following code works:

Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd' 'HH:mm:ss").create();
String javaObjectString = gson.toJson(javaObject);
//javaObjectString currently include "property":"value"
JsonElement jsonElement = gson.toJsonTree(javaObjectString, javaObject.getClass());
JsonObject jsonObject = (JsonObject) jsonElement;
jsonObject.remove("property");
javaObjectString = gson.toJson(jsonObject);
//javaObjectString currently no longer includes "property":"value"

However, it feels a but hacky because I have to output the Java object to a String, and then create a JsonElement from the String, and then cast the JsonElement to a JsonObject.

Is there a more direct way to go from a Java object to a JsonObject?

Answer 1

You don't need the intermediary String. Serialize your Java object to a JsonElement directly with Gson#toJsonTree(Object). Cast that value to whatever type you expect (JSON object, array, or primitive), perform your removal and invoke its toString() method to retrieve its JSON representation as a String.

For example,

Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd' 'HH:mm:ss").create();
// JSON data structure
JsonElement jsonElement = gson.toJsonTree(javaObject);
JsonObject jsonObject = (JsonObject) jsonElement;
// property removal
jsonObject.remove("property");
// serialization to String
String javaObjectString = jsonObject.toString();

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You can always use the Gson#toJson overload that accepts a JsonElement to serialize it directly to a stream if you want to skip that last String object creation.