GSON Java Object 序列化

Question

I am writing a object to JSON file. Want to know how can I add parent element in object OR just add parent element in JSON file.

    public void writeToJSON(Path dest, Student studentJSON) throws IOException {
        Gson gson = new GsonBuilder().serializeNulls().setPrettyPrinting().create();
        try (PrintWriter wr = new PrintWriter(Files.newBufferedWriter(dest))) {
        gson.toJson(studentJSON, wr);
    }

This produces student list in Json as

{
    "students": [
          {
            "Name": "foo",
            "Grade": "A"
          },
          {
            "Name": "bar",
            "Grade": "B+",
          }
    ]
}

I am looking for a JSON like this:

{
    "class" : {
        "students": [
              {
                "Name": "foo",
                "Grade": "A"
              },
              {
                "Name": "bar",
                "Grade": "B+",
              }
        ]
    }
}

I don't want to create an additional class for this. Any idea how can I change my write function or if GSON provides any property for this?

Answer 1

You have to modify you method to look like this

public static void writeToJSON(Path dest, List<Student> studentJSON) throws IOException {
        Gson gson = new GsonBuilder().serializeNulls().setPrettyPrinting().create();
        try (PrintWriter wr = new PrintWriter(Files.newBufferedWriter(dest))) {
            JsonElement jsonElement = gson.toJsonTree(studentJSON);
            JsonObject classObject = new JsonObject();
            JsonObject studentsObject = new JsonObject();
            studentsObject.add("students", jsonElement);
            classObject.add("class", studentsObject);
            gson.toJson(classObject, wr);
        }
    }

Student POJO class

class Student {
        public Student(String name, String grade) {
            this.name = name;
            this.grade = grade;
        }

        @SerializedName("Name")
        String name;
        @SerializedName("Grade")
        String grade;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getGrade() {
            return grade;
        }

        public void setGrade(String grade) {
            this.grade = grade;
        }
    }

This is how would you class it fo

List<Student> students = new ArrayList<>();
students.add(new Student("silentsudo", "A+"));
students.add(new Student("random", "C+"));
writeToJSON(Paths.get("/home/usertest.json"), students);

Explanation:

• Create Json object for class .
• Create json Object for student .
• Compose students JsonElement using string.
• Put students in studentJosn Object
• Put student jsonObject into class