使用GSON创建JSON字符串

Question

我正在上课,

public class Student {
    public int id;
    public String name;
    public int age;    
}

现在我要创建新学生,

//while create new student
Student stu = new Student();
stu.age = 25;
stu.name = "Guna";
System.out.println(new Gson().toJson(stu));

这给了我以下输出,

{"id":0,"name":"Guna","age":25} //Here I want string without id, So this is wrong

所以我在这里想要String

{"name":"Guna","age":25}

如果我想编辑旧学生

//While edit old student
Student stu2 = new Student();
stu2.id = 1002;
stu2.age = 25;
stu2.name = "Guna";
System.out.println(new Gson().toJson(stu2));

现在输出是

{"id":1002,"name":"Guna","age":25} //Here I want the String with Id, So this is correct

如何使用字段[在某些时候]创建一个JSON字符串,没有字段[在某些时候].

任何帮助都会非常值得一提.

谢谢.

Answer 1

更好的是使用@expose注释

public class Student {
    public int id;
    @Expose
    public String name;
    @Expose
    public int age;
}

并使用下面的方法从您的对象获取Json字符串

private String getJsonString(Student student) {
    // Before converting to GSON check value of id
    Gson gson = null;
    if (student.id == 0) {
        gson = new GsonBuilder()
        .excludeFieldsWithoutExposeAnnotation()
        .create();
    } else {
        gson = new Gson();
    }
    return gson.toJson(student);
}

如果将其设置为0,它将忽略id列,它将返回带有id字段的json字符串.