gson自定义反序列化器

写在前面

gson提供了一套强大的序列化、反序列化器。但某些场景下,如反序列化父子类时,gson现成反序列化器只能识别到父类的属性信息,子类属性会丢失。 普通的反序列化器是不能用的。需要自定义反序列化器,强加自己的业务逻辑。不是闲着蛋疼去实现自定义的序列化器。

举个栗子

school对象

public class School {

    private String name;

    private List<People> peopleList;
}    

父类

public class People {

    private String name;

    private int age;
}    

子类

public class Student extends People {

    private Long cardId;
}

直接用gson现成的反序列化器

public static void main(String[] args) {

        List<People> peopleList = Lists.newArrayList();

        Student student = new Student("威少", 20, 666666L);
        peopleList.add(student);

        School school = new School("实验", peopleList);

        String json = gson.toJson(school);

        School r = gson.fromJson(json, School.class);

        System.out.println(gson.toJson(r));
}

结果 ：

{
  "name": "实验",
  "peopleList": [
    {
      "name": "威少",
      "age": 20
    }
  ]
}

如此一来,我们可以看出来,用gson默认的反序列化器,是会丢失student的cardId属性信息的。下面我们来解决这个问题

自定义反序列化器

• 实现接口 JsonDeserializer

重写方法
        @Override
        public VideoTemplate deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException

• 完成demo

public class JsonDeserializerDemo {

    /**
     * special gson
     */
    private final static Gson gson;

    static {
        GsonBuilder gsonBuilder = new GsonBuilder();
        JsonDeserializer<School> deserializer = new DefineDeserializer();
        gsonBuilder.registerTypeAdapter(School.class, deserializer);
        gson = gsonBuilder.create();
    }

    public static class DefineDeserializer implements JsonDeserializer<School> {

        @Override
        public School deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {

            School school = new School();

            JsonObject jsonObject = json.getAsJsonObject();
            JsonElement name = jsonObject.get("name");
            school.setName(name.getAsString());

            List<People> peopleList = new ArrayList<>();
            school.setPeopleList(peopleList);

            JsonArray jsonArray = json.getAsJsonObject().get("peopleList").getAsJsonArray();
            for(JsonElement jsonElement : jsonArray) {

                JsonObject asJsonObject = jsonElement.getAsJsonObject();
                String stuName = asJsonObject.get("name").getAsString();
                Long cardId = asJsonObject.get("cardId").getAsLong();
                int age = asJsonObject.get("age").getAsInt();

                Student student = new Student(stuName, age, cardId);
                peopleList.add(student);
            }

            return school;
        }
    }

    public static void main(String[] args) {

        List<People> peopleList = Lists.newArrayList();

        Student student = new Student("威少", 20, 666666L);
        peopleList.add(student);

        School school = new School("实验", peopleList);

        String json = gson.toJson(school);

        School r = gson.fromJson(json, School.class);

        System.out.println(gson.toJson(r));


    }
}

result

{
  "name": "实验",
  "peopleList": [
    {
      "cardId": 666666,
      "name": "威少",
      "age": 20
    }
  ]
}