java - 如何使用 Gson 序列化包含 HashMap 作为属性的类？还反序列化？

Question

我想序列化一个包含 HashMap 的类，并且 hHashHap 有一个类键。但出了问题。

    public class Buyer {
        private long wallet;
        private HashMap<Discount, Integer> discountCodes;
    }

当我使用toJson方法时

"discountCodes":{"model.Discount@18769467":1,"model.Discount@1cf4f579":2}

它是这样序列化的，所以在反序列化时会导致错误

Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 34 path $[0].discountCodes.

我的意思是如何将Buyer的对象转换为json而不是转换HashMap

Answer 1

1. 将包含泛型类型的 HashMap 序列化为 JSON

HashMap<Integer, Employee> employeeMap = new HashMap<>();

employeeMap.put(1, new Employee(1l, "Alex", LocalDate.of(1990, 01, 01)));
employeeMap.put(2, new Employee(2l, "Bob", LocalDate.of(1990, 02, 01)));

//Deep clone
Gson gson = new Gson();
String jsonString = gson.toJson(employeeMap);

生成的json:

{
  "1": {
    "id": 1,
    "name": "Alex",
    "dob": {
      "year": 1990,
      "month": 1,
      "day": 1
    }
  },
  "2": {
    "id": 2,
    "name": "Bob",
    "dob": {
      "year": 1990,
      "month": 2,
      "day": 1
    }
  }
}

将 JSON 转换为包含自定义对象的 HashMap

        HashMap<Integer, Employee> employeeMap = new HashMap<>();

        employeeMap.put(1, new Employee(1l, "Alex", LocalDate.of(1990, 01, 01)));
        employeeMap.put(2, new Employee(2l, "Bob", LocalDate.of(1990, 02, 01)));

        //Deep clone
        Gson gson = new Gson();
        String jsonString = gson.toJson(employeeMap);

        Type type = new TypeToken<HashMap<Integer, Employee>>(){}.getType();
        HashMap<Integer, Employee> clonedMap = gson.fromJson(jsonString, type);