如何序列化包含 HashMap 的类作为 Gson 的属性? 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。 但它出错了。

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}

它像这样序列化，所以在反序列化导致错误

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.

我的意思是如何将买方的对象转换为json 而不转换哈希映射

Answer 1

1. 将包含泛型类型的哈希映射序列化为 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
}
}
}

2. >将 JSON 转换为包含自定义对象的哈希映射

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);