HashMap（key，Object）中的Java Gson序列化和反序列化对象[重复]

Question

我有以下代码作为我想要实现的示例：

public static void main(String args[]) {

    Map<String, Object> map = new HashMap<String, Object>();
    map.put("1", new A());  
    map.put("2", new B());
    String json = new Gson().toJson(map);
    Type type = new TypeToken<Map<String, Object>>(){}.getType();
    map = new Gson().fromJson(json, type);
    A a = (A) map.get("1"); 
    B b = (B) map.get("2");

}

static class A {

    int inum = 1;
    double dnum = 1.0;
    String str = "1";

}

static class B {

    int inum = 2;
    double dnum = 2.0;
    String str = "2";

}

以下代码导致此异常：

Exception in thread "main" java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to ParseJson$A
    at ParseJson.main(ParseJson.java:19)

所以问题是： 如何在被 Gson 序列化和反序列化的通用 HashMap 中获取正确的实例？

Answer 1

Object 被反序列化为com.google.gson.internal.LinkedTreeMap，所以告诉Gson 你想要A 类。

public static void main(String args[]) {
    Map<String, Object> map = new HashMap<>();
    map.put("1", new A());
    String json = new Gson().toJson(map);
    Type type = new TypeToken<Map<String, A>>() {
    }.getType();
    map = new Gson().fromJson(json, type);
    A a = (A) map.get("1");
    System.out.println(a.str);
}

static class A {
    private int num1 = 1;
    private double num2 = 2.0;
    private String str = "String";
}

希望对你有帮助。

更新

基类（在这种情况下为X）可能是一个解决方案：

public static void main(String args[]) {
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("1", new A());
    map.put("2", new B());
    String json = new Gson().toJson(map);
    Type type = new TypeToken<Map<String, X>>(){}.getType();
    map = new Gson().fromJson(json, type);
    X a = (X) map.get("1");
    X b = (X) map.get("2");
    System.out.println(a.str);
    System.out.println(b.str);
}

static class X {
    int inum;
    double dnum;
    String str;

    X() {
    }
}

static class A extends X {
    A() {
        inum = 1;
        dnum = 1.0;
        str = "1";
    }
}

static class B extends X {
    B() {
        inum = 2;
        dnum = 2.0;
        str = "2";
    }
}