java - 使用 Gson 反序列化映射键需要一个对象

Question

我得到错误:

Exception in thread "main" com.google.gson.JsonParseException: 
Expecting object found: "com.shagie.app.SimpleMap$Data@24a37368"

当尝试反序列化使用非平凡键的 Map 时:

package com.shagie.app;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.HashMap;

public class SimpleMap {
    public static void main(String[] args) {
        Wrapper w = new Wrapper();
        w.m.put(new Data("f", 1), new Data("foo", 3));
        w.m.put(new Data("b", 2), new Data("bar", 4));

        GsonBuilder gb = new GsonBuilder();
        gb.setPrettyPrinting();
        Gson g = gb.create();

        String json = g.toJson(w);

        System.out.println(json);

        w = g.fromJson(json, Wrapper.class);
        System.out.println(w.m.isEmpty());
    }

    static public class Wrapper {
        HashMap<Data, Data> m = new HashMap<Data, Data>();
    }

    static public class Data {
        String s;
        Integer i;
        public Data(String arg, Integer val) { s = arg; i = val; }
    }
}

这会序列化为 json:

{
  "m": {
    "com.shagie.app.SimpleMap$Data@24a37368": {
      "s": "foo",
      "i": 3
    },
    "com.shagie.app.SimpleMap$Data@66edc3a2": {
      "s": "bar",
      "i": 4
    }
  }
}

可以看到尝试序列化的 key ，但肯定不是以可以反序列化的方式。

如何序列化此对象以便反序列化？

Answer 1

我在尝试解决这个难题时发现了以下内容:Issue 210: Cannot serialize or deserialize Maps with complex keys .

For any internet travelers from the future (like myself)... you can enable this functionality in GSON 2.* with the enableComplexMapKeySerialization() method on GsonBuilder.

这是 javadoc for that method .

启用后， map 将被序列化(并正确反序列化)为 [key, value] 数组的数组:

{"m":[[{"s":"f", "i",1}, {"s":"foo", "i":3}], [{"s":"b", "i",2}, {"s":"bar", "i":4}]]}