Gson序列化Map对象键后反序列化报错，求正确实现方案

问题根源：Gson默认会将非基本类型的Map键转为字符串（调用对象的toString()方法），反序列化时无法将该字符串还原为自定义对象，导致JsonSyntaxException。必须为作为Map键的Chunk和Location类自定义TypeAdapter，指定序列化/反序列化规则。

步骤1：为Chunk类编写TypeAdapter #

利用Chunk的final字段生成唯一标识字符串，反序列化时解析字符串重建对象：

public class ChunkTypeAdapter extends TypeAdapter<Chunk> {
    @Override
    public void write(JsonWriter out, Chunk chunk) throws IOException {
        // 用无冲突分隔符拼接字段，生成键字符串
        String key = chunk.getWorldName() + "|" + chunk.getX() + "|" + chunk.getZ();
        out.value(key);
    }

    @Override
    public Chunk read(JsonReader in) throws IOException {
        String key = in.nextString();
        String[] parts = key.split("\\|");
        String worldName = parts[0];
        int x = Integer.parseInt(parts[1]);
        int z = Integer.parseInt(parts[2]);
        return new Chunk(worldName, x, z);
    }
}

步骤2：为Location类编写TypeAdapter #

逻辑与Chunk一致，多处理一个y字段：

public class LocationTypeAdapter extends TypeAdapter<Location> {
    @Override
    public void write(JsonWriter out, Location location) throws IOException {
        String key = location.getWorldName() + "|" + location.getX() + "|" + location.getY() + "|" + location.getZ();
        out.value(key);
    }

    @Override
    public Location read(JsonReader in) throws IOException {
        String key = in.nextString();
        String[] parts = key.split("\\|");
        String worldName = parts[0];
        int x = Integer.parseInt(parts[1]);
        int y = Integer.parseInt(parts[2]);
        int z = Integer.parseInt(parts[3]);
        return new Location(worldName, x, y, z);
    }
}

步骤3：注册TypeAdapter并创建Gson实例 #

将自定义TypeAdapter注册到GsonBuilder，覆盖默认的键处理逻辑：

Gson gson = new GsonBuilder()
        .registerTypeAdapter(Chunk.class, new ChunkTypeAdapter())
        .registerTypeAdapter(Location.class, new LocationTypeAdapter())
        .create();

步骤4：修改序列化/反序列化方法 #

使用自定义Gson实例处理Map：

// 保存方法
public void saveChests(Map<Chunk, LinkedHashMap<Location, ChestObject>> chestMap, String filePath) throws IOException {
    try (FileWriter writer = new FileWriter(filePath)) {
        gson.toJson(chestMap, writer);
    }
}

// 恢复方法
public Map<Chunk, LinkedHashMap<Location, ChestObject>> recoverChests(String filePath) throws IOException {
    try (FileReader reader = new FileReader(filePath)) {
        Type type = new TypeToken<Map<Chunk, LinkedHashMap<Location, ChestObject>>>() {}.getType();
        return gson.fromJson(reader, type);
    }
}

可选优化：用JSON字符串作为键 #

如果担心字段包含分隔符，可将对象序列化为JSON字符串作为键，更通用：

// ChunkTypeAdapter的替代实现
public class ChunkTypeAdapter extends TypeAdapter<Chunk> {
    private final Gson internalGson = new Gson();

    @Override
    public void write(JsonWriter out, Chunk chunk) throws IOException {
        String json = internalGson.toJson(chunk);
        out.value(json);
    }

    @Override
    public Chunk read(JsonReader in) throws IOException {
        String json = in.nextString();
        return internalGson.fromJson(json, Chunk.class);
    }
}

内容的提问来源于stack exchange，提问作者HowDoISolveThis