從JSON文件到Java類的GSON映射

Question

我想將JSON文件映射到我在Java中創建的一組類。我試圖完成的小背景。我想要一個「鍋 - >種子 - >收穫籃子 - >收穫項目」，其中： 鍋：黃銅，粘土，木 種子：穀物，水果 收穫籃子:(一鍋/種子將返回） 收穫內容：該項目和數量範圍

這裏的JSON我設置（溫柔，我的n00b）：

{ 
"Pot": [ 
{"potType": "Clay", 
"Seed": [ 
    {"seedType": "Grain", 
    "HarvestBasket" : [ 
     {"harvestBasketID": 1, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Wheat", "min": 3, "max": 6}, 
      {"harvestItem": "Corn", "min": 1, "max": 3} 
      ] 
     }, 
     {"harvestBasketID": 2, "harvestBasketName": "temp", "chance": 50, 
     "harvestContent": [ 
      {"harvestItem": "Rice", "min": 10, "max": 12} 
      ] 
     }, 
     {"harvestBasketID": 3, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Corn", "min": 1, "max": 3}, 
      {"harvestItem": "Spelt", "min": 5, "max": 6} 
      ] 
     } 
    ] 
    }, 
    {"seedType": "Fruit", 
    "HarvestBasket" : [ 
     {"harvestBasketID": 1, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Apple", "min": 3, "max": 5}, 
      {"harvestItem": "Orange", "min": 1, "max": 3} 
      ] 
     }, 
     {"harvestBasketID": 2, "harvestBasketName": "temp", "chance": 50, 
     "harvestContent": [ 
      {"harvestItem": "Tangerine", "min": 10, "max": 12} 
      ] 
     }, 
     {"harvestBasketID": 3, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Kiwi", "min": 1, "max": 3}, 
      {"harvestItem": "Apple", "min": 5, "max": 6} 
      ] 
     } 
    ] 
    } 
] 
}, 

{"potType": "Brass",  
"Seed": [ 
    {"seedType": "Grain", 
    "HarvestBasket" : [ 
     {"harvestBasketID": 1, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Wheat", "min": 20, "max": 20}, 
      {"harvestItem": "Corn", "min": 20, "max": 20} 
      ] 
     }, 
     {"harvestBasketID": 2, "harvestBasketName": "temp", "chance": 50, 
     "harvestContent": [ 
      {"harvestItem": "Rice", "min": 20, "max": 20} 
      ] 
     }, 
     {"harvestBasketID": 3, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Corn", "min": 1, "max": 3}, 
      {"harvestItem": "Spelt", "min": 20, "max": 20} 
      ] 
     } 
    ] 
    }, 
    {"seedType": "Fruit", 
    "HarvestBasket" : [ 
     {"harvestBasketID": 1, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Apple", "min": 25, "max": 25}, 
      {"harvestItem": "Orange", "min": 25, "max": 25} 
      ] 
     }, 
     {"harvestBasketID": 2, "harvestBasketName": "temp", "chance": 50, 
     "harvestContent": [ 
      {"harvestItem": "Tangerine", "min": 25, "max": 25} 
      ] 
     }, 
     {"harvestBasketID": 3, "harvestBasketName": "temp", "chance": 25, 
     "harvestContent": [ 
      {"harvestItem": "Kiwi", "min": 25, "max": 25}, 
      {"harvestItem": "Apple", "min": 25, "max": 25} 
      ] 
     } 
    ] 
    } 
] 
} 

] 
} 

我有以下類別的設置。請注意，我已經手動爲這些類添加了值，並且現在正試圖讓JSON分配這些值，所以從理論上講，類設置應該很好。所以，我使用的是GSON，它似乎在讀取文件，但是當我輸出任何東西時，我得到了nullPointer異常。我不知道如果導入不工作或者是什麼......下面是我搞亂代碼：

class Response { 
Map<String, Pot> myPot; 

public Map<String, Pot> getPot() { 
    return myPot; 
} 
} 

    public static void JSONAssign() { 

    Gson gson = new Gson(); 
    BufferedReader br = null; 


    try { 
     br = new BufferedReader(new FileReader("/Users/patkhumprakob/Documents/workspace/Plants/src/harvestLoot.json")); 

     Response response; 
     try { 
      response = gson.fromJson(br, Response.class); 
      System.out.println(response.hashCode()); 
      System.out.println(response.toString()); 

      System.out.println(response.getPot().getClass()); 

控制檯響應我得到的是：

1717159510 
Response@6659c656 
Exception in thread "main" java.lang.NullPointerException 
at PlantsMain.JSONAssign(PlantsMain.java:56) 
at PlantsMain.main(PlantsMain.java:36) 

我試過其他比如傳遞給Get函數，但是我想如果我不能返回類的類型，我會遇到更大的問題。

Answer 1

定義這些類：

class Pots { 
    List<Pot> Pot; 
    } 

    class Pot { 
    protected String potType; 
    protected List<Seed> Seed; 
    } 

    class HarvestBasket { 
    protected String harvestBasketID; 
    protected String harvestBasketName; 
    protected int chance; 
    protected List<HarvestContent> harvestContent; 
    } 

    class HarvestContent { 
    protected String harvestItem; 
    protected int min; 
    protected int max; 
    } 

    class Seed { 
    protected String seedType; 
    protected List<HarvestBasket> HarvestBasket; 
    } 

然後使用：

Gson gson = new Gson(); 
Pots pots = gson.fromJson("Your JSON content", Pots.class); 

希望它能幫助。