如何使用google gson庫將帶有內部對象的json對象反序列化爲單個java對象？

Question

我有以下JSON文件：

{ 
    "sqldb": [ 
    { 
     "name": "mydb", 
     "label": "sqldb", 
     "plan": "sqldb_free", 
     "credentials": { 
     "port": 50000, 
     "db": "SQLDB", 
     "username": "xxxxxxx", 
     "host": "75.126.155.92", 
     "hostname": "75.126.155.92", 
     "jdbcurl": "jdbc:db2://75.126.155.92:50000/SQLDB", 
     "uri": "db2://xxxxxxx:xxxxxxx@75.126.155.92:50000/SQLDB", 
     "password": "xxxxxxx" 
     } 
    } 
    ] 
} 

的對象還具有以下結構：sqldb對象列表，其具有內部credentials對象。我怎樣才能將Google Gson library解析成單個的sqldb對象？我的意思是，可以通過使用GSON的註解，Java對象像下面創建：

public class VcapObject{ 
    private String name; 
    private String label; 
    private String plan; 
    private String port; 
    private String db; 
    private String username; 
    private String host; 
    private String hostname; 
    private String jdbcurl; 
    private String uri; 
    private String password; 
} 

將由填寫：

VcapObject vcapObject = gson.fromJson(vcapString, VcapObject.class); 

例如？

Answer 1

您可以創建包含VcapObject集合的包裝類，例如VcapList。然後，您可以將VcapList作爲類傳遞給fromJson。向VcapList添加一個方法，如果不是空的，則獲取第一個方法。

Answer 2

要擺脫內部credentials對象，您需要一個自定義JsonDeserializer，將內部類的字段複製到外部類。有幾種不同的策略可以採用，但是這裏是修改JSON樹並將其反饋給Gson的策略。

Gson gson = new GsonBuilder().registerTypeAdapter(VcapObject.class, new VcapDeserializer()).create(); 

注意事項 - -

public class VcapDeserializer implements JsonDeserializer<VcapObject> { 

    private static final String MERGE_FIELD = "credentials"; 
    final private Gson gson; 

    public VcapDeserializer() { 
     gson = new Gson(); 
    } 

    @Override 
    public VcapObject deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { 
     if(json.isJsonObject()) { 
      JsonObject jsonObject = json.getAsJsonObject(); 
      if(jsonObject.has(MERGE_FIELD)) { 
       // We have the object, get all the fields 
       JsonObject mergeObject = jsonObject.get(MERGE_FIELD).getAsJsonObject(); 
       Set<Map.Entry<String, JsonElement>> entries = mergeObject.entrySet(); 
       for(Map.Entry<String, JsonElement> entry : entries) { 
        // Copy property to top level object 
        jsonObject.add(entry.getKey(), entry.getValue()); 
       } 
       // now that we have copied the fields, remove the nested object 
       jsonObject.remove(MERGE_FIELD); 
      } 
      // Deserialize the top-level object 
      return gson.fromJson(jsonObject, VcapObject.class); 
     } else { 
      // top level is supposed to be an object 
      throw new IllegalStateException(); 
     } 
    } 
} 

然後用GsonBuilder創建自定義Gson例如從你的問題，如果你想擺脫頂級包裝對象的，目前尚不清楚。我假設不是因爲你沒有說數組總是要返回一個元素。所以，你仍然需要的是 -

public class SqlDbWrapper { 
    List<VcapObject> sqldb; 
} 

，然後用反序列化 -

SqlDbWrapper sqlDbWrapper = gson.fromJson(jsonString, SqlDbWrapper.class);