Android - Error java.lang.UnsupportedOperationException：JsonNull

Question

我想在我的應用程序中使用JSON字符串，Retrofit和其他東西。但是在這個特定的模型中，我的JSON字符串是空的。

這是我反序列化我的字符串的方法：

public static class TaskGSON implements JsonSerializer<Task>, JsonDeserializer<Task>{ 

    @Override 
    public Task deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException { 
     System.out.println(json.toString()); 
     if (!json.isJsonNull()) { 
     final JsonObject jsonObject = json.getAsJsonObject(); 
     Task t = new Task(); 
     t.mId = jsonObject.get(NAMES.Server.ID).getAsString(); 
     t.mProjectId = jsonObject.get(NAMES.Server.PROJECT_ID).getAsString(); 
     t.mTitle = jsonObject.get(NAMES.Server.TITLE).getAsString(); 
     t.mPriority = Priority.deSerialize(jsonObject.get(NAMES.Server.PRIORITY).getAsString()); 
     t.mCreatedAt = context.deserialize(jsonObject.get(NAMES.Server.CREATED_AT), Date.class); 
     t.mCreatedById = jsonObject.get(NAMES.Server.CREATED_BY_ID).getAsString(); 
     t.mUpdatedAt = context.deserialize(jsonObject.get(NAMES.Server.UPDATED_AT), Date.class); 
     t.mFeedCount = jsonObject.get(NAMES.Server.FEED_COUNT).getAsInt(); 
     t.mPermissions = context.deserialize(jsonObject.get(NAMES.Server.PERMISSIONS), new TypeToken<List<Permission>>() {}.getType()); 

     if (jsonObject.has(NAMES.Server.COLLECTION_ID)) { 
      t.mCollectionId = jsonObject.get(NAMES.Server.COLLECTION_ID).getAsString(); 
     } 

     if (jsonObject.has(NAMES.Server.DESCRIPTION)) { 
      t.mDescription = jsonObject.get(NAMES.Server.DESCRIPTION).getAsString(); 
     } 
     if (jsonObject.has(NAMES.Server.DUE_DATE) && !jsonObject.get(NAMES.Server.DUE_DATE).isJsonNull()) { 
      t.mDueDate = context.deserialize(jsonObject.get(NAMES.Server.DUE_DATE), Date.class); 
     } 

     if (jsonObject.has(NAMES.Server.COMPLETED_AT)) { 
      t.mCompletedAt = context.deserialize(jsonObject.get(NAMES.Server.COMPLETED_AT), Date.class); 
     } 

     if (jsonObject.has(NAMES.Server.COMPLETED_BY_ID)) { 
      t.mCompletedById = jsonObject.get(NAMES.Server.COMPLETED_BY_ID).getAsString(); 
     } 

     if (jsonObject.has(NAMES.Server.DELETED_AT)) { 
      t.mDeletedAt = context.deserialize(jsonObject.get(NAMES.Server.DELETED_AT), Date.class); 
     } 

     if (jsonObject.has(NAMES.Server.COMPLETED)) { 
      t.mCompleted = jsonObject.get(NAMES.Server.COMPLETED).getAsBoolean(); 
     } 

     if (jsonObject.has(NAMES.Server.CHECKLIST)) { 
      t.mChecklists = context.deserialize(jsonObject.get(NAMES.Server.CHECKLIST), new TypeToken<List<Checklist>>() {}.getType()); 
     } 

     if (jsonObject.has(NAMES.Server.ATTACHMENTS)) { 
      t.mAttachments = context.deserialize(jsonObject.get(NAMES.Server.ATTACHMENTS), new TypeToken<List<Attachment>>() {}.getType()); 
     } 

     if (jsonObject.has(NAMES.Server.MARKERS)) { 
      t.mMarkers = context.deserialize(jsonObject.get(NAMES.Server.MARKERS), new TypeToken<List<Marker>>() {}.getType()); 
     } 
     if (jsonObject.has(NAMES.Server.CATEGORY_ID)) { 
     t.mCategory = jsonObject.get(NAMES.Server.CATEGORY_ID).getAsString(); 
     } 

     return t; 
     } else { 
     return null; 
     } 
    } 

那麼，問題是，當我評論的代碼，檢查是否有一個字段行「描述」和「的categoryId」在我JSON字符串我沒有收到錯誤，但是如果我取消註釋這些if語句，我會收到錯誤消息，說Json爲空。我不知道爲什麼。

這是完整的logcat：

09-22 17:02:57.890 21172-26613/com.construct.test E/AbstractEntitiesViewModel: Error 
                       java.lang.UnsupportedOperationException: JsonNull 
                        at com.google.gson.JsonElement.getAsString(JsonElement.java:191) 
                        at com.construct.v2.models.entities.task.Task$TaskGSON.deserialize(Task.java:740) 
                        at com.construct.v2.models.entities.task.Task$TaskGSON.deserialize(Task.java:717) 
                        at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69) 
                        at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41) 
                        at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) 
                        at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) 
                        at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:37) 
                        at retrofit2.converter.gson.GsonResponseBodyConverter.convert(GsonResponseBodyConverter.java:25) 
                        at retrofit2.ServiceMethod.toResponse(ServiceMethod.java:119) 
                        at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:218) 
                        at retrofit2.OkHttpCall.execute(OkHttpCall.java:180) 
                        at retrofit2.adapter.rxjava.CallExecuteOnSubscribe.call(CallExecuteOnSubscribe.java:40) 
                        at retrofit2.adapter.rxjava.CallExecuteOnSubscribe.call(CallExecuteOnSubscribe.java:24) 
                        at retrofit2.adapter.rxjava.BodyOnSubscribe.call(BodyOnSubscribe.java:36) 
                        at retrofit2.adapter.rxjava.BodyOnSubscribe.call(BodyOnSubscribe.java:28) 
                        at rx.Observable.unsafeSubscribe(Observable.java:10256) 
                        at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48) 
                        at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33) 
                        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) 
                        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) 
                        at rx.Observable.unsafeSubscribe(Observable.java:10256) 
                        at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:248) 
                        at rx.internal.operators.OperatorMerge$MergeSubscriber.onNext(OperatorMerge.java:148) 
                        at rx.internal.operators.OnSubscribeFromArray$FromArrayProducer.fastPath(OnSubscribeFromArray.java:76) 
                        at rx.internal.operators.OnSubscribeFromArray$FromArrayProducer.request(OnSubscribeFromArray.java:58) 
                        at rx.Subscriber.setProducer(Subscriber.java:211) 
                        at rx.internal.operators.OnSubscribeFromArray.call(OnSubscribeFromArray.java:32) 
                        at rx.internal.operators.OnSubscribeFromArray.call(OnSubscribeFromArray.java:24) 
                        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) 
                        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) 
                        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) 
                        at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) 
                        at rx.Observable.unsafeSubscribe(Observable.java:10256) 
                        at rx.internal.operators.OperatorSubscribeOn$SubscribeOnSubscriber.call(OperatorSubscribeOn.java:100) 
                        at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55) 
                        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:428) 
                        at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
                        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:272) 
                        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133) 
                        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607) 
                        at java.lang.Thread.run(Thread.java:761) 

兩個字段描述和類別可以爲空，但他們在我的Json存在。這很奇怪，因爲當我評論這些行時它工作得很好。

Answer 1

您應該從yourJsonObject.getAsString()更改爲yourJsonObject.toString()