AWS DynamoDB RuntimeException

Question

皆さん、Android StudioのDynamoDBのテーブルからデータを読み込もうとしていますが、私の手間がかかりましたが、この例外が発生しています。どのようにそれを修正するための任意のアイデア？

04-06 19:25:11.688 23407-23423/com.example.ali.dynamodb E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1 
Process: com.example.ali.dynamodb, PID: 23407 
java.lang.RuntimeException: An error occurred while executing doInBackground() 
at android.os.AsyncTask$3.done(AsyncTask.java:309) 
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354) 
at java.util.concurrent.FutureTask.setException(FutureTask.java:223) 
at java.util.concurrent.FutureTask.run(FutureTask.java:242) 
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
at java.lang.Thread.run(Thread.java:818) 
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'com.amazonaws.auth.AWSCredentials com.amazonaws.auth.AWSCredentialsProvider.getCredentials()' on a null object reference 
at com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient.invoke(AmazonDynamoDBClient.java:3504) 
at com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient.getItem(AmazonDynamoDBClient.java:929) 
at com.amazonaws.mobileconnectors.dynamodbv2.dynamodbmapper.DynamoDBMapper.load(DynamoDBMapper.java:393) 
at com.amazonaws.mobileconnectors.dynamodbv2.dynamodbmapper.DynamoDBMapper.load(DynamoDBMapper.java:466) 
at com.amazonaws.mobileconnectors.dynamodbv2.dynamodbmapper.DynamoDBMapper.load(DynamoDBMapper.java:340) 
at com.example.ali.dynamodb.MainActivity$BackT.doInBackground(MainActivity.java:172) 
at com.example.ali.dynamodb.MainActivity$BackT.doInBackground(MainActivity.java:161) 
at android.os.AsyncTask$2.call(AsyncTask.java:295) 
at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)  
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)  
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)  
at java.lang.Thread.run(Thread.java:818) 

MainActivity.java：

public class MainActivity extends AppCompatActivity { 
     private CognitoCachingCredentialsProvider credentialsProvider; 


     @Override 
     protected void onCreate(Bundle savedInstanceState) { 
       super.onCreate(savedInstanceState); 
       setContentView(R.layout.activity_main); 
       Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
       setSupportActionBar(toolbar); 

       String forumName = "Amazon DynamoDB"; 
       String threadSubject = "DynamoDB Thread 1"; 

       FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
       fab.setOnClickListener(new View.OnClickListener() { 
         @Override 
         public void onClick(View view) { 
           Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG) 
               .setAction("Action", null).show(); 
         } 
       }); 

       // Initialize the Amazon Cognito credentials provider 
       CognitoCachingCredentialsProvider credentialsProvider = new CognitoCachingCredentialsProvider(
           getApplicationContext(), 
           "eu-west-1:c9e997aa-5f3e-4c0a-b3d9-f6faf2a39ab7", // Identity Pool ID 
           Regions.EU_WEST_1 // Region 
       ); 


       new BackT().execute(""); 
     } 

     @Override 
     public boolean onCreateOptionsMenu(Menu menu) { 
       // Inflate the menu; this adds items to the action bar if it is present. 
       getMenuInflater().inflate(R.menu.menu_main, menu); 
       return true; 
     } 

     private static void GetUserName(DynamoDBMapper mapper, int id) throws Exception { 
       UserTable userTable = mapper.load(UserTable.class, id); 
     } 


     @Override 
     public boolean onOptionsItemSelected(MenuItem item) { 
       // Handle action bar item clicks here. The action bar will 
       // automatically handle clicks on the Home/Up button, so long 
       // as you specify a parent activity in AndroidManifest.xml. 
       int id = item.getItemId(); 

       //noinspection SimplifiableIfStatement 
       if (id == R.id.action_settings) { 
         return true; 
       } 

       return super.onOptionsItemSelected(item); 
     } 


     private class BackT extends AsyncTask<String, Void, String> { 
       @Override 
       protected String doInBackground(String... params) { 
         AmazonDynamoDBClient ddbClient = new AmazonDynamoDBClient(credentialsProvider); 

         TextView sample1 = (TextView) findViewById(R.id.sample1); 
         TextView sample2 = (TextView) findViewById(R.id.sample2); 
         TextView sample3 = (TextView) findViewById(R.id.sample3); 

         // Getting items from the row specified with primary key 
         DynamoDBMapper mapper = new DynamoDBMapper(ddbClient); 
         UserTable userTable = mapper.load(UserTable.class, 1); 
         String result1 = userTable.getFirstName(); 
         String result2 = userTable.getSurname(); 
         String result3 = userTable.getUserName(); 

         sample1.setText(result1); 
         sample2.setText(result2); 
         sample3.setText(result3); 

         mapper.save(userTable); 
         return "Executed"; 
       } 

       @Override 
       protected void onPostExecute(String result) { 
       } 

       @Override 
       protected void onPreExecute() { 
       } 

       @Override 
       protected void onProgressUpdate(Void... values) { 
       } 
     } 
} 

UserTable.java：

@DynamoDBTable(tableName = "USER_TABLE") 
public class UserTable { 
     private String dateOfBirth; 
     private String emailAddress; 
     private String FirstN; 
     private String SurN; 
     private String User_Acc_ID; 
     private String User_Address_ID; 
     private int User_ID; 
     private String User_Name; 

     @DynamoDBAttribute(attributeName = "DATE_OF_BIRTH") 
     public String getDOB() { 
       return dateOfBirth; 
     } 

     @DynamoDBAttribute(attributeName = "EMAIL_ADDRESS") 
     public String getEmailAddress() { 
       return emailAddress; 
     } 

     @DynamoDBAttribute(attributeName = "FIRST_NAME") 
     public String getFirstName() { 
       return FirstN; 
     } 

     @DynamoDBAttribute(attributeName = "SURNAME") 
     public String getSurname() { 
       return SurN; 
     } 

     @DynamoDBAttribute(attributeName = "USER_ACC_ID") 
     public String getUser_Acc_ID() { 
       return User_Acc_ID; 
     } 

     @DynamoDBAttribute(attributeName = "USER_ADDRESS_ID") 
     public String getUser_Address_ID() { 
       return User_Address_ID; 
     } 

     @DynamoDBHashKey(attributeName = "USER_ID") 
     public int getUserID() { 
       return User_ID; 
     } 

     public void setUserID(int user_id){ 
       this.User_ID = User_ID; 
     } 


     @DynamoDBAttribute(attributeName = "USER_ID") 
     public String getUserName() { 
       return User_Name; 
     } 

} 

Answer 1

あなたはクラスのメンバを隠している番目のインスタンスcredentialsProviderを作成します。その結果、使用されたクラスメンバcredentialsProviderは初期化されておらず、nullです。

初期化行でCognitoCachingCredentialsProviderを削除します。

編集： 私はアンドロイドスペシャルとは思えません。

new BackT(credentialsProvider).execute(""); 

そしてBackTクラスがコンストラクタ含まれている必要があります：

private AWSCredentialsProvider localCredProvider = null; 
public BackT(AWSCredentialsProvider credProvider) 
{ 
    if (null != credProvider) 
    { 
    this.localCredProvider = credProvider; 
    } 
    else 
    { 
     // add some error logging here 
    } 
} 

をし、DBの初期化は、ローカルメンバーを使用する必要があります。

new AmazonDynamoDBClient(localCredProvider); 

しかしJAVから、それはのようなループすべきperspecptiveあなたが試してみるようなやり方。それ以外の場合、資格プロバイダはNULL値をどこかに返します。