AWS DynamoDB RuntimeException

Question

Hey guys im trying to read some data from a table in DynamoDB in Android Studio and despite my arduous endeavors, I keep getting this exception. Any ideas how to fix it?

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

You create a second instance credentialsProvider which is hiding the class member. As result the used class member credentialsProvider is not initialized and null.

Remove CognitoCachingCredentialsProvider at the initialization line.

Edit: I'm not familar with android specials. But from a jav perspecptive it should loop like:

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

And the BackT class should contain a constructor:

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

and the DB initialization should use the local member:

new AmazonDynamoDBClient(localCredProvider);

Something that way you should try. Otherwise the credential provider returns a NULL value somewhere.