java - Amazon Web Service DynamoDB 错误 com.amazonaws.auth.AWSCredentials

Question

所以我尝试将我的应用程序连接到亚马逊云 Nosql 服务器 DynamoDB，我一直在遵循他们的教程，但由于不断发生此错误，似乎无法使其工作:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.humber.industech.industechapp/com.humber.industech.industechapp.DataActivity}: 
java.lang.NullPointerException: Attempt to invoke interface method 'com.amazonaws.auth.AWSCredentials com.amazonaws.auth.AWSCredentialsProvider.getCredentials()' on a null object reference

任何有关使用 AWS 进行设置的帮助将不胜感激，非常感谢!

代码如下:

public class DataActivity extends AppCompatActivity {

    private TextView t;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_data);
        //setting custom font
        t = (TextView) findViewById(R.id.textView3);
        Typeface customFont = Typeface.createFromAsset(getAssets(),"fonts/Prezident.ttf");
        t.setTypeface(customFont);
        saveData();
    }

     public void saveData(){
        CognitoCachingCredentialsProvider credentialsProvider = CredentialProviderSingleton.getInstance(this);
        AmazonDynamoDBClient ddbClient = new AmazonDynamoDBClient(credentialsProvider);
        DynamoDBMapper mapper = new DynamoDBMapper(ddbClient);
        Book book = new Book();
        book.setTitle("Test");
        book.setAuthor("Charles Dickens");
        book.setPrice(1299);
        book.setIsbn("1235674");
        book.setHardCover(false);
        mapper.save(book);
    }
}



public class CredentialProviderSingleton {

    static CognitoCachingCredentialsProvider credentialProvider;

    public static CognitoCachingCredentialsProvider getInstance(Context context){
        if (credentialProvider == null){
            CognitoCachingCredentialsProvider credentialsProvider = new CognitoCachingCredentialsProvider(
                    context.getApplicationContext(),"POOL_ID", Regions.US_WEST_2);
        }
        return credentialProvider;
    }
}

Answer 1

该错误位于 CredentialsProviderSingleton 中

您创建一个凭证提供程序作为新变量

CognitoCachingCredentialsProvider凭据提供程序=新CognitoCachingCredentialsProvider( context.getApplicationContext(),"POOL_ID", Regions.US_WEST_2);

但是您返回类变量 credentialProvider (注意它在凭据末尾没有“s”)。该变量为 null，因为它从未被声明过。