Download file from Amazon AWS private Bucket

Download file from AWS S3 private Bucket

Amazon is providing many of the APIs, all are used in different scenarios,

Here, our aim is to download file using Amazon API, for that amazon's AWS S3 from SDK is used.

Add below dependency in your app's gradle file

compile 'com.amazonaws:aws-android-sdk-s3:2.3.0'

below are the classes you need to import

import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.mobileconnectors.s3.transferutility.TransferListener;
import com.amazonaws.mobileconnectors.s3.transferutility.TransferObserver;
import com.amazonaws.mobileconnectors.s3.transferutility.TransferState;
import com.amazonaws.mobileconnectors.s3.transferutility.TransferType;
import com.amazonaws.mobileconnectors.s3.transferutility.TransferUtility;
import com.amazonaws.services.s3.AmazonS3Client;

Declare Below variables in your class

private static AmazonS3Client sS3Client;
private static AWSCredentials sCredentials;
private static TransferUtility sTransferUtility;
private static TransferObserver observer;
private static List<TransferObserver> observers;

Below are configuration for downloading file from aws s3 private bucket

Step 1 : Gets an instance of CognitoCachingCredentialsProvider.

private static AWSCredentials getCredentials(String accessKey, String secretKey) {
    if (sCredentials == null) {
        sCredentials = new BasicAWSCredentials(accessKey,secretKey);
    }
    return sCredentials;
}

Step 2 : Gets an instance of the TransferUtility

public static TransferUtility getTransferUtility(String accessKey, String secretKey, Context context) {
    if (sTransferUtility == null) {
        sTransferUtility = new TransferUtility(getS3Client(accessKey, secretKey),
                context);
    }
    return sTransferUtility;
}

Step 3 : Gets an instance of a S3 client which is constructed, returns A 
default S3 client.proxyHost
public static AmazonS3Client getS3Client(String accessKey, String secretKey) {
    if (sS3Client == null) {
        sS3Client = new AmazonS3Client(getCredentials(accessKey, secretKey));
        sS3Client.setEndpoint({YOUR_AWS_ENDPOINT});
    }
    return sS3Client;
}
Observer to Get List of downloads in progress or we can say Gets all relevant 
transfers from the Transfer Service
private static void initDataObserver() {
        // Uses TransferUtility to get all previous download records.        
        observers = sTransferUtility.getTransfersWithType(TransferType.DOWNLOAD);
        TransferListener listener = new DownloadListener();
        for (TransferObserver observer : observers) {
            HashMap<String, Object> map = new HashMap<String, Object>();
            fillMap(map, observer, false);
            observer.setTransferListener(listener);

        }
    }
Fills in the map with information in the observer so that it can be used for 
further processing
public static void fillMap(Map<String, Object> map, TransferObserver observer, boolean isChecked) {
        int progress = (int) ((double) observer.getBytesTransferred() * 100 / observer
                .getBytesTotal());
        map.put("id", observer.getId());
        map.put("checked", isChecked);
        map.put("fileName", observer.getAbsoluteFilePath());
        map.put("progress", progress);
        map.put("bytes",
                getBytesString(observer.getBytesTransferred()) + "/" + getBytesString(observer.getBytesTotal()));
        map.put("state", observer.getState());
        map.put("percentage", progress + "%");
}

public static String getBytesString(long bytes) {
        // Converts number of bytes into proper scale.
        String[] quantifiers = new String[] {"KB", "MB", "GB", "TB"};
        double speedNum = bytes;
        for (int i = 0;; i++) {
            if (i >= quantifiers.length) {
                return "";
            }
            speedNum /= 1024;
            if (speedNum < 512) {
                return String.format("%.2f", speedNum) + " " + quantifiers[i];
            }
        }
    }

A TransferListener class that can listen to a download task and be notified when the 
status changes.

There are basically 3 methods of it :
1. onError() : which represents error while downloading
2. onProgressChanged() : which represents how many bytes are downloaded from total 
   no. of bytes
3. onStateChanged() : which represents changed state of downloading, states can be 
   any of below :
   
 - TransferState.IN_PROGRESS
 - TransferState.COMPLETED
 - TransferState.CANCELED
 - TransferState.FAILED
 - TransferState.PART_COMPLETED
 - TransferState.PAUSED
 - TransferState.PENDING_CANCEL
 - TransferState.PENDING_NETWORK_DISCONNECT
 - TransferState.PENDING_PAUSE
 - TransferState.RESUMED_WAITING
 - TransferState.UNKNOWN
 - TransferState.WAITING
 - TransferState.WAITING_FOR_NETWORK
private static class DownloadListener implements TransferListener {
               
       @Override        
       public void onError(int id, Exception e) {
            Log.e("Download observer", "onError: " + id, e);
            if (observers != null) {
                for (TransferObserver observer : observers) {
                    if (id == observer.getId()) {
                        Log.e("path", observer.getAbsoluteFilePath());
                        Log.e("key", observer.getKey());
                        Log.e("status", observer.getState() + "");
                    }
                }
            }
        }

        @Override        
        public void onProgressChanged(int id, long bytesCurrent, long bytesTotal) {
            Log.d("Download observer", String.format("onProgressChanged: %d, total: %d, current: %d", id, bytesTotal, bytesCurrent));
        }

        @Override        
        public void onStateChanged(int id, TransferState state) {
            Log.d("Download observer", "onStateChanged: " + id + ", " + state);
            for (TransferObserver observer : observers) {
                if (id == observer.getId()) {
                    Log.e("path", observer.getAbsoluteFilePath());
                    Log.e("key status", observer.getKey() + " " + observer.getState());
                }
            }
        }
    }
Finally, After completing configuration & initializing observer, you can download 
file via below code lines :

public static void startDownload(Context context) {

         sTransferUtility = getTransferUtility({AWS_ACCESS_KEY_ID}, {AWS_SECRET_ACCESS_KEY}, context);
         initDataObserver();
         observer = sTransferUtility.download({AWS_BUCKET_NAME}, {YOUR_AWS_KEY}, {LOCAL_FILE_PATH});
}
You are Done!!