Downloading Objects

Last updated: 2020-08-26 11:01:35

    Overview

    This document provides an overview of APIs and SDK sample codes related to object download.

    API Operation Description
    GET Object Downloading an object Downloads an object to the local file system

    SDK API Reference

    For the parameters and method descriptions of all the APIs in the SDK, see SDK API Reference.

    Advanced APIs (recommended)

    Downloading an object

    The advanced version of the GET Object API uses more encapsulated logic to allow you to suspend, resume (via checkpoint restart), or cancel download requests.

    Sample code:

    // The advanced download API supports checkpoint restart. To do so, a `HEAD` request will be sent first to get file information before download.
    // If you are using a temporary key or accessing with a sub-account, please make sure that your access permission list includes HeadObject.
    
    // Initialize `TransferConfig`. The default configuration is used here. If you need to customize the configuration, please see the SDK API documentation.
    TransferConfig transferConfig = new TransferConfig.Builder().build();
    // Initialize TransferManager
    TransferManager transferManager = new TransferManager(cosXmlService,
            transferConfig);
    
    String bucket = "examplebucket-1250000000"; // Bucket in the format: `BucketName-APPID`
    String cosPath = "exampleobject"; // The location identifier of the object in the bucket, i.e. the object key
    // Local directory path
    String savePathDir = context.getExternalCacheDir().toString();
    // The file name saved locally. If not specified (null), it will be the same as the COS file name
    String savedFileName = "exampleobject";
    
    Context applicationContext = context.getApplicationContext(); // application
    // context
    COSXMLDownloadTask cosxmlDownloadTask =
            transferManager.download(applicationContext,
                    bucket, cosPath, savePathDir, savedFileName);
    
    // Set the download progress callback
    cosxmlDownloadTask.setCosXmlProgressListener(new CosXmlProgressListener() {
        @Override
        public void onProgress(long complete, long target) {
            // todo Do something to update progress...
        }
    });
    // Set the response callback
    cosxmlDownloadTask.setCosXmlResultListener(new CosXmlResultListener() {
        @Override
        public void onSuccess(CosXmlRequest request, CosXmlResult result) {
            COSXMLDownloadTask.COSXMLDownloadTaskResult downloadTaskResult =
                    (COSXMLDownloadTask.COSXMLDownloadTaskResult) result;
        }
    
        @Override
        public void onFail(CosXmlRequest request,
                           CosXmlClientException clientException,
                           CosXmlServiceException serviceException) {
            if (clientException != null) {
                clientException.printStackTrace();
            } else {
                serviceException.printStackTrace();
            }
        }
    });
    // Set the job status callback where you can view the job progress
    cosxmlDownloadTask.setTransferStateListener(new TransferStateListener() {
        @Override
        public void onStateChanged(TransferState state) {
            // todo notify transfer state
        }
    });

    Note:

    For more samples, please visit GitHub.

    Sample code 2: Suspending, resuming, or cancelling a download

    To suspend a download, use the code below:

    cosxmlDownloadTask.pause();;

    To resume a suspended download, use the code below:

    cosxmlDownloadTask.resume();

    To cancel a download, use the code below:

    cosxmlDownloadTask.cancel();

    Note:

    For more samples, please visit GitHub.

    Sample code 3: Downloading multiple objects

    // The location of the object in the bucket, i.e., the object key
    String[] cosPaths = new String[] {
            "exampleobject1",
            "exampleobject2",
            "exampleobject3",
    };
    
    for (String cosPath : cosPaths) {
    
        COSXMLDownloadTask cosxmlDownloadTask =
                transferManager.download(applicationContext,
                        bucket, cosPath, savePathDir, savedFileName);
        // Set the response callback
        cosxmlDownloadTask.setCosXmlResultListener(new CosXmlResultListener() {
            @Override
            public void onSuccess(CosXmlRequest request, CosXmlResult result) {
                COSXMLDownloadTask.COSXMLDownloadTaskResult cOSXMLDownloadTaskResult =
                        (COSXMLDownloadTask.COSXMLDownloadTaskResult) result;
            }
    
            @Override
            public void onFail(CosXmlRequest request,
                               CosXmlClientException clientException,
                               CosXmlServiceException serviceException) {
                if (clientException != null) {
                    clientException.printStackTrace();
                } else {
                    serviceException.printStackTrace();
                }
            }
        });
    }

    Note:

    For more samples, please visit GitHub.

    Simple Operations

    Downloading an object

    Description

    This API is used to download an object to the local file system.

    Sample code

    String bucket = "examplebucket-1250000000"; // Bucket name in the format: `BucketName-APPID`
    String cosPath = "exampleobject"; // The location identifier of the object in the bucket, i.e. the object key
    String savePath = context.getExternalCacheDir().toString(); // Local path
    
    GetObjectRequest getObjectRequest = new GetObjectRequest(bucket, cosPath,
            savePath);
    getObjectRequest.setProgressListener(new CosXmlProgressListener() {
        @Override
        public void onProgress(long progress, long max) {
            // todo Do something to update progress...
        }
    });
    
    cosXmlService.getObjectAsync(getObjectRequest, new CosXmlResultListener() {
        @Override
        public void onSuccess(CosXmlRequest cosXmlRequest,
                              CosXmlResult cosXmlResult) {
            GetObjectResult getObjectResult = (GetObjectResult) cosXmlResult;
        }
    
        @Override
        public void onFail(CosXmlRequest cosXmlRequest,
                           CosXmlClientException clientException,
                           CosXmlServiceException serviceException) {
            if (clientException != null) {
                clientException.printStackTrace();
            } else {
                serviceException.printStackTrace();
            }
        }
    });

    Note:

    For more samples, please visit GitHub.

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