**文件管理**
##############################
在NOS中，用户可以通过一系列的接口管理桶(Bucket)中的文件(Object)，比如ListObjects，DeleteObject，CopyObject，DoesObjectExist等。

列出桶中的文件
=============================
您可以使用AmazonS3Client.ListObjects列出存储中间中的文件::
    
    public void ListObjects(string bucketName){            
        try
        {
            var keys = new List<string>();
            ListObjectsResponse result = null;
            string nextMarker = string.Empty;
            do
            {
                var listObjectsRequest = new ListObjectsRequest()
                {
                    BucketName = bucketName,
                    Marker = nextMarker,
                    MaxKeys = 5
                };
                result = s3Client.ListObjects(listObjectsRequest);

                foreach (var obj in result.S3Objects)
                {
                    Console.WriteLine(obj.Key);
                }

                nextMarker = result.NextMarker;
            } while (result.IsTruncated);

            Console.WriteLine("List objects of bucket:{0} succeeded ", bucketName);
        }
        catch (AmazonS3Exception ex)
        {
            Console.WriteLine("Failed with HTTPStatus: {0}; \nErrorCode: {1}; \nErrorMessage: {2}; \nRequestID:{3};",
                ex.StatusCode, ex.ErrorCode, ex.Message, ex.RequestId);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed with error info: {0}", ex.Message);
        }
    }
    

上述代码中的ListObjectsRequest中的可选参数如下所示:

+------------------------+-------------------------------------------------------------------------------------------------------------------------+
|参数                    |    说明                                                                                                                 |
+========================+=========================================================================================================================+
| Delimiter              |用于对Object名字进行分组的字符。所有名字包含指定的前缀且第一次出现delimiter字符之间的object作为一组元素。限制长度为10。  |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+
| Prefix                 |限定返回的object key必须以prefix作为前缀。注意使用prefix查询时，返回的key中仍会包含prefix                                |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+
| MaxKeys                |限定此次返回object的最大数，如果不设定，默认为100                                                                        |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+
| Marker                 |设定结果从marker之后按字母排序的第一个开始返回                                                                           |
+------------------------+-------------------------------------------------------------------------------------------------------------------------+

.. note::

	1. 上述表中的参数都是可选参数

判断文件是否存在
============================
您可以使用AmazonS3Client.GetObjectMetadata的返回值来判断文件是否存在::

    public bool DoesObjectExist(string bucketNaame,string key){
        try
        {
            var response = s3Client.GetObjectMetadata(new GetObjectMetadataRequest(){
                BucketName = bucketNaame,
                Key = key
            });

            return true;
        }
        catch (Amazon.S3.AmazonS3Exception ex)
        {
            if (ex.StatusCode == System.Net.HttpStatusCode.NotFound)
                return false;
        }
        return false;
    }

删除单个文件
===========================
您可以使用AmazonS3Client.DeleteObject删除单个需要删除的文件::

    public void DeleteObject(string bucketNaame, string key)
    {
        try
        {
            var resp = s3Client.DeleteObject(bucketNaame,key);
            Console.WriteLine("StatusCode : {0}", resp.HttpStatusCode);
        }
        catch (AmazonS3Exception ex)
        {
            Console.WriteLine("Failed with HTTPStatus: {0}; \nErrorCode: {1}; \nErrorMessage: {2}; \nRequestID:{3};",
                ex.StatusCode, ex.ErrorCode, ex.Message, ex.RequestId);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed with error info: {0}", ex.Message);
        }
    }


删除多个文件
============================
您可以使用AmazonS3Client.DeleteObjects批量删除文件::

    public void DeleteObjects(string bucket)
    {
        try
        {
            var keys = new List<KeyVersion>();
            var listObjectsResult = s3Client.ListObjects(bucket);
            foreach (var obj in listObjectsResult.S3Objects)
            {
                keys.Add(new KeyVersion(){
                    Key = obj.Key
                });
            }
            keys.Add(new KeyVersion()
            {
                Key = "NotExist" //不存在的key
            });
            var result = s3Client.DeleteObjects(new DeleteObjectsRequest(){
                BucketName = bucket,
                Objects = keys,
                Quiet=false
            });

            Console.WriteLine("Delete objects succeeded");

            
        }
        catch (DeleteObjectsException ex)
        {
            var resp = ex.Response;
            Console.WriteLine("No. of objects successfully deleted = {0}", resp.DeletedObjects.Count);
            Console.WriteLine("No. of objects failed to delete = {0}", resp.DeleteErrors.Count);
            foreach (DeleteError deleteError in resp.DeleteErrors)
            {
                Console.WriteLine("Error Object Key: {0}\t{1}\t{2}", deleteError.Key, deleteError.Code, deleteError.Message);
            }
            foreach (var deleteError in resp.DeletedObjects)
            {
                Console.WriteLine("Object Key: {0}", deleteError.Key);
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed with error info: {0}", ex.Message);
        }
    }
拷贝文件
===========================
您可以使用AmazonS3Client.CopyObject拷贝文件::

    public void CopyObject(string sourceBucket, string sourceKey, string targetBucket, string targetKey)
    {
        try
        {
            var request = new CopyObjectRequest(){
                SourceBucket = sourceBucket,
                SourceKey = sourceKey,
                DestinationBucket = targetBucket,
                DestinationKey = targetKey
            };
            s3Client.CopyObject(request);

            Console.WriteLine("Copy object succeeded");
        }
        catch (AmazonS3Exception ex)
        {
            Console.WriteLine("Failed with HTTPStatus: {0}; \nErrorCode: {1}; \nErrorMessage: {2}; \nRequestID:{3};",
                ex.StatusCode, ex.ErrorCode, ex.Message, ex.RequestId);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed with error info: {0}", ex.Message);
        }
    }

.. attention::

	1. 支持跨桶的文件copy


获取文件的文件元信息
==========================
您可以使用AmazonS3Client.GetObjectMetadata获取对象的元数据信息::

 
    public void GetObjectMetadata(string bucket, string key)
    {
        try
        {
            var objectMetadata = s3Client.GetObjectMetadata(bucket, key);
            Console.WriteLine("Get Object Metadata succeeded");
        }
        catch (AmazonS3Exception ex)
        {
            Console.WriteLine("Failed with HTTPStatus: {0}; \nErrorCode: {1}; \nErrorMessage: {2}; \nRequestID:{3};",
                ex.StatusCode, ex.ErrorCode, ex.Message, ex.RequestId);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed with error info: {0}", ex.Message);
        }
    }

生成私有对象可下载的URL链接
=============================
您可以使用AmazonS3Client.GetPreSignedURL获取对象的下载URL::

    public void GetObjectDownloadURL(string bucket, string key){
        try
        {
            GetPreSignedUrlRequest request1 = new GetPreSignedUrlRequest
            {
                BucketName = bucket,
                Key = key,
                Expires = DateTime.Now.AddMinutes(5) //根据实际需要设置过期时间
            };
            string urlString = s3Client.GetPreSignedURL(request1);
            Console.WriteLine(urlString);
        }
        catch (AmazonS3Exception ex)
        {
            Console.WriteLine("Failed with HTTPStatus: {0}; \nErrorCode: {1}; \nErrorMessage: {2}; \nRequestID:{3};",
                ex.StatusCode, ex.ErrorCode, ex.Message, ex.RequestId);
        }
        catch (Exception ex)
        {
            Console.WriteLine("Failed with error info: {0}", ex.Message);
        }
    }