5. 文件下载¶

S3 C# SDK提供了丰富的文件下载接口，用户可以通过以下方式从NOS获取文件:

下载文件到内存
下载到本地文件
分段下载
条件下载

5.1. 下载文件到内存¶

以下源代码实现下载文件到内存中:

public void GetObject(string bucket,string key){
    GetObjectRequest request = new GetObjectRequest
    {
        BucketName = bucket,
        Key = key
    };
    try
    {
        using (GetObjectResponse response = s3Client.GetObject(request))
        {
            using (StreamReader reader = new StreamReader(response.ResponseStream))
            {
                string contents = reader.ReadToEnd();
                Console.WriteLine(" Object   - " + response.Key);
                Console.WriteLine(" Contents - " + contents);
            }
        }

    } 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);
    }

}

5.2. 下载文件到本地文件¶

以下源代码实现将NOS文件下载到本地文件:

public void GetObjectToFile(string bucket, string key, string filePath)
 {
     GetObjectRequest request = new GetObjectRequest
     {
         BucketName = bucket,
         Key = key,

     };
     try
     {
         using (GetObjectResponse response = s3Client.GetObject(request))
         {
             response.WriteResponseStreamToFile(filePath);
         }

     }
     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);
     }

 }

5.3. 指定范围下载¶

如果存储在NOS中的文件较大，并且您只需要其中的一部分内容，您可以使用范围下载，下载指定范围的数据，如果指定的下载范围为”0-100”，则返回结果为第0字节到第100字节的数据，返回的数据包含第100字节，即range=0-100，如果指定的范围无效则下载整个文件，以下源代码获取range=0-100字节的内容:

public void GetObjectToFileByRange(string bucket, string key, string filePath)
{
    GetObjectRequest request = new GetObjectRequest
    {
        BucketName = bucket,
        Key = key,
        ByteRange = new ByteRange(0,3)//根据业务需求，自行设置

    };
    try
    {
        using (GetObjectResponse response = s3Client.GetObject(request))
        {
            response.WriteResponseStreamToFile(filePath);
        }
    }
    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

下载内容也可以存储到文件中
注意下载的区间为闭区间

5.4. 条件下载¶

下载文件时，可以指定限定条件，满足限定条件时下载，不满足时报错，不下载文件。可以使用的限定条件如下：

参数	说明	GetObjectRequest对应值
If-Modified-Since	如果指定的时间早于实际修改时间，则正常传送。否则返回错误	GetObjectRequest.IfModifiedSince

代码示例如下:

public void GetObjectToFileByModifiedSince(string bucket, string key, string filePath,DateTime dateTime)
{
    GetObjectRequest request = new GetObjectRequest
    {
        BucketName = bucket,
        Key = key,
        ModifiedSinceDate = dateTime
    };
    try
    {
        using (GetObjectResponse response = s3Client.GetObject(request))
        {
            response.WriteResponseStreamToFile(filePath);
        }

    }
    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);
    }

}