在阅读了书籍和在线文章中的SOLID代码之后，我想重构一个现有的类，以便它可以与'SOLID'兼容。
但是我觉得我迷路了，尤其是依赖注入：当我想实例化类的对象时，我需要'注入'所有依赖项，但依赖项本身有依赖项..这就是我的地方开始迷路了。
这个想法是这样的：我想创建一个类（在我的例子中，一个简单的Amazon S3包装器类）来简单上传＆amp;获取网址操作。
如何正确使用接口和依赖注入？什么地方出了错？ 班级应该怎么样？
这是我的代码：
public interface IConfigurationProvider
{
string GetConfigurationValue(String configurationKey);
}
public interface ILogger
{
void WriteLog(String message);
}
public interface IAWSClientProvider
{
AmazonS3Client GetAmazonS3Client();
}
public interface IAWSBucketManager
{
string GetDefaultBucketName();
}
public class AWSBucketManager : IAWSBucketManager
{
ILogger logger;
IConfigurationProvider configurationProvider;
public AWSBucketManager(ILogger Logger, IConfigurationProvider ConfigurationProvider)
{
logger = Logger;
configurationProvider = ConfigurationProvider;
}
public string GetDefaultBucketName()
{
string bucketName = string.Empty;
try
{
bucketName = configurationProvider.GetConfigurationValue("Amazon_S3_ExportAds_BucketName");
}
catch (Exception ex)
{
logger.WriteLog(String.Format("getBucketName : Unable to get bucket name from configuration.\r\n{0}", ex));
}
return bucketName;
}
}
public class AWSClientProvider : IAWSClientProvider
{
IConfigurationProvider configurationProvider;
IAWSBucketManager awsBucketManager;
ILogger logger;
private string awsS3BucketName;
private Dictionary<string, RegionEndpoint> regionEndpoints;
public AWSClientProvider(IConfigurationProvider ConfigurationProvider, IAWSBucketManager BucketManager, ILogger Logger)
{
logger = Logger;
configurationProvider = ConfigurationProvider;
awsBucketManager = BucketManager;
}
private RegionEndpoint getAWSRegion()
{
RegionEndpoint regionEndpoint = null;
// Init endpoints dictionary
try
{
IEnumerable<RegionEndpoint> regions = RegionEndpoint.EnumerableAllRegions;
regionEndpoints = regions.ToDictionary(r => r.SystemName, r => r);
}
catch (Exception Ex)
{
logger.WriteLog(String.Format("getAWSRegion() - Failed to get region list from AWS.\r\n{0}", Ex));
throw;
}
// Get configuration value
try
{
string Config = configurationProvider.GetConfigurationValue("Amazon_S3_Region");
if (String.IsNullOrEmpty(Config))
{
throw new Exception("getAWSRegion() : Amazon_S3_Region must not be null or empty string.");
}
regionEndpoint = regionEndpoints[Config];
}
catch (Exception Ex)
{
logger.WriteLog(String.Format("getAWSRegion() : Unable to get region settings from configuration.\r\n{0}", Ex));
throw Ex;
}
return regionEndpoint;
}
private AWSCredentials getAWSCredentials()
{
string accessKey, secretKey;
BasicAWSCredentials awsCredentials;
try
{
accessKey = configurationProvider.GetConfigurationValue("Amazon_S3_AccessKey");
secretKey = configurationProvider.GetConfigurationValue("Amazon_S3_SecretKey");
}
catch (Exception Ex)
{
logger.WriteLog(String.Format("getAWSCredentials() - Unable to get access key and secrey key values from configuration.\r\n", Ex.Message));
throw;
}
try
{
awsCredentials = new BasicAWSCredentials(accessKey, secretKey);
}
catch (Exception Ex)
{
logger.WriteLog(String.Format("getAWSCredentials() - Unable to create basic AWS credentials object.\r\n{0}", Ex.Message));
awsCredentials = null;
throw;
}
return awsCredentials;
}
public AmazonS3Client GetAmazonS3Client()
{
AmazonS3Client client = null;
RegionEndpoint region = getAWSRegion();
AWSCredentials credentials = getAWSCredentials();
awsS3BucketName = awsBucketManager.GetDefaultBucketName();
if (credentials != null)
{
client = new AmazonS3Client(credentials, region);
}
return client;
}
}
public class AWSS3Actions
{
IConfigurationProvider configurationProvider; // decoupling getting configuration
ILogger logger; // decoupling logger
IAWSClientProvider awsClientProvider;
private const int defaultExpirationDays = 14;
public AWSS3Actions(IConfigurationProvider ConfigurationProvider, ILogger Logger, IAWSClientProvider ClientProvider)
{
configurationProvider = ConfigurationProvider;
logger = Logger;
awsClientProvider = ClientProvider;
}
#region Private Mmethods
private string getFileUrl(string fileName, int expirationDaysPeriod, string awsS3BucketName)
{
GetPreSignedUrlRequest request = new GetPreSignedUrlRequest();
string URL = "";
DateTime dtBase = new DateTime();
dtBase = DateTime.Now;
dtBase = dtBase.AddDays(expirationDaysPeriod);
request.BucketName = awsS3BucketName;
request.Key = fileName;
request.Expires = dtBase;
try
{
URL = awsClientProvider.GetAmazonS3Client().GetPreSignedURL(request);
}
catch (AmazonS3Exception ex)
{
// log
logger.WriteLog(String.Format("getFileUrl() : Could not get presigned URL for the provided request.\r\n{0}", ex));
throw ex;
}
return URL;
}
private int getDefaultURLExpiration()
{
int expirationDays = 0;
try
{
// set the time span in days
int.TryParse(configurationProvider.GetConfigurationValue("getDefaultURLExpiration() : Amazon_S3_ExportAds_ExpirationDaysOfURL"), out expirationDays); // get from configuration util
}
catch
{
// in case of exception, set the min 14 days time space exiration
expirationDays = defaultExpirationDays;
}
return expirationDays;
}
private void validateUpload(string fileName, Stream fileStream)
{
if (fileName == null || fileName.Equals(string.Empty) || fileStream.Length < 1)
{
throw new Exception("fileName : File name must not be an empty string.");
}
if (fileStream == null)
{
throw new Exception("fileStream : Input memory stream (file stream) must not be null.");
}
}
#endregion
#region Public methods
public bool IsFileExists(string fileName, string awsS3BucketName)
{
bool fileExists = false;
try
{
S3FileInfo fileInfo = new S3FileInfo(awsClientProvider.GetAmazonS3Client(), awsS3BucketName, fileName);
fileExists = fileInfo.Exists;
}
catch (AmazonS3Exception Ex)
{
// log
logger.WriteLog(String.Format("isFileExists() : Could not determine if file (key) exists in S3 Bucket.\r\n", Ex.Message));
throw;
}
return fileExists;
}
public bool UploadObject(string fileName, Stream fileStream, string awsS3BucketName)
{
bool uploadResult = true;
// Validate input parameters
validateUpload(fileName, fileStream);
if (awsClientProvider.GetAmazonS3Client() != null)
{
try
{
PutObjectRequest request = new PutObjectRequest
{
BucketName = awsS3BucketName,
Key = fileName,
InputStream = fileStream
};
PutObjectResponse response = awsClientProvider.GetAmazonS3Client().PutObject(request);
if (response != null)
{
if (response.HttpStatusCode != System.Net.HttpStatusCode.OK)
{
var meta = response.ResponseMetadata.Metadata.Keys.
Select(k => k.ToString() + " : " + response.ResponseMetadata.Metadata[k]).
ToList().Aggregate((current, next) => current + "\r\n" + next);
// log error
logger.WriteLog(String.Format("Status Code: {0}\r\nETag : {1}\r\nResponse metadata : {1}",
(int)response.HttpStatusCode, response.ETag, meta));
// set the return value
uploadResult = false;
}
}
}
catch (AmazonS3Exception ex)
{
uploadResult = false;
if (ex.ErrorCode != null && (ex.ErrorCode.Equals("InvalidAccessKeyId") || ex.ErrorCode.Equals("InvalidSecurity")))
{
// LOG
logger.WriteLog(String.Format("UploadObject() : invalied credentials"));
throw ex;
}
else
{
// LOG
logger.WriteLog(String.Format("UploadObject() : Error occurred. Message:'{0}' when writing an object", ex.Message));
throw ex;
}
}
}
else
{
throw new Exception("UploadObject() : Could not start object upload because Amazon client is null.");
}
return uploadResult;
}
public bool UploadObject(string subFolderInBucket, string FileName, Stream fileStream, string awsS3BucketName)
{
return UploadObject(subFolderInBucket + @"/" + FileName, fileStream, awsS3BucketName);
}
public string GetURL(string fileName, string bucket)
{
string url = string.Empty;
try
{
if (IsFileExists(fileName, bucket))
{
url = getFileUrl(fileName, getDefaultURLExpiration(), bucket);
}
}
catch (Exception Ex)
{
// log
logger.WriteLog(String.Format("getURL : Failed in isFileExists() method. \r\n{0}", Ex.Message));
}
return url;
}
#endregion
}
答案 0 :(得分：3)
使用您当前的类结构，Composition Root可能如下所示：
var logger = new FileLogger("c:\\temp\\log.txt");
var configurationProvider = new ConfigurationProvider();
var actions = new AWSS3Actions(
configurationProvider,
logger,
new AWSClientProvider(
configurationProvider,
new AWSBucketManagerlogger(
logger,
configurationProvider),
logger));
上面的例子显示了一个手工对象图（a.k.a。Pure DI）。我的建议是首先应用Pure DI并切换到DI库（例如Simple Injector，Autofac或StructureMap），当手工构建对象图变得麻烦且维护繁重时。
从依赖注入的角度来看，尽管您的代码闻起来，但您正在做的事情看起来很明智。以下是一些参考资料：
旁注：通常，最好先预先加载配置值（在应用程序启动时），而不是在运行时读取它。在运行时读取这些值会导致以延迟方式读取这些值，从而防止应用程序快速失败，并在整个应用程序中扩展配置抽象的使用。如果可能，将这些原始配置值直接注入需要该值的类型的构造函数中。