Lorsque vous manipulez de grands objets ou traitez des données de manière incrémentielle, le téléchargement en flux continu vous permet de lire le contenu des objets depuis OSS par blocs. Cette approche évite de charger l'intégralité de l'objet en mémoire simultanément, améliorant ainsi l'efficacité et les performances. Elle convient particulièrement au téléchargement d'objets dépassant les limites de mémoire, au traitement des données en temps réel pour réduire l'empreinte mémoire, ainsi qu'aux scénarios où les données sont récupérées étape par étape via le réseau.
Notes d'utilisation
Cette rubrique utilise l'endpoint public de la région Chine (Hangzhou). Pour accéder à OSS depuis d'autres services Alibaba Cloud situés dans la même région, privilégiez un endpoint interne. Pour obtenir la liste des régions et endpoints pris en charge, consultez la page Régions et endpoints.
Les identifiants d'accès utilisés dans cette rubrique sont extraits des variables d'environnement. Pour plus de détails, reportez-vous à la section 配置访问凭证.
Nous illustrons ici la création d'une instance OSSClient à partir d'un endpoint OSS. Pour d'autres configurations, telles que l'utilisation d'un domaine personnalisé ou l'authentification via des identifiants du Security Token Service (STS), consultez la documentation relative à la Configuration du client.
L'utilisation du téléchargement en flux continu nécessite l'autorisation
oss:GetObject. Pour savoir comment attribuer cette permission, consultez la procédure d'Attribution d'une politique personnalisée.
Exemple de code
Le code suivant montre comment lire le contenu d'un objet OSS par blocs et le stocker dans un tableau d'octets.
import com.aliyun.oss.ClientBuilderConfiguration;
import com.aliyun.oss.OSS;
import com.aliyun.oss.common.auth.*;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.common.comm.SignVersion;
import com.aliyun.oss.model.*;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
public class Stream {
public static void main(String[] args) throws Exception {
// In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint. For more information about the endpoints of other regions, see Regions and endpoints.
String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.
EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
// Specify the name of the bucket. Example: examplebucket.
String bucketName = "examplebucket";
// Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path.
String objectName = "exampledir/exampleobject.txt";
// Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou.
String region = "cn-hangzhou";
// Create an OSSClient instance.
// Call the shutdown method to release resources when the OSSClient is no longer in use.
ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
OSS ossClient = OSSClientBuilder.create()
.endpoint(endpoint)
.credentialsProvider(credentialsProvider)
.clientConfiguration(clientBuilderConfiguration)
.region(region)
.build();
try {
// ossObject includes the bucket name, object name, object metadata, and an input stream.
OSSObject ossObject = ossClient.getObject(bucketName, objectName);
InputStream inputStream = ossObject.getObjectContent();
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
// Read the object content and store it in a byte array.
byte[] readBuffer = new byte[1024];
int bytesRead;
while ((bytesRead = inputStream.read(readBuffer)) != -1) {
byteArrayOutputStream.write(readBuffer, 0, bytesRead);
}
// Obtain the final result.
byte[] fileBytes = byteArrayOutputStream.toByteArray();
// Display the length of the byte array.
System.out.println("Downloaded file size: " + fileBytes.length + " bytes");
// You must close the obtained stream after the object is read. Otherwise, connection leaks may occur. Consequently, no connections are available and an exception occurs.
inputStream.close();
byteArrayOutputStream.close();
// If you do not close the ossObject object after it is used, connection leaks may occur. Consequently, no connections are available and an exception occurs.
ossObject.close();
} catch (OSSException oe) {
System.out.println("Caught an OSSException, which means your request made it to OSS, "
+ "but was rejected with an error response for some reason.");
System.out.println("Error Message:" + oe.getErrorMessage());
System.out.println("Error Code:" + oe.getErrorCode());
System.out.println("Request ID:" + oe.getRequestId());
System.out.println("Host ID:" + oe.getHostId());
} catch (Throwable ce) {
System.out.println("Caught an ClientException, which means the client encountered "
+ "a serious internal problem while trying to communicate with OSS, "
+ "such as not being able to access the network.");
System.out.println("Error Message:" + ce.getMessage());
} finally {
if (ossClient != null) {
ossClient.shutdown();
}
}
}
}L'exemple ci-dessous illustre le téléchargement des données d'un objet nommé exampleobject.txt depuis un flux vers un fichier local nommé examplefile.txt, situé dans le répertoire D:\localpath :
import com.aliyun.oss.ClientBuilderConfiguration;
import com.aliyun.oss.OSS;
import com.aliyun.oss.common.auth.*;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.common.comm.SignVersion;
import com.aliyun.oss.model.OSSObject;
import java.io.*;
public class GetObjectStreamtoLocalFile {
public static void main(String[] args) throws Exception {
// In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint. For more information about the endpoints of other regions, see Regions and endpoints.
String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
// Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured.
EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
// Specify the name of the bucket. Example: examplebucket.
String bucketName = "examplebucket";
// Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path.
String objectName = "exampledir/exampleobject.txt";
// Specify the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the region to cn-hangzhou.
String region = "cn-hangzhou";
// Specify the local path in which you want to store the files.
String localFilePath = "D:\\localpath\\examplefile.txt"; // Specify the path of the local file.
// Create an OSSClient instance.
// Call the shutdown method to release resources when the OSSClient is no longer in use.
ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
OSS ossClient = OSSClientBuilder.create()
.endpoint(endpoint)
.credentialsProvider(credentialsProvider)
.clientConfiguration(clientBuilderConfiguration)
.region(region)
.build();
try {
// Retrieve the object's input stream.
OSSObject ossObject = ossClient.getObject(bucketName, objectName);
InputStream inputStream = ossObject.getObjectContent();
// Create an output stream to the local file.
try (FileOutputStream fileOutputStream = new FileOutputStream(localFilePath)) {
byte[] buffer = new byte[1024];
int bytesRead;
// Read the content in chunks and write it to a local file.
while ((bytesRead = inputStream.read(buffer)) != -1) {
fileOutputStream.write(buffer, 0, bytesRead);
}
System.out.println("Downloaded file saved to: " + localFilePath);
}
// Close the input stream.
inputStream.close();
// Close ossObject.
ossObject.close();
} catch (OSSException oe) {
System.out.println("Caught an OSSException, which means your request made it to OSS, "
+ "but was rejected with an error response for some reason.");
System.out.println("Error Message:" + oe.getErrorMessage());
System.out.println("Error Code:" + oe.getErrorCode());
System.out.println("Request ID:" + oe.getRequestId());
System.out.println("Host ID:" + oe.getHostId());
} catch (Throwable ce) {
System.out.println("Caught an ClientException, which means the client encountered "
+ "a serious internal problem while trying to communicate with OSS, "
+ "such as not being able to access the network.");
System.out.println("Error Message:" + ce.getMessage());
} finally {
if (ossClient != null) {
ossClient.shutdown();
}
}
}
}