Cuando trabaje con objetos grandes o procese datos de forma incremental, utilice la descarga en streaming para leer el contenido de los objetos de OSS por fragmentos. De esta manera evita cargar todo el objeto en memoria al mismo tiempo y mejora la eficiencia y el rendimiento. Este método es adecuado para descargar objetos que superan los límites de memoria, procesar datos en tiempo real para reducir el consumo de memoria y recuperar información paso a paso a través de la red.
Notas de uso
En este tema se utiliza el endpoint público de la región China (Hangzhou). Para acceder a OSS desde otros servicios de Alibaba Cloud en la misma región, use un endpoint interno. Para más detalles sobre las regiones y los endpoints compatibles, consulte Regions and endpoints.
Las credenciales de acceso de este tema se obtienen de variables de entorno. Para más información, consulte 配置访问凭证.
Este tema muestra cómo crear una instancia de OSSClient con un endpoint de OSS. Para configuraciones alternativas, como usar un dominio personalizado o autenticarse con credenciales de Security Token Service (STS), consulte Client configuration.
Para usar la descarga en streaming, necesita el permiso
oss:GetObject. Para más información, consulte Grant a custom policy.
Código de ejemplo
A continuación se muestra un ejemplo de cómo leer el contenido de un objeto de OSS por fragmentos y almacenarlo en un arreglo de bytes.
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();
}
}
}
}El siguiente código de ejemplo descarga los datos del objeto llamado exampleobject.txt mediante streaming y los guarda como el archivo examplefile.txt en el directorio 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();
}
}
}
}