Ao trabalhar com objetos grandes ou processar dados de forma incremental, use o download via streaming para ler o conteúdo do objeto no OSS em blocos. Essa abordagem evita carregar todo o objeto na memória de uma só vez, o que melhora a eficiência e o desempenho. Esse método é ideal para baixar objetos que excedem os limites de memória, processar dados em tempo real para reduzir o uso de memória e atender a cenários em que os dados são recuperados passo a passo pela rede.
Observações de uso
Este tópico usa o endpoint público da região China (Hangzhou). Para acessar o OSS a partir de outros serviços da Alibaba Cloud na mesma região, use um endpoint interno. Para obter detalhes sobre as regiões e endpoints compatíveis, consulte Regiões e endpoints.
Neste tópico, as credenciais de acesso são obtidas de variáveis de ambiente. Para mais informações, consulte Configurar credenciais de acesso.
Este tópico demonstra como criar uma instância OSSClient com um endpoint do OSS. Para configurações alternativas, como usar um domínio personalizado ou autenticar-se com credenciais do Security Token Service (STS), consulte Configuração do cliente.
Para usar o download via streaming, você precisa da permissão
oss:GetObject. Para mais informações, consulte Conceder uma política personalizada.
Código de exemplo
O código a seguir mostra como ler o conteúdo de um objeto do OSS em blocos e armazená-lo em um array 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();
}
}
}
}O código abaixo exemplifica como baixar os dados de um objeto chamado exampleobject.txt de um stream para um arquivo chamado examplefile.txt no diretório 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();
}
}
}
}