By default, if you upload an object that has the same name as an existing object, the existing object is overwritten by the uploaded object. This topic describes how to configure the x-oss-forbid-overwrite request header to prevent existing objects from being overwritten by objects with the same names when you copy objects or perform simple upload or multipart upload.
Usage notes
In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access Object Storage Service (OSS) by using other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about the regions and endpoints supported by OSS, see Regions, endpoints and open ports.
In this topic, access credentials are obtained from environment variables. For more information about how to configure access credentials, see Configure access credentials.
In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Create an OSSClient instance.
Prevent overwrites in a simple upload task
The following sample code provides an example on how to prevent existing objects from being overwritten by objects that have the same names when you perform simple upload:
import com.aliyun.oss.ClientException;
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.model.*;
import java.io.ByteArrayInputStream;
public class Demo {
public static void main(String[] args) throws Exception {
// In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint.
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. Do not include the bucket name in the full path.
String objectName = "exampledir/object";
String content = "Hello OSS!";
// 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.
ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
OSS ossClient = OSSClientBuilder.create()
.endpoint(endpoint)
.credentialsProvider(credentialsProvider)
.clientConfiguration(clientBuilderConfiguration)
.region(region)
.build();
try {
// Create a PutObjectRequest object.
PutObjectRequest putObjectRequest = new PutObjectRequest(bucketName, objectName, new ByteArrayInputStream(content.getBytes()));
// Specify whether to overwrite an existing object with the same name.
// By default, if x-oss-forbid-overwrite is not specified, an existing object with the same name is overwritten.
// If x-oss-forbid-overwrite is set to false, an existing object with the same name is overwritten.
// If x-oss-forbid-overwrite is set to true, an existing object with the same name is not overwritten. If an object with the same name already exists, an error is reported.
ObjectMetadata metadata = new ObjectMetadata();
metadata.setHeader("x-oss-forbid-overwrite", "true");
putObjectRequest.setMetadata(metadata);
// Upload the local file.
ossClient.putObject(putObjectRequest);
} 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 (ClientException 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();
}
}
}
}Prevent overwrites in an object copy task
Use CopyObjectRequest to copy a small object
The following sample code provides an example on how to prevent an existing object from being overwritten by a small object with the same name when you copy the small object by using CopyObjectRequest:
import com.aliyun.oss.ClientException; 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.model.*; public class Demo { public static void main(String[] args) throws Exception { // In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint. 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 source bucket. String sourceBucketName = "srcexamplebucket"; // Specify the full path of the source object. Do not include the bucket name in the full path. String sourceObjectName = "srcexampleobject.txt"; // Specify the name of the destination bucket. The destination bucket must be located in the same region as the source bucket. String destinationBucketName = "desexamplebucket"; // Specify the full path of the destination object. Do not include the bucket name in the full path. String destinationObjectName = "desexampleobject.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. ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration(); clientBuilderConfiguration.setSignatureVersion(SignVersion.V4); OSS ossClient = OSSClientBuilder.create() .endpoint(endpoint) .credentialsProvider(credentialsProvider) .clientConfiguration(clientBuilderConfiguration) .region(region) .build(); try { // Create a CopyObjectRequest object. CopyObjectRequest copyObjectRequest = new CopyObjectRequest(sourceBucketName, sourceObjectName, destinationBucketName, destinationObjectName); // Configure new metadata for the destination object. ObjectMetadata metadata = new ObjectMetadata(); metadata.setContentType("text/html"); // Specify whether to overwrite the existing object with the same name. // By default, if x-oss-forbid-overwrite is not specified, an existing object with the same name is overwritten. // If x-oss-forbid-overwrite is set to false, an existing object with the same name is overwritten. // If x-oss-forbid-overwrite is set to true, an existing object with the same name is not overwritten. If an object with the same name already exists, an error is reported. metadata.setHeader("x-oss-forbid-overwrite", "true"); copyObjectRequest.setNewObjectMetadata(metadata); // Copy the object. CopyObjectResult result = ossClient.copyObject(copyObjectRequest); System.out.println("ETag: " + result.getETag() + " LastModified: " + result.getLastModified()); } 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 (ClientException 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(); } } } }Copy a large object
The following sample code provides an example on how to prevent an existing object from being overwritten by a large object with the same name when you copy the large object by using multipart copy:
import com.aliyun.oss.ClientException; 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.model.*; import java.util.ArrayList; import java.util.List; public class Demo { public static void main(String[] args) throws Exception { // In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint. 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 source bucket. String sourceBucketName = "srcexamplebucket"; // Specify the full path of the source object. Do not include the bucket name in the full path. String sourceObjectName = "srcexampleobject.txt"; // Specify the name of the destination bucket. The destination bucket must be located in the same region as the source bucket. String destinationBucketName = "desexamplebucket"; // Specify the full path of the destination object. Do not include the bucket name in the full path. String destinationObjectName = "desexampleobject.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. ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration(); clientBuilderConfiguration.setSignatureVersion(SignVersion.V4); OSS ossClient = OSSClientBuilder.create() .endpoint(endpoint) .credentialsProvider(credentialsProvider) .clientConfiguration(clientBuilderConfiguration) .region(region) .build(); try { ObjectMetadata objectMetadata = ossClient.getObjectMetadata(sourceBucketName, sourceObjectName); // Query the size of the object that you want to copy. long contentLength = objectMetadata.getContentLength(); // Set the part size to 10 MB. long partSize = 1024 * 1024 * 10; // Calculate the total number of parts. int partCount = (int) (contentLength / partSize); if (contentLength % partSize != 0) { partCount++; } System.out.println("total part count:" + partCount); // Initialize a multipart copy task. You can specify the metadata of the destination object by using InitiateMultipartUploadRequest. InitiateMultipartUploadRequest initiateMultipartUploadRequest = new InitiateMultipartUploadRequest(destinationBucketName, destinationObjectName); // Specify whether to overwrite the existing object with the same name. // By default, if x-oss-forbid-overwrite is not specified, an existing object with the same name is overwritten. // If x-oss-forbid-overwrite is set to false, an existing object with the same name is overwritten. // If x-oss-forbid-overwrite is set to true, an existing object with the same name is not overwritten. If an object with the same name already exists, an error is reported. ObjectMetadata metadata = new ObjectMetadata(); metadata.setHeader("x-oss-forbid-overwrite", "true"); initiateMultipartUploadRequest.setObjectMetadata(metadata); InitiateMultipartUploadResult initiateMultipartUploadResult = ossClient.initiateMultipartUpload(initiateMultipartUploadRequest); String uploadId = initiateMultipartUploadResult.getUploadId(); // Start the multipart copy task. List<PartETag> partETags = new ArrayList<PartETag>(); for (int i = 0; i < partCount; i++) { // Calculate the size of each part. long skipBytes = partSize * i; long size = partSize < contentLength - skipBytes ? partSize : contentLength - skipBytes; // Create an UploadPartCopyRequest object. You can specify conditions by using UploadPartCopyRequest. UploadPartCopyRequest uploadPartCopyRequest = new UploadPartCopyRequest(sourceBucketName, sourceObjectName, destinationBucketName, destinationObjectName); uploadPartCopyRequest.setUploadId(uploadId); uploadPartCopyRequest.setPartSize(size); uploadPartCopyRequest.setBeginIndex(skipBytes); uploadPartCopyRequest.setPartNumber(i + 1); UploadPartCopyResult uploadPartCopyResult = ossClient.uploadPartCopy(uploadPartCopyRequest); // Store the returned PartETags in partETags. partETags.add(uploadPartCopyResult.getPartETag()); } // Complete the multipart copy task. CompleteMultipartUploadRequest completeMultipartUploadRequest = new CompleteMultipartUploadRequest( destinationBucketName, destinationObjectName, uploadId, partETags); // Specify whether to overwrite the existing object with the same name. // By default, if x-oss-forbid-overwrite is not specified, an existing object with the same name is overwritten. // If x-oss-forbid-overwrite is set to false, an existing object with the same name is overwritten. // If x-oss-forbid-overwrite is set to true, an existing object with the same name is not overwritten. If an object with the same name already exists, an error is reported. completeMultipartUploadRequest.addHeader("x-oss-forbid-overwrite", "true"); ossClient.completeMultipartUpload(completeMultipartUploadRequest); } 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 (ClientException 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(); } } } }
Prevent overwrites in a multipart upload task
The following sample code provides an example on how to prevent an existing object from being overwritten by an object with the same name when you use multipart upload to upload the object:
import com.aliyun.oss.ClientException;
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.model.*;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
public class Demo {
public static void main(String[] args) throws Exception {
// In this example, the endpoint of the China (Hangzhou) region is used. Specify your actual endpoint.
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. Do not include the bucket name in the full path.
String objectName = "exampledir/object";
// 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.
ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
OSS ossClient = OSSClientBuilder.create()
.endpoint(endpoint)
.credentialsProvider(credentialsProvider)
.clientConfiguration(clientBuilderConfiguration)
.region(region)
.build();
try {
// Create an InitiateMultipartUploadRequest object.
InitiateMultipartUploadRequest request = new InitiateMultipartUploadRequest(bucketName, objectName);
// Specify whether to overwrite the existing object with the same name.
// By default, if x-oss-forbid-overwrite is not specified, an existing object with the same name is overwritten.
// If x-oss-forbid-overwrite is set to false, an existing object with the same name is overwritten.
// If x-oss-forbid-overwrite is set to true, an existing object with the same name is not overwritten. If an object with the same name already exists, an error is reported.
ObjectMetadata metadata = new ObjectMetadata();
metadata.setHeader("x-oss-forbid-overwrite", "true");
request.setObjectMetadata(metadata);
// Initiate a multipart upload task.
InitiateMultipartUploadResult upresult = ossClient.initiateMultipartUpload(request);
// Obtain the upload ID. The upload ID is the unique identifier of the multipart upload task. You can initiate related requests based on the upload ID, such as canceling or querying the multipart upload task.
String uploadId = upresult.getUploadId();
// partETags is a set of PartETags. A PartETag consists of the part number and ETag of an uploaded part
List<PartETag> partETags = new ArrayList<PartETag>();
// Calculate the total number of parts.
final long partSize = 1 * 1024 * 1024L; // 1MB
final File sampleFile = new File("<localFile>");
long fileLength = sampleFile.length();
int partCount = (int) (fileLength / partSize);
if (fileLength % partSize != 0) {
partCount++;
}
// Upload all parts.
for (int i = 0; i < partCount; i++) {
long startPos = i * partSize;
long curPartSize = (i + 1 == partCount) ? (fileLength - startPos) : partSize;
InputStream instream = new FileInputStream(sampleFile);
// Skip the parts that are uploaded.
instream.skip(startPos);
UploadPartRequest uploadPartRequest = new UploadPartRequest();
uploadPartRequest.setBucketName(bucketName);
uploadPartRequest.setKey(objectName);
uploadPartRequest.setUploadId(uploadId);
uploadPartRequest.setInputStream(instream);
// Configure the size of each part. Each part except for the last part must be larger than 100 KB.
uploadPartRequest.setPartSize(curPartSize);
// Configure part numbers. Each part is configured with a part number. The value ranges from 1 to 10000. If you configure a number beyond the range, OSS returns the InvalidArgument error code.
uploadPartRequest.setPartNumber( i + 1);
// Parts are not necessarily uploaded in order and can be uploaded from different OSS clients. OSS sorts the parts based on the part numbers and combines the parts into a complete object.
UploadPartResult uploadPartResult = ossClient.uploadPart(uploadPartRequest);
// After you upload a part, the response includes a PartETag. The PartETag is stored in partETags.
partETags.add(uploadPartResult.getPartETag());
}
// Create a CompleteMultipartUploadRequest object.
// When you complete a multipart upload task, you must provide all valid PartETags. After OSS receives the PartETags, OSS verifies all parts one by one. After all parts are verified, OSS combines the parts into a complete object.
CompleteMultipartUploadRequest completeMultipartUploadRequest =
new CompleteMultipartUploadRequest(bucketName, objectName, uploadId, partETags);
// Specify whether to overwrite the existing object with the same name.
// By default, if x-oss-forbid-overwrite is not specified, an existing object with the same name is overwritten.
// If x-oss-forbid-overwrite is set to false, an existing object with the same name is overwritten.
// If x-oss-forbid-overwrite is set to true, an existing object with the same name is not overwritten. If an object with the same name already exists, an error is reported.
completeMultipartUploadRequest.addHeader("x-oss-forbid-overwrite", "true");
// Complete the multipart upload task.
CompleteMultipartUploadResult completeMultipartUploadResult = ossClient.completeMultipartUpload(completeMultipartUploadRequest);
} 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 (ClientException 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();
}
}
}
}References
For the complete sample code that is used to prevent existing objects from being overwritten by objects that have the same names in object upload scenarios, visit GitHub.
For more information about the API operation that you can call to perform simple upload, see PutObject.
For more information about the API operation that you can call to copy an object, see CopyObject.
For more information about the API operations that you can call to perform multipart upload, see InitiateMultipartUpload and CompleteMultipartUpload.