默认情况下,如果新添加文件与现有文件(Object)同名且对该文件有访问权限,则新添加的文件将覆盖原有的文件。本文介绍如何通过设置请求头x-oss-forbid-overwrite在简单上传、拷贝文件及分片上传等场景中禁止覆盖同名文件。

简单上传

以下代码用于简单上传时禁止覆盖同名文件:

import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSS;
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 {
        // Endpoint以华东1(杭州)为例,其它Region请按实际情况填写。
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // 阿里云账号AccessKey拥有所有API的访问权限,风险很高。强烈建议您创建并使用RAM用户进行API访问或日常运维,请登录RAM控制台创建RAM用户。
        String accessKeyId = "yourAccessKeyId";
        String accessKeySecret = "yourAccessKeySecret";
        // 填写Bucket名称,例如examplebucket。
        String bucketName = "examplebucket";
        // 填写Object的完整路径。Object完整路径中不能包含Bucket名称。
        String objectName = "exampledir/object";
        String content = "Hello OSS!";

        // 创建OSSClient实例。
        OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);

        try {
            // 创建PutObjectRequest对象。
            PutObjectRequest putObjectRequest = new PutObjectRequest(bucketName, objectName, new ByteArrayInputStream(content.getBytes()));

            // 指定上传文件操作时是否覆盖同名Object。
            // 不指定x-oss-forbid-overwrite时,默认覆盖同名Object。
            // 指定x-oss-forbid-overwrite为false时,表示允许覆盖同名Object。
            // 指定x-oss-forbid-overwrite为true时,表示禁止覆盖同名Object,如果同名Object已存在,程序将报错。
            ObjectMetadata metadata = new ObjectMetadata();
            metadata.setHeader("x-oss-forbid-overwrite", "true");
            putObjectRequest.setMetadata(metadata);

            // 上传文件。
            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();
            }
        }
    }
}

拷贝文件

  • 通过CopyObjectRequest拷贝

    以下代码用于通过CopyObjectRequest拷贝小文件时禁止覆盖同名文件:

    import com.aliyun.oss.ClientException;
    import com.aliyun.oss.OSS;
    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 {
            // Endpoint以华东1(杭州)为例,其它Region请按实际情况填写。
            String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // 阿里云账号AccessKey拥有所有API的访问权限,风险很高。强烈建议您创建并使用RAM用户进行API访问或日常运维,请登录RAM控制台创建RAM用户。
            String accessKeyId = "yourAccessKeyId";
            String accessKeySecret = "yourAccessKeySecret";
            // 填写源Bucket名称。
            String sourceBucketName = "srcexamplebucket";
            // 填写源Object的完整路径,完整路径中不能包含Bucket名称。
            String sourceObjectName = "srcexampleobject.txt";
            // 填写与源Bucket处于同一地域的目标Bucket名称。
            String destinationBucketName = "desexamplebucket";
            // 填写目标Object的完整路径。Object完整路径中不能包含Bucket名称。
            String destinationObjectName = "desexampleobject.txt";
    
            // 创建OSSClient实例。
            OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);
    
            try {
                // 创建CopyObjectRequest对象。
                CopyObjectRequest copyObjectRequest = new CopyObjectRequest(sourceBucketName, sourceObjectName, destinationBucketName, destinationObjectName);
    
                // 设置新的文件元信息。
                ObjectMetadata metadata = new ObjectMetadata();
                metadata.setContentType("text/html");
                // 指定拷贝文件操作时是否覆盖同名Object。
                // 不指定x-oss-forbid-overwrite时,默认覆盖同名Object
                // 指定x-oss-forbid-overwrite为false时,表示允许覆盖同名Object。
                // 指定x-oss-forbid-overwrite为true时,表示禁止覆盖同名Object,如果同名Object已存在,程序将报错。
                metadata.setHeader("x-oss-forbid-overwrite", "true");
                copyObjectRequest.setNewObjectMetadata(metadata);
    
                // 拷贝文件。
                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();
                }
            }
        }
    }
  • 拷贝大文件

    以下代码用于拷贝大文件(分片拷贝)时禁止覆盖同名文件:

    import com.aliyun.oss.ClientException;
    import com.aliyun.oss.OSS;
    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 {
            // Endpoint以华东1(杭州)为例,其它Region请按实际情况填写。
            String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
            // 阿里云账号AccessKey拥有所有API的访问权限,风险很高。强烈建议您创建并使用RAM用户进行API访问或日常运维,请登录RAM控制台创建RAM用户。
            String accessKeyId = "yourAccessKeyId";
            String accessKeySecret = "yourAccessKeySecret";
            // 填写源Bucket名称。
            String sourceBucketName = "srcexamplebucket";
            // 填写源Object的完整路径,完整路径中不能包含Bucket名称。
            String sourceObjectName = "srcexampleobject.txt";
            // 填写与源Bucket处于同一地域的目标Bucket名称。
            String destinationBucketName = "desexamplebucket";
            // 填写目标Object的完整路径。Object完整路径中不能包含Bucket名称。
            String destinationObjectName = "desexampleobject.txt";
    
            // 创建OSSClient实例。
            OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);
    
            try {
                ObjectMetadata objectMetadata = ossClient.getObjectMetadata(sourceBucketName, sourceObjectName);
                // 获取被拷贝文件的大小。
                long contentLength = objectMetadata.getContentLength();
    
                // 设置分片大小为10MB。
                long partSize = 1024 * 1024 * 10;
    
                // 计算分片总数。
                int partCount = (int) (contentLength / partSize);
                if (contentLength % partSize != 0) {
                    partCount++;
                }
                System.out.println("total part count:" + partCount);
    
                // 初始化拷贝任务。可以通过InitiateMultipartUploadRequest指定目标文件元信息。
                InitiateMultipartUploadRequest initiateMultipartUploadRequest = new InitiateMultipartUploadRequest(destinationBucketName, destinationObjectName);
                // 指定拷贝文件操作时是否覆盖同名Object。
                // 不指定x-oss-forbid-overwrite时,默认覆盖同名Object。
                // 指定x-oss-forbid-overwrite为false时,表示允许覆盖同名Object。
                // 指定x-oss-forbid-overwrite为true时,表示禁止覆盖同名Object,如果同名Object已存在,程序将报错。
                ObjectMetadata metadata = new ObjectMetadata();
                metadata.setHeader("x-oss-forbid-overwrite", "true");
                initiateMultipartUploadRequest.setObjectMetadata(metadata);
    
                InitiateMultipartUploadResult initiateMultipartUploadResult = ossClient.initiateMultipartUpload(initiateMultipartUploadRequest);
                String uploadId = initiateMultipartUploadResult.getUploadId();
    
                // 分片拷贝。
                List<PartETag> partETags = new ArrayList<PartETag>();
                for (int i = 0; i < partCount; i++) {
                    // 计算每个分片的大小。
                    long skipBytes = partSize * i;
                    long size = partSize < contentLength - skipBytes ? partSize : contentLength - skipBytes;
    
                    // 创建UploadPartCopyRequest。可以通过UploadPartCopyRequest指定限定条件。
                    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);
    
                    // 将返回的分片ETag保存到partETags中。
                    partETags.add(uploadPartCopyResult.getPartETag());
                }
    
                // 完成分片拷贝任务。
                CompleteMultipartUploadRequest completeMultipartUploadRequest = new CompleteMultipartUploadRequest(
                        destinationBucketName, destinationObjectName, uploadId, partETags);
    
                // 指定拷贝文件操作时是否覆盖同名Object。
                // 不指定x-oss-forbid-overwrite时,默认覆盖同名Object
                // 指定x-oss-forbid-overwrite为false时,表示允许覆盖同名Object。
                // 指定x-oss-forbid-overwrite为true时,表示禁止覆盖同名Object,如果同名Object已存在,程序将报错。
                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();
                }
            }
        }
    }

分片上传

以下代码用于分片上传时禁止覆盖同名文件:

import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSS;
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 {
        // Endpoint以华东1(杭州)为例,其它Region请按实际情况填写。
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // 阿里云账号AccessKey拥有所有API的访问权限,风险很高。强烈建议您创建并使用RAM用户进行API访问或日常运维,请登录RAM控制台创建RAM用户。
        String accessKeyId = "yourAccessKeyId";
        String accessKeySecret = "yourAccessKeySecret";
        // 填写Bucket名称,例如examplebucket。
        String bucketName = "examplebucket";
        // 填写Object的完整路径。Object完整路径中不能包含Bucket名称。
        String objectName = "exampledir/object";

        // 创建OSSClient实例。
        OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);

        try {
            // 创建InitiateMultipartUploadRequest对象。
            InitiateMultipartUploadRequest request = new InitiateMultipartUploadRequest(bucketName, objectName);

            // 指定分片上传操作时是否覆盖同名Object。
            // 不指定x-oss-forbid-overwrite时,默认覆盖同名Object。
            // 指定x-oss-forbid-overwrite为false时,表示允许覆盖同名Object。
            // 指定x-oss-forbid-overwrite为true时,表示禁止覆盖同名Object,如果同名Object已存在,程序将报错。
            ObjectMetadata metadata = new ObjectMetadata();
            metadata.setHeader("x-oss-forbid-overwrite", "true");
            request.setObjectMetadata(metadata);

            // 初始化分片。
            InitiateMultipartUploadResult upresult = ossClient.initiateMultipartUpload(request);
            // 返回uploadId,它是分片上传事件的唯一标识,您可以根据这个ID来发起相关的操作,如取消分片上传、查询分片上传等。
            String uploadId = upresult.getUploadId();

            // partETags是PartETag的集合。PartETag由分片的ETag和分片号组成。
            List<PartETag> partETags =  new ArrayList<PartETag>();
            // 计算文件有多少个分片。
            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++;
            }
            // 遍历分片上传。
            for (int i = 0; i < partCount; i++) {
                long startPos = i * partSize;
                long curPartSize = (i + 1 == partCount) ? (fileLength - startPos) : partSize;
                InputStream instream = new FileInputStream(sampleFile);
                // 跳过已经上传的分片。
                instream.skip(startPos);
                UploadPartRequest uploadPartRequest = new UploadPartRequest();
                uploadPartRequest.setBucketName(bucketName);
                uploadPartRequest.setKey(objectName);
                uploadPartRequest.setUploadId(uploadId);
                uploadPartRequest.setInputStream(instream);
                // 设置分片大小。除了最后一个分片没有大小限制,其他的分片最小为100KB。
                uploadPartRequest.setPartSize(curPartSize);
                // 设置分片号。每一个上传的分片都有一个分片号,取值范围是1~10000,如果超出这个范围,OSS将返回InvalidArgument的错误码。
                uploadPartRequest.setPartNumber( i + 1);
                // 每个分片不需要按顺序上传,甚至可以在不同客户端上传,OSS会按照分片号排序组成完整的文件。
                UploadPartResult uploadPartResult = ossClient.uploadPart(uploadPartRequest);
                // 每次上传分片之后,OSS的返回结果会包含一个PartETag。PartETag将被保存到partETags中。
                partETags.add(uploadPartResult.getPartETag());
            }


            // 创建CompleteMultipartUploadRequest对象。
            // 完成分片上传操作时,需要提供所有有效的partETags。OSS收到提交的partETags后,会逐一验证每个分片的有效性。当所有的数据分片验证通过后,OSS将把这些分片组合成一个完整的文件。
            CompleteMultipartUploadRequest completeMultipartUploadRequest =
                    new CompleteMultipartUploadRequest(bucketName, objectName, uploadId, partETags);

            // 指定分片上传操作时是否覆盖同名Object。
            // 不指定x-oss-forbid-overwrite时,默认覆盖同名Object。
            // 指定x-oss-forbid-overwrite为false时,表示允许覆盖同名Object。
            // 指定x-oss-forbid-overwrite为true时,表示禁止覆盖同名Object,如果同名Object已存在,程序将报错。
            completeMultipartUploadRequest.addHeader("x-oss-forbid-overwrite", "true");

            // 完成上传。
            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();
            }
        }
    }
}

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