文件 AWS 開發套件範例 GitHub 儲存庫中有更多可用的 [AWS SDK 範例](https://github.com/awsdocs/aws-doc-sdk-examples)。

本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 使用檢查總和來使用 AWS SDK 處理 Amazon S3 物件
<a name="s3_example_s3_Scenario_UseChecksums_section"></a>

下列程式碼範例示範如何使用總和檢查搭配 Amazon S3 物件。

------
#### [ Java ]

**SDK for Java 2.x**  
 GitHub 上提供更多範例。尋找完整範例，並了解如何在 [AWS 程式碼範例儲存庫](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javav2/example_code/s3#code-examples)中設定和執行。
這些程式碼範例使用下列匯入的子集。  

```
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import software.amazon.awssdk.core.exception.SdkException;
import software.amazon.awssdk.core.sync.RequestBody;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.ChecksumAlgorithm;
import software.amazon.awssdk.services.s3.model.ChecksumMode;
import software.amazon.awssdk.services.s3.model.CompletedMultipartUpload;
import software.amazon.awssdk.services.s3.model.CompletedPart;
import software.amazon.awssdk.services.s3.model.CreateMultipartUploadResponse;
import software.amazon.awssdk.services.s3.model.GetObjectResponse;
import software.amazon.awssdk.services.s3.model.UploadPartRequest;
import software.amazon.awssdk.services.s3.model.UploadPartResponse;
import software.amazon.awssdk.services.s3.waiters.S3Waiter;
import software.amazon.awssdk.transfer.s3.S3TransferManager;
import software.amazon.awssdk.transfer.s3.model.FileUpload;
import software.amazon.awssdk.transfer.s3.model.UploadFileRequest;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.file.Paths;
import java.security.DigestInputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.Base64;
import java.util.List;
import java.util.Objects;
import java.util.UUID;
```
當您[建置 `PutObjectRequest`](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/model/PutObjectRequest.Builder.html)時，為 `putObject` 方法指定總和檢查演算法。  

```
    public void putObjectWithChecksum() {
        s3Client.putObject(b -> b
                .bucket(bucketName)
                .key(key)
                .checksumAlgorithm(ChecksumAlgorithm.CRC32),
            RequestBody.fromString("This is a test"));
    }
```
當您[建置 GetObjectRequest](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/model/GetObjectRequest.Builder.html) 時，請驗證 `getObject` 方法的總和檢查。  

```
    public GetObjectResponse getObjectWithChecksum() {
        return s3Client.getObject(b -> b
                .bucket(bucketName)
                .key(key)
                .checksumMode(ChecksumMode.ENABLED))
            .response();
    }
```
當您[建置 `PutObjectRequest`](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/model/PutObjectRequest.Builder.html)時，為 `putObject` 方法預先計算總和檢查。  

```
    public void putObjectWithPrecalculatedChecksum(String filePath) {
        String checksum = calculateChecksum(filePath, "SHA-256");

        s3Client.putObject((b -> b
                .bucket(bucketName)
                .key(key)
                .checksumSHA256(checksum)),
            RequestBody.fromFile(Paths.get(filePath)));
    }
```
除了 [AWS CRT 型 S3 用戶端](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/crt-based-s3-client.html)之外，內容大小超過閾值時使用 [S3 Transfer Manager](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/transfer-manager.html) 明確執行分段上傳。預設閾值大小為 8 MB。  
您可以指定要讓 SDK 使用的總和檢查演算法。根據預設，SDK 會使用 CRC32 演算法。  

```
    public void multipartUploadWithChecksumTm(String filePath) {
        S3TransferManager transferManager = S3TransferManager.create();
        UploadFileRequest uploadFileRequest = UploadFileRequest.builder()
            .putObjectRequest(b -> b
                .bucket(bucketName)
                .key(key)
                .checksumAlgorithm(ChecksumAlgorithm.SHA1))
            .source(Paths.get(filePath))
            .build();
        FileUpload fileUpload = transferManager.uploadFile(uploadFileRequest);
        fileUpload.completionFuture().join();
        transferManager.close();
    }
```
使用 [S3Client API](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/S3Client.html) 或（S3AsyncClient API）執行分段上傳。如果您指定額外的總和檢查，則必須指定在上傳初始化時要使用的演算法。您還必須為每一個分段請求指定演算法，並在每一個分段上傳後提供為其計算的總和檢查。  

```
    public void multipartUploadWithChecksumS3Client(String filePath) {
        ChecksumAlgorithm algorithm = ChecksumAlgorithm.CRC32;

        // Initiate the multipart upload.
        CreateMultipartUploadResponse createMultipartUploadResponse = s3Client.createMultipartUpload(b -> b
            .bucket(bucketName)
            .key(key)
            .checksumAlgorithm(algorithm)); // Checksum specified on initiation.
        String uploadId = createMultipartUploadResponse.uploadId();

        // Upload the parts of the file.
        int partNumber = 1;
        List<CompletedPart> completedParts = new ArrayList<>();
        ByteBuffer bb = ByteBuffer.allocate(1024 * 1024 * 5); // 5 MB byte buffer

        try (RandomAccessFile file = new RandomAccessFile(filePath, "r")) {
            long fileSize = file.length();
            long position = 0;
            while (position < fileSize) {
                file.seek(position);
                long read = file.getChannel().read(bb);

                bb.flip(); // Swap position and limit before reading from the buffer.
                UploadPartRequest uploadPartRequest = UploadPartRequest.builder()
                    .bucket(bucketName)
                    .key(key)
                    .uploadId(uploadId)
                    .checksumAlgorithm(algorithm) // Checksum specified on each part.
                    .partNumber(partNumber)
                    .build();

                UploadPartResponse partResponse = s3Client.uploadPart(
                    uploadPartRequest,
                    RequestBody.fromByteBuffer(bb));

                CompletedPart part = CompletedPart.builder()
                    .partNumber(partNumber)
                    .checksumCRC32(partResponse.checksumCRC32()) // Provide the calculated checksum.
                    .eTag(partResponse.eTag())
                    .build();
                completedParts.add(part);

                bb.clear();
                position += read;
                partNumber++;
            }
        } catch (IOException e) {
            System.err.println(e.getMessage());
        }

        // Complete the multipart upload.
        s3Client.completeMultipartUpload(b -> b
            .bucket(bucketName)
            .key(key)
            .uploadId(uploadId)
            .multipartUpload(CompletedMultipartUpload.builder().parts(completedParts).build()));
    }
```
+ 如需 API 詳細資訊，請參閱《*AWS SDK for Java 2.x API 參考*》中的下列主題。
  + [CompleteMultipartUpload](https://docs.aws.amazon.com/goto/SdkForJavaV2/s3-2006-03-01/CompleteMultipartUpload)
  + [CreateMultipartUpload](https://docs.aws.amazon.com/goto/SdkForJavaV2/s3-2006-03-01/CreateMultipartUpload)
  + [UploadPart](https://docs.aws.amazon.com/goto/SdkForJavaV2/s3-2006-03-01/UploadPart)

------