Ada lebih banyak contoh AWS SDK yang tersedia di repo Contoh [SDK AWS Doc](https://github.com/awsdocs/aws-doc-sdk-examples). GitHub 

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# Menggunakan checksum untuk bekerja dengan objek Amazon S3 menggunakan SDK AWS
<a name="s3_example_s3_Scenario_UseChecksums_section"></a>

Contoh kode berikut menunjukkan cara menggunakan checksum untuk bekerja dengan objek Amazon S3.

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

**SDK untuk Java 2.x**  
 Ada lebih banyak tentang GitHub. Temukan contoh lengkapnya dan pelajari cara mengatur dan menjalankannya di [Repositori Contoh Kode AWS](https://github.com/awsdocs/aws-doc-sdk-examples/tree/main/javav2/example_code/s3#code-examples). 
Contoh kode menggunakan subset dari impor berikut.  

```
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;
```
Tentukan algoritma checksum untuk metode `putObject` saat Anda [membangun `PutObjectRequest`](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/model/PutObjectRequest.Builder.html).  

```
    public void putObjectWithChecksum() {
        s3Client.putObject(b -> b
                .bucket(bucketName)
                .key(key)
                .checksumAlgorithm(ChecksumAlgorithm.CRC32),
            RequestBody.fromString("This is a test"));
    }
```
Verifikasi checksum untuk `getObject` metode saat Anda [membangun. GetObjectRequest](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/model/GetObjectRequest.Builder.html)  

```
    public GetObjectResponse getObjectWithChecksum() {
        return s3Client.getObject(b -> b
                .bucket(bucketName)
                .key(key)
                .checksumMode(ChecksumMode.ENABLED))
            .response();
    }
```
Hitung terlebih dahulu checksum untuk metode `putObject` saat Anda [membangun `PutObjectRequest`](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/model/PutObjectRequest.Builder.html).  

```
    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)));
    }
```
Gunakan [Manajer Transfer S3](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/transfer-manager.html) di atas [klien S3 AWS berbasis CRT](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/crt-based-s3-client.html) untuk melakukan unggahan multibagian secara transparan ketika ukuran konten melebihi ambang batas. Ukuran ambang default adalah 8 MB.  
Anda dapat menentukan algoritma checksum untuk SDK yang akan digunakan. Secara default, SDK menggunakan CRC32 algoritma.  

```
    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();
    }
```
Gunakan [S3Client API](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/services/s3/S3Client.html) atau (S3 AsyncClient API) untuk melakukan upload multipart. Jika Anda menentukan checksum tambahan, Anda juga harus menentukan algoritma yang akan digunakan pada inisiasi unggahan. Anda juga harus menentukan algoritma untuk setiap permintaan bagian dan memberikan checksum yang dihitung untuk setiap bagian setelah diunggah.  

```
    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()));
    }
```
+ Untuk detail API, lihat topik berikut di *Referensi API AWS SDK for Java 2.x *.
  + [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)

------