Get an Amazon S3 object deserialized to a Java object

Question

I have a user defined object, say MyClass, saved in an Amazon S3 bucket inside a folder. The bucket structure looks like the following:

<bucket>
-<folder>
--<my unique numbered file containing MyClass>

I need to read this file and deserialize it to MyClass.

I went through AWS docs and it suggested to use something like the following

Regions clientRegion = Regions.DEFAULT_REGION;
 String bucketName = "*** Bucket name ***";
 String key = "*** Object key ***";

 S3Object fullObject = null, objectPortion = null, headerOverrideObject = null;
 try {
            AmazonS3 s3Client = AmazonS3ClientBuilder.standard()
                    .withRegion(clientRegion)
                    .withCredentials(new ProfileCredentialsProvider())
                    .build();

   fullObject = s3Client.getObject(new GetObjectRequest(bucketName, key));

Example: https://docs.aws.amazon.com/AmazonS3/latest/userguide/download-objects.html

However, I need to deserialize it to MyClass instead of S3Object. I couldn't get an example of how to do this. Can anyone suggest how this is done?

Answer 1

You are looking in the correct Guide - wrong topic for latest Java API to use. The topic you are looking at is old V1 code.

Look at this topic to use AWS SDK for Java V2 - which is considered best practice. V2 packages start with software.amazon.awssdk.

https://docs.aws.amazon.com/AmazonS3/latest/userguide/example_s3_GetObject_section.html

Once you get an object from an S3 bucket, you can convert it into a byte array and from there - do what ever you need to. This V2 example shows how to get a byte array from an object.

package com.example.s3;

// snippet-start:[s3.java2.getobjectdata.import]
import software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider;
import software.amazon.awssdk.core.ResponseBytes;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.GetObjectRequest;
import software.amazon.awssdk.services.s3.model.S3Exception;
import software.amazon.awssdk.services.s3.model.GetObjectResponse;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
// snippet-end:[s3.java2.getobjectdata.import]

/**
 * Before running this Java V2 code example, set up your development environment, including your credentials.
 *
 * For more information, see the following documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */

public class GetObjectData {

    public static void main(String[] args) {

     final String usage = "\n" +
                "Usage:\n" +
                "    <bucketName> <keyName> <path>\n\n" +
                "Where:\n" +
                "    bucketName - The Amazon S3 bucket name. \n\n"+
                "    keyName - The key name. \n\n"+
                "    path - The path where the file is written to. \n\n";

        if (args.length != 3) {
            System.out.println(usage);
            System.exit(1);
        }

        String bucketName = args[0];
        String keyName = args[1];
        String path = args[2];

        ProfileCredentialsProvider credentialsProvider = ProfileCredentialsProvider.create();
        Region region = Region.US_EAST_1;
        S3Client s3 = S3Client.builder()
                .region(region)
                .credentialsProvider(credentialsProvider)
                .build();

        getObjectBytes(s3,bucketName,keyName, path);
        s3.close();
    }

    // snippet-start:[s3.java2.getobjectdata.main]
    public static void getObjectBytes (S3Client s3, String bucketName, String keyName, String path ) {

        try {
            GetObjectRequest objectRequest = GetObjectRequest
                    .builder()
                    .key(keyName)
                    .bucket(bucketName)
                    .build();

            ResponseBytes<GetObjectResponse> objectBytes = s3.getObjectAsBytes(objectRequest);
            byte[] data = objectBytes.asByteArray();

            // Write the data to a local file.
            File myFile = new File(path );
            OutputStream os = new FileOutputStream(myFile);
            os.write(data);
            System.out.println("Successfully obtained bytes from an S3 object");
            os.close();

        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (S3Exception e) {
          System.err.println(e.awsErrorDetails().errorMessage());
           System.exit(1);
        }
    }
    // snippet-end:[s3.java2.getobjectdata.main]
}