Upload a stream of unknown size to an Amazon S3 object using an Amazon SDK

Use the Amazon CRT-based S3 Client.

import com.example.s3.util.AsyncExampleUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import software.amazon.awssdk.core.async.AsyncRequestBody;
import software.amazon.awssdk.core.async.BlockingInputStreamAsyncRequestBody;
import software.amazon.awssdk.core.exception.SdkException;
import software.amazon.awssdk.services.s3.S3AsyncClient;
import software.amazon.awssdk.services.s3.model.PutObjectResponse;

import java.io.ByteArrayInputStream;
import java.util.UUID;
import java.util.concurrent.CompletableFuture;

    /**
     * @param s33CrtAsyncClient - To upload content from a stream of unknown size, use the AWS CRT-based S3 client. For more information, see
     *                          https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/crt-based-s3-client.html.
     * @param bucketName - The name of the bucket.
     * @param key - The name of the object.
     * @return software.amazon.awssdk.services.s3.model.PutObjectResponse - Returns metadata pertaining to the put object operation.
     */
    public PutObjectResponse putObjectFromStream(S3AsyncClient s33CrtAsyncClient, String bucketName, String key) {

        BlockingInputStreamAsyncRequestBody body =
                AsyncRequestBody.forBlockingInputStream(null); // 'null' indicates a stream will be provided later.

        CompletableFuture<PutObjectResponse> responseFuture =
                s33CrtAsyncClient.putObject(r -> r.bucket(bucketName).key(key), body);

        // AsyncExampleUtils.randomString() returns a random string up to 100 characters.
        String randomString = AsyncExampleUtils.randomString();
        logger.info("random string to upload: {}: length={}", randomString, randomString.length());

        // Provide the stream of data to be uploaded.
        body.writeInputStream(new ByteArrayInputStream(randomString.getBytes()));

        PutObjectResponse response = responseFuture.join(); // Wait for the response.
        logger.info("Object {} uploaded to bucket {}.", key, bucketName);
        return response;
    }
}

Use the Amazon S3 Transfer Manager.

import com.example.s3.util.AsyncExampleUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import software.amazon.awssdk.core.async.AsyncRequestBody;
import software.amazon.awssdk.core.async.BlockingInputStreamAsyncRequestBody;
import software.amazon.awssdk.core.exception.SdkException;
import software.amazon.awssdk.transfer.s3.S3TransferManager;
import software.amazon.awssdk.transfer.s3.model.CompletedUpload;
import software.amazon.awssdk.transfer.s3.model.Upload;

import java.io.ByteArrayInputStream;
import java.util.UUID;

    /**
     * @param transferManager - To upload content from a stream of unknown size, use the S3TransferManager based on the AWS CRT-based S3 client.
     *                       For more information, see https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/transfer-manager.html.
     * @param bucketName - The name of the bucket.
     * @param key - The name of the object.
     * @return - software.amazon.awssdk.transfer.s3.model.CompletedUpload - The result of the completed upload.
     */
    public CompletedUpload uploadStream(S3TransferManager transferManager, String bucketName, String key) {

        BlockingInputStreamAsyncRequestBody body =
                AsyncRequestBody.forBlockingInputStream(null); // 'null' indicates a stream will be provided later.

        Upload upload = transferManager.upload(builder -> builder
                .requestBody(body)
                .putObjectRequest(req -> req.bucket(bucketName).key(key))
                .build());

        // AsyncExampleUtils.randomString() returns a random string up to 100 characters.
        String randomString = AsyncExampleUtils.randomString();
        logger.info("random string to upload: {}: length={}", randomString, randomString.length());

        // Provide the stream of data to be uploaded.
        body.writeInputStream(new ByteArrayInputStream(randomString.getBytes()));

        return upload.completionFuture().join();
    }
}