S3Upload.java

import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestStreamHandler;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.ObjectMetadata;
import com.amazonaws.services.s3.model.PutObjectRequest;
import com.amazonaws.services.s3.model.PutObjectResult;

import java.io.InputStream;
import java.io.OutputStream;

public class S3Upload implements RequestStreamHandler{

    private final String ACCESS_KEY = "";
    private final String SECRET_KEY = "";

    public void handleRequest(InputStream inputStream, OutputStream outputStream, Context context)  {
        //https://stackoverflow.com/a/41952575/5531761
        AmazonS3 s3Client = AmazonS3ClientBuilder.standard().withCredentials(
                new AWSStaticCredentialsProvider(
                        new BasicAWSCredentials(ACCESS_KEY, SECRET_KEY))).build();
        PutObjectResult putObjectResult= s3Client.putObject(new PutObjectRequest("codesupdates","file.txt",inputStream, new ObjectMetadata()));

    }
}