How do I read the content of a file in Amazon S3

Question

I have a file in Amazon S3 in bucket ABCD. I have 3 objects ("folderA/folderB/folderC/abcd.csv") which are folders and in the final folder I have a .csv file (abcd.csv). I have used a logic to convert it to JSON and load it back into another file which is a .txt file in the same folder ("folderA/folderB/folderC/abcd.txt"). I had to download the file locally in order to do that. How would I read the file directly and write it back to the text file. The code which I have used to write to a file in S3 is below and I need to read a file from S3.

 InputStream inputStream = new ByteArrayInputStream(json.getBytes(StandardCharsets.UTF_16));
 ObjectMetadata metadata = new ObjectMetadata();
 metadata.setContentLength(json.length());
 PutObjectRequest request = new PutObjectRequest(bucketPut, filePut, inputStream, metadata);
 s3.putObject(request);

Answer 1

First you should get the object InputStream to do your need.

S3Object object = s3Client.getObject(new GetObjectRequest(bucketName, key));
InputStream objectData = object.getObjectContent();

Pass the InputStream, File Name and the path to the below method to download your stream.

public void saveFile(String fileName, String path, InputStream objectData) throws Exception {
    DataOutputStream dos = null;
    OutputStream out = null;
    try {
        File newDirectory = new File(path);
        if (!newDirectory.exists()) {
            newDirectory.mkdirs();
        }

        File uploadedFile = new File(path, uploadFileName);
        out = new FileOutputStream(uploadedFile);
        byte[] fileAsBytes = new byte[inputStream.available()];
        inputStream.read(fileAsBytes);

        dos = new DataOutputStream(out);
        dos.write(fileAsBytes);
    } catch (IOException io) {
        io.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            if (out != null) {
                out.close();
            }
            if (dos != null) {
                dos.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

After you Download your object read the file and make it to JSON and write it to .txt file after that you can upload the txt file to the desired bucket in S3