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Thread: How to append batches of stream data to one CSV file using Java NIO Package

  1. #1
    Junior Member
    Join Date
    Feb 2022
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    Question How to append batches of stream data to one CSV file using Java NIO Package

    I am reading data from API response in batches of bytes which is of Content-Type = text/CSV and using Java's NIO package to transfer bytes between two Channels. I want to write API responses in batches to the same File (APPEND). With below code append doesn't seem to work correctly, it's more of overriding results.
    And once all the data is written then I also want to print the number of total lines in CSV.

    private void downloadFile_NIO(String encoded_token) throws Exception 
          long start_Range = 0;
        long end_Range = 5000;
        long batch_size = 5000;
        long totalsize = 1080612174;
        long counter = 0;
        //Path path = Paths.get(FILE_NAME);
        //long lines = 0;
        while (start_Range <= totalsize)
           URL url = new URL(FILE_URL);
           HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
           connection.setRequestProperty("Authorization", "Bearer " + encoded_token );
           ReadableByteChannel readableByteChannel = Channels.newChannel(connection.getInputStream());
            FileOutputStream fileOutputStream=new FileOutputStream(new File(FILE_NAME),true);
           fileOutputStream.getChannel().transferFrom(readableByteChannel, 0, Long.MAX_VALUE);
           // lines = Files.lines(path).count();
          // System.out.println("lines->" + lines);
            counter = counter + 1;
            if (counter < 2)
               start_Range = start_Range + batch_size + 1;
               end_Range = end_Range + batch_size;
                start_Range = start_Range + batch_size;
                   end_Range = end_Range + batch_size;

  2. #2
    Super Moderator Norm's Avatar
    Join Date
    May 2010
    Eastern Florida
    Thanked 2,709 Times in 2,659 Posts

    Default Re: How to append batches of stream data to one CSV file using Java NIO Package

    Can you provide a small complete program that compiles and executes for testing?

    --- Update ---

    Also posted here: https://coderanch.com/t/749839/java/...tream-data-CSV
    If you don't understand my answer, don't ignore it, ask a question.

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