Is there a callback function concept in Java to do async I/O as it is in Javascript?

Question

I am a Javascript front-end developer, but need to write a simple Java program to write file and sent Email and HTTP request.

Here is the Java code that I use to write log to disk file:

    @Override
public void log(String text) {
    Date date = new Date();
    DateFormat sdf = new SimpleDateFormat("yyyyMMdd");
    DateFormat sdf1 = new SimpleDateFormat("HH:mm:ss");
    String logDateString = sdf.format(date);
    //System.out.println("logDateString: " + logDateString);
    BufferedWriter bwToUse = null;
    if(logDateString.compareTo(m_firstOpenDate) == 0) {
        // use old buffer writer
        bwToUse = this.m_bw;
    } else {
        // generate new buffer writer
        // update m_firstOpenDate
        m_firstOpenDate = logDateString;


        try {
            // close previous day log
            this.m_bw.close();
            this.m_fw = new FileWriter(m_path + logDateString + ".log", true);
            this.m_bw = new BufferedWriter(this.m_fw);
            bwToUse = this.m_bw;
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    try {
        bwToUse.write(sdf1.format(date) + ": " + text + "\n");
        bwToUse.flush();


    } catch (IOException e) {
        e.printStackTrace();
    }
}

You can ignore the detail.

My real question is that for those heavy IO operation, e.g.: file reading, sending email and making HTTP request(post data to a web hook), how to do it in a non-blocking async way in Java? I know it is standard in Javascript to use callback, but in Java, how do you do async http request?

Thanks!

Answer 1

The closest concept in Java is Future.

But you should be aware that Java has a multithreading concurrency model, as opposed to single-threaded JavaScript with asynchronous concurrency model. If you're new to this concept, then you better start with a Tutorial.

Also for IO-operations you should consider non-blocking IO API.

Answer 2

You can use FutureTask. You should implemets Callable interface. Here is a sample