Question

I am trying to implement multithreading using ExecutorService for downloading files parallely. Below is my code

   public void downloadFiles(List<String> filenames, final String fileSavePath) {
    if (filenames != null && filenames.size() > 0) {
        List<Callable<Void>> jobs = new ArrayList();
        for (final String fileName : filenames) {
            jobs.add(new Callable() {
                public Void call() throws Exception {
                    downloadFile(fileName, fileSavePath);
                    return null;
                }
            });
        }
        performJobs(jobs);
    }
}

My requirement is that i want to return a status from this method after all the files are downloaded succesfully. I am not sure how to do this. I cannot access variable of inner class from an outer one.

Any advice would be appreciable.

Thanks

Answer 1

From the Javadoc of Callable:

A task that returns a result and may throw an exception. Implementors
define a single method with no arguments called call.

Taking a cue from this, change List<Callable<Void>> jobs to List<Callable<Boolean>> jobs and similarly change your return type of your call method. Using this, after completion of the task, you can then check the returned status.