Resume http file download in java

Question

URL url = new URL("http://download.thinkbroadband.com/20MB.zip");

URLConnection connection = url.openConnection();
File fileThatExists = new File(path); 
OutputStream output = new FileOutputStream(path, true);
connection.setRequestProperty("Range", "bytes=" + fileThatExists.length() + "-");

connection.connect();

int lenghtOfFile = connection.getContentLength();

InputStream input = new BufferedInputStream(url.openStream());
byte data[] = new byte[1024];

long total = 0;

while ((count = input.read(data)) != -1) {
    total += count;

    output.write(data, 0 , count);
}

in this code I try to resume download. Target file is 20MB. But when I stop download on 10mb, then contunue, I get file with filesize 30MB. It seems that it continue writing to file, but cant partly download from server. Wget -c works great with this file. How can I resume file download?

Answer 1

This is what I am using to download the file in chunk Updating the UI with progress.

/ ** @param callback = To update the UI with appropriate action

 * @param fileName = Name of the file by which downlaoded file will be saved.
 * @param downloadURL = File downlaoding URL
 * @param filePath = Path where file will be saved
 * @param object = Any object you want in return after download is completed to do certain operations like insert in DB or show toast
 */

public void startDownload(final IDownloadCallback callback, String fileName, String downloadURL, String filePath, Object object) {
    callback.onPreExecute(); // Callback to tell that the downloading is going to start
    int count = 0;
    File outputFile = null; // Path where file will be downloaded
    try {
        File file = new File(filePath);
        file.mkdirs();
        long range = 0;
        outputFile = new File(file, fileName);
        /**
         * Check whether the file exists or not
         * If file doesn't exists then create the new file and range will be zero.
         * But if file exists then get the length of file which will be the starting range,
         * from where the file will be downloaded
         */
        if (!outputFile.exists()) {
            outputFile.createNewFile();
            range = 0;
        } else {
            range = outputFile.length();
        }
        //Open the Connection
        URL url = new URL(downloadURL);
        URLConnection con = url.openConnection();
        // Set the range parameter in header and give the range from where you want to start the downloading
        con.setRequestProperty("Range", "bytes=" + range + "-");
        /**
         * The total length of file will be the total content length given by the server + range.
         * Example: Suppose you have a file whose size is 1MB and you had already downloaded 500KB of it.
         * Then you will pass in Header as "Range":"bytes=500000".
         * Now the con.getContentLength() will be 500KB and range will be 500KB.
         * So by adding the two you will get the total length of file which will be 1 MB
         */
        final long lenghtOfFile = (int) con.getContentLength() + range;

        FileOutputStream fileOutputStream = new FileOutputStream(outputFile, true);
        InputStream inputStream = con.getInputStream();

        byte[] buffer = new byte[1024];

        long total = range;
        /**
         * Download the save the content into file
         */
        while ((count = inputStream.read(buffer)) != -1) {
            total += count;
            int progress = (int) (total * 100 / lenghtOfFile);
            EntityDownloadProgress entityDownloadProgress = new EntityDownloadProgress();
            entityDownloadProgress.setProgress(progress);
            entityDownloadProgress.setDownloadedSize(total);
            entityDownloadProgress.setFileSize(lenghtOfFile);
            callback.showProgress(entityDownloadProgress);
            fileOutputStream.write(buffer, 0, count);
        }
        //Close the outputstream
        fileOutputStream.close();
        // Disconnect the Connection
        if (con instanceof HttpsURLConnection) {
            ((HttpsURLConnection) con).disconnect();
        } else if (con instanceof HttpURLConnection) {
            ((HttpURLConnection) con).disconnect();
        }
        inputStream.close();
        /**
         * If file size is equal then return callback as success with downlaoded filepath and the object
         * else return failure
         */
        if (lenghtOfFile == outputFile.length()) {
            callback.onSuccess(outputFile.getAbsolutePath(), object);
        } else {
            callback.onFailure(object);
        }
    } catch (Exception e) {
        e.printStackTrace();
        callback.onFailure(object);
    }
}

interface IDownloadCallback {

    void onPreExecute(); // Callback to tell that the downloading is going to start
    void onFailure(Object o); // Failed to download file
    void onSuccess(String path, Object o); // Downloaded file successfully with downloaded path
    void showProgress(EntityDownloadProgress entityDownloadProgress); // Show progress
}

public class EntityDownloadProgress {

    int progress; // range from 1-100
    long fileSize;// Total size of file to be downlaoded
    long downloadedSize; // Size of the downlaoded file

    public void setProgress(int progress) {this.progress = progress;}

    public void setFileSize(long fileSize) {this.fileSize = fileSize;}

    public void setDownloadedSize(long downloadedSize) {this.downloadedSize = downloadedSize;}
}