Resume http file download in java

 HttpURLConnection connection = (HttpURLConnection) url.openConnection();    if(ISSUE_DOWNLOAD_STATUS.intValue()==ECMConstant.ECM_DOWNLOADING){        File file=new File(DESTINATION_PATH);        if(file.exists()){             downloaded = (int) file.length();             connection.setRequestProperty("Range", "bytes="+(file.length())+"-");        }    }else{        connection.setRequestProperty("Range", "bytes=" + downloaded + "-");    }    connection.setDoInput(true);    connection.setDoOutput(true);    progressBar.setMax(connection.getContentLength());     in = new BufferedInputStream(connection.getInputStream());     fos=(downloaded==0)? new FileOutputStream(DESTINATION_PATH): new FileOutputStream(DESTINATION_PATH,true);     bout = new BufferedOutputStream(fos, 1024);    byte[] data = new byte[1024];    int x = 0;    while ((x = in.read(data, 0, 1024)) >= 0) {        bout.write(data, 0, x);         downloaded += x;         progressBar.setProgress(downloaded);    }

This is not my code, but it works.

I guess the problem you are facing is calling url.openStream() after url.openConnection().

url.openStream() is equivalent to url.openConnection().getInputStream(). Hence, you are requesting the url twice. Particularly the second time, it is not specifying the range property. Therefore download always starts at the beginning.

You should replace url.openStream() with connection.getInputStream().

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 downloaded file will be saved. * @param downloadURL = File downloading 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;}}