Question

I wrote a thread program in Java to download a file from URL (https). Sometimes the size of the file downloaded is reduced from its original size.

How to download file without losing data?

Code

public class Download extends Observable implements Runnable {
    private static final int MAX_BUFFER_SIZE = 1024;        
    public static final int DOWNLOADING = 0;    
    public static final int PAUSED = 1; 
    public static final int COMPLETE = 2;   
    public static final int CANCELLED = 3;  
    public static final int ERROR = 4;  
    private URL url; 
    private int size; 
    private int downloaded; 
    private int status; 
    
    public Download(URL url){
        this.url = url;
        size=-1;
        downloaded=0;
        status=DOWNLOADING;
        download();
    }
    
    public String getURL(){
        return url.toString();
    }   
    
    public void error(){
        status = ERROR;
        stateChanged();
    }
    
    private void download(){
        Thread thread = new Thread(this);
        thread.start();
    }

    @Override
    public void run() {     
        RandomAccessFile randomAccessFile = null;
        InputStream inputStream = null;
        try{
            HttpsURLConnection connection = getSSLCertficate(getURL());
            connection.setRequestMethod("GET");
            connection.setRequestProperty("Range","bytes=" + downloaded + "-");
            connection.connect();
            if(connection.getResponseCode()/100 != 2){
                error();
            }
            int contentLength = connection.getContentLength();
            if(contentLength <1){
                error();
            }
            if(size == -1){
                size = contentLength;
                stateChanged();
            }
            randomAccessFile = new RandomAccessFile("/home/user/Desktop/dotproject-2.1.5.tar.gz","rw");         
            randomAccessFile.seek(downloaded);
            inputStream = connection.getInputStream();
            while(status == DOWNLOADING){
                byte buffer[];
                int finalSize=size - downloaded;
                if ( finalSize > MAX_BUFFER_SIZE) {
                    buffer = new byte[MAX_BUFFER_SIZE];
                } else {
                    buffer = new byte[size - downloaded];
                }
                int read = inputStream.read(buffer);
                if(read == -1)
                    break;              
                
                randomAccessFile.write(buffer, 0, read);                
                downloaded += read;             
                stateChanged();
            }           
            
        }catch (Exception e) {
            
        }
    }
    
    private void stateChanged(){
        setChanged();
        notifyObservers();
    }
    
    private HttpsURLConnection getSSLCertficate(String urlPath) throws NoSuchAlgorithmException, KeyManagementException, IOException{
        SSLContext ctx = SSLContext.getInstance("TLS");
        ctx.init(new KeyManager[0],new TrustManager[]{new DefaultTrustManager()},new SecureRandom());
        SSLContext.setDefault(ctx);
        
        URL url = new URL(urlPath);
        HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();
        conn.setHostnameVerifier(new HostnameVerifier() {
            
            @Override
            public boolean verify(String arg0, SSLSession arg1) {               
                return true;
            }
        });
        
        return conn;
    }

    public static void main(String[] args) throws MalformedURLException {
        Download d = new Download(new URL("https://192.16.1.130/Source.tar.gz"));
        d.run();
    }

}

Answer 1

Please close your input stream in finally section (than it automatically flush all data):

try {
    ....
} catch(...) {
    ...
} finally {
    // This will guaranty you get all data:
    inputStream.close();
}