source: java/HTTPFileDownloader/src/net/oni2/httpfiledownloader/FileDownloader.java@ 1133

package net.oni2.httpfiledownloader;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.URL;
import java.net.URLConnection;
import java.util.HashSet;

import net.oni2.ProxySettings;

/**
 * @author Christian Illy
 */
public class FileDownloader implements Runnable {
        /**
         * @author Christian Illy
         */
        public enum EState {
                /**
                 * Downloader initialized but not started
                 */
                INIT,
                /**
                 * Download running
                 */
                RUNNING,
                /**
                 * Download suspended
                 */
                PAUSED,
                /**
                 * Download interrupted
                 */
                INTERRUPTED,
                /**
                 * Download finished successfully
                 */
                FINISHED,
                /**
                 * Aborted because of an error
                 */
                ERROR
        };

        private HashSet<FileDownloadListener> listeners = new HashSet<FileDownloadListener>();
        private Thread t = null;
        private URL url = null;
        private File target = null;
        private int fileLength = Integer.MAX_VALUE;
        private int downloaded = 0;

        private EState state = EState.INIT;

        /**
         * @param url
         *            URL of file to download
         * @param target
         *            Path of target file to save to
         * @throws IOException
         *             If url could not be opened
         */
        public FileDownloader(String url, File target) throws IOException {
                this.url = new URL(url);
                this.target = target;
        }

        /**
         * @param listener
         *            Listener to add
         */
        public void addListener(FileDownloadListener listener) {
                listeners.add(listener);
        }

        /**
         * @param listener
         *            Listener to remove
         */
        public void removeListener(FileDownloadListener listener) {
                listeners.remove(listener);
        }

        /**
         * Start the download process
         */
        public synchronized void start() {
                if (t == null) {
                        state = EState.RUNNING;
                        t = new Thread(this);
                        t.start();
                }
        }

        /**
         * @param suspend
         *            Suspend or resume
         */
        public synchronized void suspend(boolean suspend) {
                if ((state == EState.RUNNING) || (state == EState.PAUSED)) {
                        if (suspend)
                                state = EState.PAUSED;
                        else
                                state = EState.RUNNING;
                        updateStatus(downloaded, fileLength);
                }
        }

        /**
         * Stop (abort) download
         */
        public synchronized void stop() {
                if (state != EState.FINISHED) {
                        state = EState.INTERRUPTED;
                        if (t != null) {
                                try {
                                        t.join();
                                } catch (InterruptedException e) {
                                        e.printStackTrace();
                                }
                                t = null;
                        }
                        updateStatus(0, 1);
                        if (target.exists())
                                target.delete();
                }
        }

        /**
         * @return current state
         */
        public EState getState() {
                return state;
        }

        private synchronized void updateStatus(int current, int total) {
                downloaded = current;
                for (FileDownloadListener l : listeners) {
                        l.statusUpdate(this, state, current, total);
                }
        }

        @Override
        public void run() {
                int downloaded = 0;
                String strLastModified = null;
                String strEtag = null;
                RandomAccessFile outFile = null;

                try {
                        outFile = new RandomAccessFile(target, "rw");
                } catch (FileNotFoundException e1) {
                        e1.printStackTrace();
                        state = EState.ERROR;
                        updateStatus(downloaded, fileLength);
                        return;
                }

                try {
                        while (downloaded < fileLength) {
                                switch (state) {
                                        case ERROR:
                                                updateStatus(downloaded, fileLength);
                                                return;
                                        case PAUSED:
                                                try {
                                                        Thread.sleep(100);
                                                } catch (InterruptedException e) {
                                                        e.printStackTrace();
                                                }
                                                break;
                                        case INTERRUPTED:
                                                return;
                                        case RUNNING:
                                                BufferedInputStream input = null;
                                                try {
                                                        URLConnection connection = url
                                                                        .openConnection(ProxySettings.getInstance()
                                                                                        .getProxy());
                                                        connection.setRequestProperty("Cache-Control",
                                                                        "no-cache");
                                                        if (downloaded == 0) {
                                                                connection.connect();
                                                                strLastModified = connection
                                                                                .getHeaderField("Last-Modified");
                                                                strEtag = connection.getHeaderField("ETag");
                                                                fileLength = connection.getContentLength();
                                                        } else {
                                                                connection.setRequestProperty("Range", "bytes="
                                                                                + downloaded + "-");
                                                                if (strEtag != null)
                                                                        connection.setRequestProperty("If-Range",
                                                                                        strEtag);
                                                                else
                                                                        connection.setRequestProperty("If-Range",
                                                                                        strLastModified);
                                                                connection.connect();
                                                        }

                                                        // Setup streams and buffers.
                                                        input = new BufferedInputStream(
                                                                        connection.getInputStream(), 8192);
                                                        if (downloaded > 0)
                                                                outFile.seek(downloaded);
                                                        byte data[] = new byte[1024];

                                                        // Download file.
                                                        int dataRead = 0;
                                                        int i = 0;
                                                        while (((dataRead = input.read(data, 0, 1024)) != -1)
                                                                        && (state == EState.RUNNING)) {
                                                                outFile.write(data, 0, dataRead);
                                                                downloaded += dataRead;
                                                                if (downloaded >= fileLength)
                                                                        break;

                                                                i++;
                                                                if ((i % 50) == 0)
                                                                        updateStatus(downloaded, fileLength);
                                                        }
                                                        input.close();
                                                } catch (IOException e) {
                                                        // TODO Auto-generated catch block
                                                        e.printStackTrace();
                                                        try {
                                                                if (input != null)
                                                                        input.close();
                                                        } catch (IOException e2) {
                                                                e2.printStackTrace();
                                                        }
                                                }
                                                break;
                                        default:
                                                break;
                                }
                        }
                } finally {
                        try {
                                // Close streams.
                                outFile.close();
                        } catch (IOException e) {
                                e.printStackTrace();
                        }
                }

                state = EState.FINISHED;
                updateStatus(downloaded, fileLength);
        }

        /**
         * @return the target
         */
        public File getTarget() {
                return target;
        }

        /**
         * @return the downloaded size
         */
        public int getDownloaded() {
                return downloaded;
        }

}