Download.java

import java.io.*;
import java.net.*;
import java.util.*;
// This class downloads a file from a URL.
class Download extends Observable implements Runnable {
// Max size of download buffer.
private static final int MAX_BUFFER_SIZE = 1024;
// These are the status names.
public static final String STATUSES[] = {"Downloading",
"Paused", "Complete", "Cancelled", "Error"};
// These are the status codes.
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; // download URL
private String saveDir; // dir to save file
private int size; // size of download in bytes
private int downloaded; // number of bytes downloaded
private int status; // current status of download
// Constructor for Download.
public Download(URL url, String saveDir) {
this.url = url;
this.saveDir = saveDir;
size = -1;
downloaded = 0;
status = DOWNLOADING;
// Begin the download.
download();
}
// Get this download's URL.
public String getUrl() {
return url.toString();
}
// Get this download's size.
public int getSize() {
return size;
}
// Get this download's progress.
public float getProgress() {
return ((float) downloaded / size) * 100;
}
// Get this download's status.
public int getStatus() {
return status;
}
// Pause this download.
public void pause() {
status = PAUSED;
stateChanged();
}
// Resume this download.
public void resume() {
status = DOWNLOADING;
stateChanged();
download();
}
// Cancel this download.
public void cancel() {
status = CANCELLED;
stateChanged();
}
// Mark this download as having an error.
private void error() {
    status = ERROR;
    stateChanged();
    }
    // Start or resume downloading.
    private void download() {
    Thread thread = new Thread(this);
    thread.start();
    }
    // Get file name portion of URL.
    private String getFileName(URL url) {
    String fileName = url.getFile();
    return fileName.substring(fileName.lastIndexOf('/') + 1);
    }
    // Download file.
    public void run() {
    RandomAccessFile file = null;
    InputStream stream = null;
    try {
    // Open connection to URL.
    HttpURLConnection connection =
    (HttpURLConnection) url.openConnection();
    // Specify what portion of file to download.
    connection.setRequestProperty("Range",
    "bytes=" + downloaded + "-");
    // Connect to server.
    connection.connect();
    // Make sure response code is in the 200 range.
    if (connection.getResponseCode() / 100 != 2) {
    error();
    }
    // Check for valid content length.
    int contentLength = connection.getContentLength();
    if (contentLength < 1) {
    error();
    }
    /* Set the size for this download if it
    hasn't been already set. */
    if (size == -1) {
    size = contentLength;
    stateChanged();
    }
    // Open file and seek to the end of it.
file = new RandomAccessFile(getFileName(url), "rw");
file.seek(downloaded);
stream = connection.getInputStream();
while (status == DOWNLOADING) {
/* Size buffer according to how much of the
file is left to download. */
byte buffer[];
if (size - downloaded > MAX_BUFFER_SIZE) {
buffer = new byte[MAX_BUFFER_SIZE];
} else {
buffer = new byte[size - downloaded];
}
// Read from server into buffer.
int read = stream.read(buffer);
if (read == -1)
break;
// Write buffer to file.
file.write(buffer, 0, read);
downloaded += read;
stateChanged();
}
/* Change status to complete if this point was
reached because downloading has finished. */
if (status == DOWNLOADING) {
status = COMPLETE;
stateChanged();
}
} catch (Exception e) {
error();
} finally {
// Close file.
if (file != null) {
try {

file.close();
} catch (Exception e) {}
}
// Close connection to server.
if (stream != null) {
try {
stream.close();
} catch (Exception e) {}
}
}
}
// Notify observers that this download's status has changed.
private void stateChanged() {
    setChanged();
    notifyObservers();
    }
    }