Sequence Diagram Download Manager

1. Use Case

2. Class Diagram

3. Sequence Diagram

4. Source Code Snip (in Java)
import java.io.*;
import java.net.*;
import java.util.*;

class Download extends Observable implements Runnable
{
private static final int MAX_BUFFER_SIZE=1024;
public static final String STATUSES[]={"Downloading","Paused","Complete","Canceled","Error"};

public static final int DOWNLOADING=0;
public static final int PAUSED=1;
public static final int COMPLETE=2;
public static final int CANCELED=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 int getSize()
{
return size;
}
public float getProgress()
{
return ((float)downloaded/size)*100;
}
public int getStatus()
{
return status;
}
public void pause()
{
status=PAUSED;
stateChanged();
}
public void resume()
{
status=DOWNLOADING;
stateChanged();
download();
}
public void cancel()
{
status = CANCELED;
stateChanged();
}
private void error()
{
status=ERROR;
stateChanged();
}
private void download()
{
Thread thread = new Thread(this);
thread.start();
}
private String getFileName(URL url)
{
String fileName = url.getFile();
return fileName.substring(fileName.lastIndexOf('/')+1);
}
public void run()
{
RandomAccessFile file=null;
InputStream stream=null;
try
{
HttpURLConnection connection=(HttpURLConnection)url.openConnection();
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();
}
file = new RandomAccessFile(getFileName(url),"rw");
file.seek(downloaded);

stream = connection.getInputStream();
while(status==DOWNLOADING)
{
byte buffer[];
if(size-downloaded>MAX_BUFFER_SIZE)
{
buffer =new byte[MAX_BUFFER_SIZE];
}
else
{
buffer =new byte[size - downloaded];
}
int read = stream.read(buffer);
if(read ==-1)
break;
file.write(buffer,0,read);
downloaded += read;
stateChanged();
}
if(status==DOWNLOADING)
{
status=COMPLETE;
stateChanged();
}
}
catch(Exception e)
{
error();
}
finally
{
if(file != null)
{
try
{
file.close();
}
catch(Exception e){}
}
if(stream != null)
{
try
{
stream.close();
}
catch(Exception e)
{}
}
}
}
private void stateChanged()
{
setChanged();
notifyObservers();
}
}