download.java

HTTP单线程下载实例

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[] = {"下载中...", "暂停", "已完成", "取消", "错误"};   
	
	//状态标志码 
	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;   
		//开始下载
		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 = CANCELLED;   
		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){
					e.printStackTrace();
				}   
			}   
			if (stream != null) {   
				try {   
					stream.close();   
				} catch (Exception e) {
				e.printStackTrace();
				}   
			}   
		}   
	}     
	
	private void stateChanged(){   
		setChanged();   
		notifyObservers();   
	}   
}