download.java

1.代码全由java书写 2.支持http1.1的可续传下载 3.GUI采用的是Java Swing 4.设计模式为Observer 5.采用了多线程机制

//创建于2007-11-22 by刘浩
//最后更改于2008-01-01 by兰冲
import java.io.*;
import java.net.*;
import java.util.*;

import javax.swing.JOptionPane;
//负责一个具体任务的下载   runable
//本类实现从一个URL下载一个文件,保存到指定路径,并以指定文件名保存的功能
class Download extends Observable implements Runnable {
  // 最大的缓冲区大小
  private static final int MAX_BUFFER_SIZE = 1024;

  // 状态名称
  public static final String STATUSES[] = {"下载",
    "暂停", "完成", "取消", "错误"};

  // 这些是状态编码
  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; // 下载url
  private String dir; //下载文件保存目录	
  private String fileName; //保存文件名
  private String fullFilePath; //文件下载后的完整路径
  private int size; // 下载文件的大小(单位为字节)
  private int downloaded; // 已下载字节数
  private int status; // 当前下载状态

  //Download的构造函数
  public Download(URL url, String dir, String fileName) {
    this.url = url;
    this.dir = dir;
    this.fileName = fileName;
    if (!this.dir.endsWith("\\"))
    	this.dir = this.dir + "\\";
    this.fullFilePath = this.dir + fileName;
    File file = new File(fullFilePath);
    if ( file.exists())
  	{
    	JOptionPane.showMessageDialog(null,
                "待下载文件已存在", "Error",
                JOptionPane.ERROR_MESSAGE);
    	return;
  	}
    else
    {
    	try
    	{
    		file.createNewFile();
    	}
    	catch( IOException e)
    	{
    		JOptionPane.showMessageDialog(null,
                    "创建文件失败", "Error",
                    JOptionPane.ERROR_MESSAGE);
    	}
    }
    
    size = -1;
    downloaded = 0;
    status = DOWNLOADING;

    //开始下载
    download();
  }

  // 返回下载任务的下载地址
  public String getUrl() {
    return url.toString();
  }

  private String getFileName()
  {
	  return fileName;
  }
  
  // 返回下载文件的大小
  public int getSize() {
    return size;
  }

  // 返回下载任务的完成百分比
  public float getProgress() {
    return ((float) downloaded / size) * 100;
  }

  // 返回下载状态码
  public int getStatus() {
    return status;
  }

  // 暂停当前下载
  public void pause() {
    status = PAUSED;
    stateChanged();
  }

  // 恢复当前下载
  public void resume() {
    status = DOWNLOADING;
    stateChanged();
    download();
  }

  // 取消当前下载
  public void cancel() {
    status = CANCELLED;
    stateChanged();
  }

  // 标记当前下载任务发生错误,通知观察者
  private void error() {
    status = ERROR;
    stateChanged();
  }

  // 开始或恢复下载
  private void download() {
    Thread thread = new Thread(this);
    thread.start();
  }

  // 下载文件
  public void run() {
    RandomAccessFile file = null;
    InputStream stream = null;

    try {
      // 打开到URL的连接
      HttpURLConnection connection =
        (HttpURLConnection) url.openConnection();

      // 标明要下载文件的哪个部分
      connection.setRequestProperty("Range",
        "bytes=" + downloaded + "-");

      // 连接到服务器
      connection.connect();

      // 确定连接成功
      if (connection.getResponseCode() / 100 != 2) {
        error();
      }

      // 检查待下载的内容长度
      int contentLength = connection.getContentLength();
      if (contentLength < 1) {
        error();
      }

      /* 如果下载文件的大小没有设定,设置其大小 */
      if (size == -1) {
        size = contentLength;
        stateChanged();
      }

      //打开文件,并将文件读写指针定位到文件末尾
      file = new RandomAccessFile(fullFilePath, "rw");
      file.seek(downloaded);

      stream = connection.getInputStream();
      byte buffer[] = new byte[MAX_BUFFER_SIZE];
      while (status == DOWNLOADING) {
        /* 缓冲字节数组 */
        
        /*if (size - downloaded > MAX_BUFFER_SIZE) {
          buffer = new byte[MAX_BUFFER_SIZE];
        } else {
          buffer = new byte[size - downloaded];
        }*/

        // 从服务器读数据到缓冲中
        int read = stream.read(buffer);
        
        if (read == -1)
          break;

        // 将缓冲写到文件中
        file.write(buffer, 0, read);
        downloaded += read;
        stateChanged();
      }

      /* 当执行到这里时设置下载任务的状态为已完成 */
      if (status == DOWNLOADING) {
        status = COMPLETE;
        stateChanged();
      }
    } catch (Exception e) {
      error();
    } finally {
      // 关闭文件
      if (file != null) {
        try {
          file.close();
        } catch (Exception e) {}
      }

      // 关闭到服务器的连接
      if (stream != null) {
        try {
          stream.close();
        } catch (Exception e) {}
      }
    }
  }

  // 通知observers本download的状态已经改变.
  private void stateChanged() {
    setChanged();
    notifyObservers();
  }
}