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新建下载任务对话框的设计主要是根据JFace中Dialog设计实现，如图7所示： http://www.paper51.com copyright paper51.com 图7 新建下载任务对话框 内容来自论文无忧网 www.paper51.com 从对话框中可以看到下载任务的三个主要参数：URL地址、存储目录、以及选择下载线程数，在信息填写完毕后按下确定按钮就会对NewHttpTask建立实例开始进行下载。同时在点击浏览按钮时会弹出浏览目录对话框，如图8所示： copyright paper51.com paper51.com 图8 浏览对话框 内容来自论文无忧网 www.paper51.com
以下是对话框的设计实现核心代码： http://www.paper51.com protected ControlcreateDialogArea(Composite parent) { copyright paper51.com Composite composite = (Composite)super.createDialogArea(parent); paper51.com Composite panel = new Composite(composite, SWT.None); copyright paper51.com
GridData panelData = new GridData(SWT.FILL, SWT.FILL, true, true); copyright paper51.com panel.setLayoutData(panelData); http://www.paper51.com panel.setLayout(new GridLayout(5, false)); paper51.com
new Label(panel, SWT.RIGHT).setText("存储目录："); 内容来自www.paper51.com
btnBrowse.setText("浏览"); copyright paper51.com btnBrowse.addSelectionListener(new SelectionAdapter(){ paper51.com public void widgetSelected(SelectionEvent e){ 内容来自www.paper51.com final Shell shell = Display.getCurrent().getActiveShell(); paper51.com DirectoryDialog dlg = new DirectoryDialog(shell); copyright paper51.com dlg.setText("浏览文件夹"); 内容来自www.paper51.com
dlg.setMessage("请选择一个目录："); paper51.com
dlg.setFilterPath("c:/download"); paper51.com String dir = dlg.open(); 内容来自www.paper51.com if (dir != null) { 内容来自www.paper51.com
NewTaskDialog.this.cmbDestFolders.add(dir); paper51.com NewTaskDialog.this.cmbDestFolders.select(0); paper51.com
} copyright paper51.com
} paper51.com }); paper51.com new Label(panel,SWT.NONE).setText("选择下载线程数"); copyright paper51.com cmbThreadCounts = new Combo(panel, SWT.READ_ONLY); http://www.paper51.com return panel；} copyright paper51.com
protected voidcreateButtonsForButtonBar(Composite parent) { paper51.com
createButton(parent, IDialogConstants.OK_ID, "确定", true); copyright paper51.com createButton(parent, IDialogConstants.CANCEL_ID, "取消", false); http://www.paper51.com } copyright paper51.com 下载功能的实现主要原理是： paper51.com l 判断NewHttpTask构造函数中参数是否合法； paper51.com
l 然后通过使用HttpClient包，建立HTTP连接； paper51.com l 通过Head方法得到相应文件的长度信息； 内容来自www.paper51.com l 判断是否支持多线程下载； 内容来自论文无忧网 www.paper51.com l 通过判断状态码（Status Code）判断是否有异常或者文件是全部下载还是部分下载，也就是文件是第一次下载还是有过停止后继续下载。 http://www.paper51.com l 根据下载线程数把文件分块； 内容来自论文无忧网 www.paper51.com l 建立相应线程进行下载，并读入； 内容来自www.paper51.com l 将读到的数据写到指定路径； paper51.com 核心代码如下： 内容来自论文无忧网 www.paper51.com
//建立连接 copyright paper51.com MultiThreadedHttpConnectionManagerconnectionManager = copyright paper51.com new MultiThreadedHttpConnectionManager(); http://www.paper51.com
connectionManager.getParams().setDefaultMaxConnectionsPerHost(20); http://www.paper51.com httpClient = new HttpClient(connectionManager); http://www.paper51.com //得到文件大小 内容来自论文无忧网 www.paper51.com
HeadMethod head = new HeadMethod(url.toString()); 内容来自论文无忧网 www.paper51.com head.setFollowRedirects(false); paper51.com
int statusCode = httpClient.executeMethod(head); 内容来自论文无忧网 www.paper51.com //判断资源是否支持多线程下载 paper51.com if (statusCode ==HttpStatus.SC_MOVED_TEMPORARILY){ 内容来自www.paper51.com String recentUrl =head.getResponseHeader("Location").getValue(); 内容来自www.paper51.com logger.info("URL redirection: " +recentUrl); 内容来自论文无忧网 www.paper51.com this.url = new URL(url.getProtocol(), paper51.com url.getHost(), paper51.com url.getPort(), 内容来自www.paper51.com recentUrl); paper51.com head = new HeadMethod(url.toString()); 内容来自www.paper51.com statusCode =httpClient.executeMethod(head); 内容来自www.paper51.com //将文件分块，并建立相应线程完成下载 copyright paper51.com
contentLength = getResourceContentLen(); 内容来自论文无忧网 www.paper51.com msg = "Resource Content Length is " +contentLength; 内容来自www.paper51.com logger.info(msg); 内容来自www.paper51.com listener.onProgress(msg); paper51.com
listener.onGetContentLength(destination.getName(),contentLength); http://www.paper51.com
long chunk = contentLength / threadCounts; http://www.paper51.com long startPos = 0; 内容来自论文无忧网 www.paper51.com long endPos; paper51.com for (int i = 0; i < threadCounts; i++) copyright paper51.com {ndPos = startPos + chunk; http://www.paper51.com if (i == threadCounts - 1) http://www.paper51.com {endPos = contentLength;} http://www.paper51.com workers[i] = new HttpTaskWorker( 内容来自论文无忧网 www.paper51.com "Worker Thread #" + (i + 1), http://www.paper51.com startPos, endPos - 1); 内容来自www.paper51.com workers[i].start(); copyright paper51.com
startPos = endPos; copyright paper51.com //存储文件 内容来自www.paper51.com destination = new File(destination, paper51.com new File(url.getPath()).getName()); 内容来自论文无忧网 www.paper51.com store = new RandomAccessFile(destination,"rw"); http://www.paper51.com 另外，由于在新建任务栏中需要填入下载资源地址URL，而URL地址经常是一串很长的字符串，每次都手工复制、粘贴到下载软件任务栏中显然非常麻烦。为了用户使用更加的方便，下载软件在新建任务时支持将系统剪贴板中的内容（URL地址）自动添加到新建任务中的URL地址栏中，这样就意味着用户在粘贴地址后再打开新建下载任务时，ULR地址已经被填在新建任务中的URL地址栏。这样可以大大节省用户的工作量。主要代码如下： copyright paper51.com
protected String getClipBoardURL() { paper51.com Clipboard clipboard = newClipboard(Display.getCurrent()); copyright paper51.com TextTransfer textTransfer =TextTransfer.getInstance(); http://www.paper51.com
String textData =(String)clipboard.getContents(textTransfer); 内容来自论文无忧网 www.paper51.com URL url; http://www.paper51.com try { http://www.paper51.com url = new URL(textData); 内容来自www.paper51.com if(url.getProtocol().equals("http")) http://www.paper51.com
return textData;} paper51.com catch(MalformedURLException e) { 内容来自www.paper51.com
} paper51.com return ""; http://www.paper51.com
} http://www.paper51.com |