java IO 下載

這幾天因爲項目需要，寫一個通過文件流下載文件的東西。整個過程需要一個後臺服務器和一個GUI的程序，GUI做下載操作。

URLConnection conn = url.openConnection();  
	         int contentLength = conn.getContentLength();
	         System.out.println("########## length = " + contentLength);
	         InputStream inStream = conn.getInputStream();  
	         FileOutputStream fs = new FileOutputStream(saveFile);  
	  
	         byte[] buffer = new byte[10240];  
	         while ((byteread = inStream.read(buffer)) != -1) {  
	               bytesum += byteread;                 
	               System.out.print(bytesum);  
	               fs.write(buffer, 0, byteread);
	               long downloadPercent = bytesum * 100 / contentLength  ;
	               MainClass.dwProgressBar.setValue((int)downloadPercent);  //進度值
	               System.out.println(" ; percents: " + downloadPercent);  
	          }
	         fs.close();

GUI端的下載便做好了。

String filePath = getServletContext().getRealPath(File.separator) + "mptd" + File.separator + path
				+ File.separator + sName + File.separator;
		System.out.println(filePath);
		String fileName = new File(filePath).list()[0];
		
		File file = new File(filePath + fileName);
		
		
		System.out.println(file.getAbsolutePath());
		System.out.println(file.isFile());
		
		FileInputStream fis = new FileInputStream(file);
		PrintWriter out = response.getWriter();
		
		int b = 0;
		while ((b = fis.read()) != -1) {
			out.write(b);
		}
		
		response.setHeader("Content-Disposition","attachment;filename=\"" + URLEncoder.encode(fileName,"utf-8") + "\"");
		response.setHeader("Content-Length","" + file.length());
		
		fis.close();
		out.close();

服務器端的下載代碼也就這樣。

好了，我們可以愉快的玩耍了

...

咦，怎麼回事兒？下載不動啊，GUI客戶端下載，文件長度爲-1，下載進度一直都爲負數。

折騰半天，原來問題在服務器端的這兩句話：

response.setHeader("Content-Disposition","attachment;filename=\"" + URLEncoder.encode(fileName,"utf-8") + "\"");
		response.setHeader("Content-Length","" + file.length());

這兩句話一定要放在文件讀寫之前，放在讀寫之後就不起作用了。所以改成下面這樣就好了：

String filePath = getServletContext().getRealPath(File.separator) + "mptd" + File.separator + path
				+ File.separator + sName + File.separator;
		System.out.println(filePath);
		String fileName = new File(filePath).list()[0];
		
		File file = new File(filePath + fileName);

		response.setHeader("Content-Disposition","attachment;filename=\"" + URLEncoder.encode(fileName,"utf-8") + "\"");
		response.setHeader("Content-Length","" + file.length());
		
		System.out.println(file.getAbsolutePath());
		System.out.println(file.isFile());
		
		FileInputStream fis = new FileInputStream(file);
		PrintWriter out = response.getWriter();
		
		int b = 0;
		while ((b = fis.read()) != -1) {
			out.write(b);
		}
		
		fis.close();
		out.close();

好了，現在真的可以愉快的玩耍了。