在Android的本地内存中保存pdf文件

我试图从Android项目中的URL保存一个pdf文件，但是当它保存.pdf文件时，它的维度是0KB。代码创建了目录和PDF文件Ciao.PDF，我还拥有在我的AndroidManifest.xml中的INTERNET和WRITE_EXTERNAL_存储权限。 代码如下：

        LinkTo = "http://www.ancestralauthor.com/download/sample.pdf";
        Toast.makeText(getApplicationContext(),LinkTo, Toast.LENGTH_LONG).show();
        String storage = Environment.getExternalStorageState();
        Log.i("System out", "" + storage);
        File rootsd = Environment.getExternalStorageDirectory();
        Log.d("ROOT PATH", "" + rootsd.getAbsolutePath());
        File mydir = new File(rootsd.toString() + "/unplugger");
        Log.i("DIR PATH", "" + mydir.getAbsolutePath());
        mydir.mkdir();
        URL u;
        try {
            u = new URL(LinkTo);

            HttpURLConnection c = (HttpURLConnection) u.openConnection();
            c.setRequestMethod("GET");
            c.setDoOutput(true);
            c.connect();
            FileOutputStream f = new FileOutputStream(new File(mydir + "/"
                    + "Ciao.pdf"));

            InputStream input = c.getInputStream();

            byte[] buffer = new byte[1024];
            int len1 = 0;
            while ((len1 = input.read(buffer)) > 0) {
                f.write(buffer, 0, len1);
                f.flush();
            }
            f.close();
            c.disconnect();
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            Log.i("System out","malformed :"+e.getMessage());
            Log.i("System out","malformed :"+e.toString());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            Log.i("System out","io: "+e.getMessage());
            Log.i("System out","io: "+e.toString());
        }

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把f.冲洗；while循环之后。@user370305完成，同样的错误