以编程方式将/system/app/*.apk复制到sdcard

我有一个apk的路径“/system/app/Gallery2.apk”,我想把它复制到SD卡上。我实现复制方法

 public void copy(File src, File dst) throws IOException {
    InputStream in = new FileInputStream(src);
    OutputStream out = new FileOutputStream(dst);

    // Transfer bytes from in to out
    byte[] buf = new byte[1024];
    int len;
    while ((len = in.read(buf)) > 0) {
        out.write(buf, 0, len);
    }
    in.close();
    out.close();
}

但它显示IOException

我传递值

 try {
                    File file =new File( pm.getApplicationInfo(TAG_PACKAGE.get(position),PackageManager.GET_META_DATA).publicSourceDir);

                    Toast.makeText(MainActivity.this , pm.getApplicationInfo(TAG_PACKAGE.get(position),PackageManager.GET_META_DATA).publicSourceDir, Toast.LENGTH_LONG).show();

                try {
                    File dir = new File(Environment.getExternalStorageDirectory() + "/foldername/");
                     if(!dir.exists())
                        {
                            if(dir.mkdir()) ;//directory is created;
                            Toast.makeText(MainActivity.this ,dir.toString(), Toast.LENGTH_LONG).show();

                        }

                     copy(file.getAbsoluteFile(), dir);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                } catch (NameNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

例外情况:

  exception java.io.FileNotFoundException: /storage/sdcard0/folder: open failed: EISDIR (Is a directory)

它不起作用,thnks