unable to create directory in external storage

问题

I wanted to the application to create a new directory to store downloaded image inside sdcard. I tried a few methods but still I can't seems to get it work. I included permission for External Storage in android manifest as well. Any comments will be appreciated.

        Bitmap bm = null;
        InputStream in;
            in = new java.net.URL("http://blogs.computerworld.com/sites/computerworld.com/files/u177/google-nexus-4.jpg").openStream();
            bm = BitmapFactory.decodeStream(new PatchInputStream(in));
            File file = new File(Environment.getExternalStorageDirectory() + "/map");
            file.mkdirs();
            File outputFile = new File(file, "Image"+NumIncrease);
            FileOutputStream fos = new FileOutputStream(outputFile);

Below is what I get from running this.

12-05 15:55:25.566: D/skia(4244): ---- read threw an exception
12-05 15:55:25.585: D/skia(4244): ---- read threw an exception
12-05 15:55:25.585: W/System.err(4244): java.io.IOException: Is a directory
12-05 15:55:25.585: W/System.err(4244):     at org.apache.harmony.luni.platform.OSFileSystem.read(Native Method)
12-05 15:55:25.585: W/System.err(4244):     at dalvik.system.BlockGuard$WrappedFileSystem.read(BlockGuard.java:165)
12-05 15:55:25.585: W/System.err(4244):     at java.io.FileInputStream.read(FileInputStream.java:290)
12-05 15:55:25.585: W/System.err(4244):     at java.io.BufferedInputStream.fillbuf(BufferedInputStream.java:166)
12-05 15:55:25.863: E/MediaStore(4244): Failed to create thumbnail, removing original

EDIT Below is how I handle the bitmap.

bm.compress(Bitmap.CompressFormat.JPEG, 85, fos);

回答1:

Following points may help you

Probably exception is thrown because there is no MediaCard subdir. You should check if all dirs in the path exist.
Add the permissions in the manifest for this to work..
You should never use "/sdcard/" as a constant, because manufacturers may decide to mount the SD-Card to another path. Always use Environment.getExternalStorageDirectory(); instead.