很多时候Uri.getPath();并不起作用，所以我们需要通过特殊的方式去解决，源代码如下（有参考，但实测过）：

public static String getPhotoPathFromContentUri(Context context, Uri uri) {
    String photoPath = "";
    if (context == null || uri == null) {
        return photoPath;
    }

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT && DocumentsContract.isDocumentUri(context, uri)) {
        String docId = DocumentsContract.getDocumentId(uri);
        if (isExternalStorageDocument(uri)) {
            String[] split = docId.split(":");
            if (split.length >= 2) {
                String type = split[0];
                if ("primary".equalsIgnoreCase(type)) {
                    photoPath = Environment.getExternalStorageDirectory() + "/" + split[1];
                }
            }
        } else if (isDownloadsDocument(uri)) {
            Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"), Long.valueOf(docId));
            photoPath = getDataColumn(context, contentUri, null, null);
        } else if (isMediaDocument(uri)) {
            String[] split = docId.split(":");
            if (split.length >= 2) {
                String type = split[0];
                Uri contentUris = null;
                if ("image".equals(type)) {
                    contentUris = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
                } else if ("video".equals(type)) {
                    contentUris = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
                } else if ("audio".equals(type)) {
                    contentUris = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
                }
                String selection = MediaStore.Images.Media._ID + "=?";
                String[] selectionArgs = new String[]{split[1]};
                photoPath = getDataColumn(context, contentUris, selection, selectionArgs);
            }
        }
    } else if ("file".equalsIgnoreCase(uri.getScheme())) {
        photoPath = uri.getPath();
    } else {
        photoPath = getDataColumn(context, uri, null, null);
    }

    return photoPath;
}

private static boolean isExternalStorageDocument(Uri uri) {
    return "com.android.externalstorage.documents".equals(uri.getAuthority());
}

private static boolean isDownloadsDocument(Uri uri) {
    return "com.android.providers.downloads.documents".equals(uri.getAuthority());
}

private static boolean isMediaDocument(Uri uri) {
    return "com.android.providers.media.documents".equals(uri.getAuthority());
}

private static String getDataColumn(Context context, Uri uri, String selection, String[] selectionArgs) {
    Cursor cursor = null;
    String column = MediaStore.Images.Media.DATA;
    String[] projection = {column};
    try {
        cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs, null);
        if (cursor != null && cursor.moveToFirst()) {
            int index = cursor.getColumnIndexOrThrow(column);
            return cursor.getString(index);
        }
    } finally {
        if (cursor != null && !cursor.isClosed()) {
            cursor.close();
        }
    }
    return null;
}