为应用添加文件读取权限。具体代码示例如下：

在AndroidManifest.xml文件中添加以下权限：

在Java代码中获取Read External Storage权限：

if (ContextCompat.checkSelfPermission(thisActivity,
                Manifest.permission.READ_EXTERNAL_STORAGE)
        != PackageManager.PERMISSION_GRANTED) {

    // Permission is not granted
    // Should we show an explanation?
    if (ActivityCompat.shouldShowRequestPermissionRationale(thisActivity,
            Manifest.permission.READ_EXTERNAL_STORAGE)) {
        // Show an explanation to the user *asynchronously* -- don't block
        // this thread waiting for the user's response! After the user
        // sees the explanation, try again to request the permission.
    } else {
        // No explanation needed; request the permission
        ActivityCompat.requestPermissions(thisActivity,
                new String[]{Manifest.permission.READ_EXTERNAL_STORAGE},
                MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE);

        // MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE is an
        // app-defined int constant. The callback method gets the
        // result of the request.
    }
} else {
    // Permission has already been granted
}

在回调方法中处理权限请求的结果：

@Override
public void onRequestPermissionsResult(int requestCode,
        String[] permissions, int[] grantResults) {
    switch (requestCode) {
        case MY_PERMISSIONS_REQUEST_READ_EXTERNAL_STORAGE: {
            // If request is cancelled, the result arrays are empty.
            if (grantResults.length > 0
                && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                // permission was granted, yay! Do the
                // contacts-related task you need to do.

            } else {

                // permission denied, boo! Disable the
                // functionality that depends on this permission.
            }
            return;
        }

        // other 'case' lines to check for other
        // permissions this app might request.
    }
}