如果在android中重命名为不同的文件扩展名，如何获取实际的文件类型？

import android.webkit.MimeTypeMap;

String fileName = "example.txt";
String fileExtension = fileName.substring(fileName.lastIndexOf(".") + 1);

String mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(fileExtension.toLowerCase());

import android.webkit.MimeTypeMap;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        String fileName = "example.txt";
        String fileExtension = fileName.substring(fileName.lastIndexOf(".") + 1);
        String mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(fileExtension.toLowerCase());

        if (mimeType != null) {
            Log.d("File Type", mimeType);
        } else {
            Log.d("File Type", "Unknown");
        }
    }
}