You can use the JDBC API to connect to the Oracle database and read data from it.
There are a number of ways to handle Excel files in Java. Since the XLS file format is a proprietary Microsoft format, there is no official support for XLS files in Java. There are libraries which you can use to read and write XLS files such as Apache POI.
You could also make it easier for yourself by writing a simple CSV (comma separated values) file instead of an XLS file. Excel can read CSV files easily.