Exception in thread main javalangNoClassDefFoundError orgapachecommonsiooutputUnsynchronizedByteArrayOutputStream at orgapachepoipoifsfilesystemFileMagicvalueOfFileMagicjava209 at orgapachepoissusermo

This error is caused by a missing or incorrect version of the Apache Commons IO library. The class "UnsynchronizedByteArrayOutputStream" is part of this library and is required by the Apache POI library to read Excel files.

To fix this error, you can download the correct version of the Commons IO library and add it to your project's classpath. Alternatively, you can use a build tool like Maven or Gradle to manage your dependencies and automatically download the required libraries.