/* my test code */

public class TestPOI {

	public static void main(String[] args) throws Exception {
		try (InputStream in = new FileInputStream("d:/tmp/TEST.xlsx")) {
			XSSFWorkbook workbook = new XSSFWorkbook(in);
			CTDefinedNames definedNames = workbook.getCTWorkbook().getDefinedNames();
			List<CTDefinedName> definedNameList = definedNames.getDefinedNameList();
			for (CTDefinedName defName : definedNameList) {
				System.out.println(defName.getName() + ": " + defName.getStringValue());
			}
		}
	}

}

/* result when calling definedNames.getDefinedNameList() */

Exception in thread "main" java.lang.NoClassDefFoundError: org/openxmlformats/schemas/spreadsheetml/x2006/main/impl/CTDefinedNamesImpl$1DefinedNameList
	at org.openxmlformats.schemas.spreadsheetml.x2006.main.impl.CTDefinedNamesImpl.getDefinedNameList(Unknown Source)
	at test.poi.TestPOI.main(TestPOI.java:25)
Caused by: java.lang.ClassNotFoundException: org.openxmlformats.schemas.spreadsheetml.x2006.main.impl.CTDefinedNamesImpl$1DefinedNameList
	at java.net.URLClassLoader$1.run(URLClassLoader.java:366)