Java I/O help. Jar Cannot Open File: URI is Not Hierarchal - maven

Question

I have been searching for 3 days now nonstop looking at every post I can find. My program runs on IntelliJ, but cannot run on an executable. Your help would be appreciated :)
More importantly, where can I find a in depth user-friendly tutorial? Is there a course or book I can pay for? On Udemy, the java classes completely fail to mention I/O such as classpath and URI. TutorialsPoint briefly goes over I/O buts its not indepth. Did I miss something? Is there an easier way to do all this??
Similar posts that have not worked for me:
Java Jar file: use resource errors: URI is not hierarchical
https://stackoverflow.com/a/27149287/155167
I am trying to load an excel file. I am using Maven. Apache POI says it needs a File. So InputStream does not work. http://poi.apache.org/components/spreadsheet/quick-guide.html#FileInputStream
When I java -jar jarFile, it gives me the error:
C:\Users\1010\Documents\Personal\MonsterManager>java -jar monsterManagerVer3.jar
Exception in thread "main" java.lang.IllegalArgumentException: URI is not hierarchical
at java.base/java.io.File.<init>(File.java:421)
at LoadExcel.<init>(LoadExcel.java:62)
at monsterRunner.<init>(monsterRunner.java:13)
at monsterRunner.main(monsterRunner.java:24)
Here is the code
public LoadExcel() throws IOException, URISyntaxException, InvalidFormatException {
mNames = null;
URL ins = this.getClass().getResource("/excel_List.xlsx");
if (ins == null)
throw new FileNotFoundException("The XLSX file didn't exist on the classpath");
ins.toString().replace(" ","%20"); //<-Runs without this part
File file = new File(ins.toURI()); //this is line 62
// File f = new File(getClass().getResource("/MyResource").toExternalForm());
//String path = this.getClass().getClassLoader().getResource("/excel_List.xlsx").toExternalForm();
//File file = new File(path);
OPCPackage pkg = OPCPackage.open(file);
XSSFWorkbook wb = new XSSFWorkbook(pkg);
//FileInputStream fis=new FileInputStream(new File(excelFile));
// XSSFWorkbook wb = new XSSFWorkbook(fis);
XSSFSheet sheet = wb.getSheetAt(0);
loadExcel(sheet);
cacheNames();
// fis.close();
wb.close();
}
If it helps here is the path to the excel file:
src\main\resources\excel_List.xlsx
UPDATE:
so I took the excel file out of the resources folder
\nameOfMyProgram\excel_List.xlsx
and now I get this error.
I tried several versions of using the classLoader, Class and Thread to solve this error from Different ways of loading a file as an InputStream
but I still cannot get it to compile.
Error and my code

Answer 1

If you have to use File object do not put xls-file into resources directory.
Maven puts all files from resources directory into jar.
Java can not create File object based on file in jar-file.
Put your xls-file somewhere in file system and create File object based on its URL.
Since your xls-file is not a resource do not use getResource.
Its URL is its full filename (with path).

Answer 2

This code below works with jar executable
String path = new File("excel_List.xlsx").getAbsoluteFile().toString();
File file = new File(path);
if(!file.exists()){
JOptionPane.showMessageDialog(null,"File not found!");
System.exit(0);
}
OPCPackage pkg = OPCPackage.open(file);
XSSFWorkbook wb = new XSSFWorkbook(pkg);