docs.sheetjs.com/docz/static/nashorn/SheetJSNashorn.java

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.Scanner;

public class SheetJSNashorn {
  public static void main(String[] args) throws Exception {
    /* initialize */
    ScriptEngine engine = (new ScriptEngineManager()).getEngineByName("javascript");

    /* read script file */
    engine.eval("var global = (function(){ return this; }).call(null);");
    engine.eval(new Scanner(SheetJSNashorn.class.getResourceAsStream("/shim.min.js")).useDelimiter("\\Z").next());
    engine.eval(new Scanner(SheetJSNashorn.class.getResourceAsStream("/xlsx.full.min.js")).useDelimiter("\\Z").next());
    engine.eval("print('SheetJS Version ' + XLSX.version);");

    /* read spreadsheet bytes */
    engine.put("bytes", Files.readAllBytes(Paths.get(args[0])));

    /* convert signed byte array to JS Uint8Array or unsigned byte array */
    engine.eval("function b2a(b) {" +
      "var out = typeof Uint8Array == 'function' ? new Uint8Array(b.length) : new Array(b.length);" +
      "for(var i = 0; i < out.length; i++) out[i] = b[i] & 0xFF;" +
      "return out;" +
    "}" +
    "var u8a = b2a(bytes)");

    /* parse workbook */
    engine.eval("var wb = XLSX.read(u8a, {type: 'array'})");

    /* get first worksheet as CSV */
    engine.eval("var ws = wb.Sheets[wb.SheetNames[0]];");
    Object res = engine.eval("XLSX.utils.sheet_to_csv(ws)");
    System.out.println(res);
  }
}