java Cannot get a STRING value from a NUMERIC cell 错误

一、Cannot get a STRING value from a NUMERIC cell 错误是什么？

使用Apache-POI读取excel文件时，如果获取数据的方法与实际类型不符，会抛出IllegalStateException错误，如下：
java.lang.IllegalStateException: Cannot get a STRING value from a NUMERIC cell
at org.apache.poi.xssf.usermodel.XSSFCell.typeMismatch(XSSFCell.java:1075)
at org.apache.poi.xssf.usermodel.XSSFCell.getRichStringCellValue(XSSFCell.java:396)
at org.apache.poi.xssf.usermodel.XSSFCell.getStringCellValue(XSSFCell.java:348)
at com.fr.function.POIExcel.createDownload(POIExcel.java:95)
at com.fr.function.POIExcel.run(POIExcel.java:30)
at com.fr.script.AbstractFunction.evalExpression(Unknown Source)
at com.fr.parser.FunctionCall.eval(Unknown Source)
at com.fr.script.Calculator.eval(Unknown Source)
at com.fr.stable.script.Expression.eval(Unknown Source)
at com.fr.script.Calculator.evalString(Unknown Source)
at com.fr.script.Calculator.eval(Unknown Source)
at com.fr.script.Calculator.evalValue(Unknown Source)
at com.fr.stable.AbstractFormulaProvider.evalValue(Unknown Source)
at com.fr.report.core.A.J.A(Unknown Source)
at com.fr.report.core.A.J.dealWithBENormal(Unknown Source)
at com.fr.report.core.A.m.cc_ce_array(Unknown Source)
at com.fr.report.core.A.J.A(Unknown Source)
at com.fr.report.core.A.J.A(Unknown Source)
at com.fr.report.core.A.J.A(Unknown Source)
at com.fr.report.core.A.J.A(Unknown Source)
at com.fr.report.core.A.J.A(Unknown Source)
at com.fr.report.core.A.J.C(Unknown Source)
at com.fr.report.core.A.J.execute4Expand(Unknown Source)
at com.fr.report.core.A.J.execute(Unknown Source)
at com.fr.report.worksheet.WorkSheet.execute(Unknown Source)
at com.fr.report.core.sheet.AbstractWorkBookExecutor._execute(Unknown Source)
at com.fr.report.core.sheet.AbstractWorkBookExecutor.execute(Unknown Source)
at com.fr.main.impl.WorkBook.execute(Unknown Source)
at com.fr.main.impl.WorkBook.execute(Unknown Source)
at com.fr.web.cache.ReportCache.getResultWorkBook(Unknown Source)
at com.fr.stable.PageActor.getResultBookFromCacheIfNeed(Unknown Source)
at com.fr.main.impl.WorkBookTemplateDelegate.execute(Unknown Source)
at com.fr.web.core.ReportSessionIDInfor.execute(Unknown Source)
at com.fr.web.core.ReportSessionIDInfor.computeBook2Show o r