eclipse已在构建路径导入poi包，代码编译正常，但运行时提示没有发现类，请求解决方案，初学者衷心感谢！

Question

eclipse已在构建路径导入poi包，代码编译正常，但运行时提示没有发现类
代码如下：

import java.io.File;
import java.io.IOException;
import java.io.FileOutputStream;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFRow;

public class Excel {
    public static void main(String[] args) throws IOException {
        HSSFWorkbook workbook = new HSSFWorkbook();
        HSSFSheet sheet = workbook.createSheet("poiTest");
        for (int row = 0; row <= 10; row++) {
            HSSFRow rows = sheet.createRow(row);
            for (int col = 0; col <= 10; col++) {
                rows.createCell(col).setCellValue("数据:第" + row + "行，第" + col + "列");
            }
        }
        File xlsFile = new File("C:\\Users\\lihh\\Desktop\\poi.xls");
        FileOutputStream xlsStream = new FileOutputStream(xlsFile);
        workbook.write(xlsStream);
        workbook.close();
    }
}

报错如下：
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/poi/hssf/usermodel/HSSFWorkbook
at Excel.main(Excel.java:10)
Caused by: java.lang.ClassNotFoundException: org.apache.poi.hssf.usermodel.HSSFWorkbook
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:606)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:168)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
1 more
截图如下：

请求解决方案，初学者衷心感谢！

Answer 1

检查你的项目下的lib文件里的jar包，然后去看看Web App Libraries下面有没有对应的jar，如果发现没有，就对lib文件夹下对应的jar进行右键 build path-->add to build path