大家进来帮我看看这些异常怎么解决？

[javac] import jxl.Cell;
  [javac] ^
  [javac] D:\myinformation\im_gysyz\tmp\ZPersonInfoServlet.java:15: package jxl does not exist
  [javac] import jxl.Sheet;
  [javac] ^
  [javac] D:\myinformation\im_gysyz\tmp\ZPersonInfoServlet.java:16: package jxl does not exist
  [javac] import jxl.Workbook;
  [javac] ^
  [javac] D:\myinformation\im_gysyz\tmp\ZPersonInfoServlet.java:270: cannot resolve symbol
  [javac] symbol : class Workbook
  [javac] location: class tw.com.sinews.im.impl.ZPersonInfoServlet
  [javac] Workbook book=Workbook.getWorkbook(file);
  [javac] ^
  [javac] D:\myinformation\im_gysyz\tmp\ZPersonInfoServlet.java:270: cannot resolve symbol
  [javac] symbol : variable Workbook
  [javac] location: class tw.com.sinews.im.impl.ZPersonInfoServlet
  [javac] Workbook book=Workbook.getWorkbook(file);
  [javac] ^
  [javac] D:\myinformation\im_gysyz\tmp\ZPersonInfoServlet.java:271: cannot resolve symbol
  [javac] symbol : class Sheet
  [javac] location: class tw.com.sinews.im.impl.ZPersonInfoServlet
  [javac] Sheet[] sheet=book.getSheets();
  [javac] ^
  [javac] D:\myinformation\im_gysyz\tmp\ZPersonInfoServlet.java:280: cannot resolve symbol
  [javac] symbol : class Cell
  [javac] location: class tw.com.sinews.im.impl.ZPersonInfoServlet
  [javac] Cell[] cells=sheet[sheetCount].getRow(rowNum);
  [javac] ^
  [javac] 7 errors
我只要用到这些类就会编译出错。我在网上下载的jxl.jar导入到项目里去，
导进去的jar包是对的，在public static void main 里面测试通过，可是编译项目的时候出现以上错误，只要导入jxl里的Cell、Sheet、Workbook 就会出现以上的编译错误。