从jsp调用Java方法

Question

I am calling my java method from jsp its giving NoClassDefFoundError: error .

But my method is working when i am calling from the main method. i have used xlrd jar in my code and i have placed the jar lib folder as well. but still it gives error.

Exception trace :

org.apache.jasper.JasperException: An exception occurred processing JSP page /exportDSD.jsp at line 20

17:     //excel.getExcel();
18:     
19:     Report r = new Report();
20:     r.generateReport();
21:     
22:     System.out.println("Generated DSD");
23: %> 

Stacktrace :

org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

root cause :

javax.servlet.ServletException: java.lang.NoClassDefFoundError: xlrd/Workbook
    org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:916)
    org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:845)
    org.apache.jsp.exportDSD_jsp._jspService(exportDSD_jsp.java:107)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

My code :

import org.apache.poi.hssf.usermodel.HSSFCell; 
 import org.apache.poi.hssf.usermodel.HSSFCellStyle; 
 import org.apache.poi.hssf.usermodel.HSSFDataFormat; 
 import org.apache.poi.hssf.usermodel.HSSFRow; 
 import org.apache.poi.hssf.usermodel.HSSFSheet; 
 import org.apache.poi.hssf.usermodel.HSSFWorkbook; 
 import xlrd.*;

 public void generateReport() throws BiffException, ClassNotFoundException, SQLException, IOException { 
 ... ... 
 } 

From jsp i am calling like this:

<% Report r =new Report(); r.generateReport(); %>

Answer 1

Appears JSP import not correct:

Add jar in WEB-INF/lib
Add <%@ page import="xlrd.*" %> to the top of your JSP

To import more than one classes, use the following format:

<%@ page import="com.sample.Report,xlrd.*" %>

Answer 2

The issue is with jar containing Workbook in some jar. Put it in the WEB-INF/lib folder. I don't think, this need to be included in the JSP as well.

Answer 3

NoClassDefFoundError is a JVM Error which means that JVM or class loader was not able to load the class definition . This means that class was found but due to some reason JVM or class loader was not able to load the class definition.
java.lang.NoClassDefFoundError: xlrd/Workbook doesn't mean that class was not found, if that was the case you would have got ClassNotFoundException . On contrary, class file was found but JVM is unable to load the class definition.

For NoClassDefFoundError you can check source of xlrd/Workbook if it contains some static block or member which is referencing some class which is not present or causing issue at runtime.