Error in struts with collection classes

Question

Hi All,
I have tried to list all the employee through dabase search i have created with strus logic tag in search.jsp page
as following
<bean:size id="size" name="searchForm" property="results"/>
<logic:equal name="size" value="0">
<center><font color="red"><b>No Employees Found</b></font></center>
</logic:equal>
<logic:greaterThan name="size" value="0">
<table border="1">
<tr>
<th>Name</th>
<th>Social Security Number</th>
</tr>
<logic:iterate id="result" name="searchForm" property="results">
<tr><td><bean:write name="result" property="name"/></td>
<td><bean:write name="result" property="ssNum"/></td>
</tr>
</logic:iterate>
</table>
</logic:greaterThan>
</logic:present>
2. The following class shows ActionServlet as SearchAction.java class
public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request,HttpServletResponse response)
throws Exception
EmployeeSearchService service = new EmployeeSearchService();
List results=new ArrayList();;
SearchForm searchForm = (SearchForm) form;
// Perform employee search based on what criteria was entered.
String name = searchForm.getName();
if (name != null && name.trim().length() > 0)
results = service.searchByName(name);
/* else {
results = service.searchBySsNum(searchForm.getSsNum().trim());
// Place search results in SearchForm for access by JSP.
searchForm.setResults(results);
// Forward control to this Action's input page.
return mapping.getInputForward();
3. The following class created for search the employee as EmployeeSearchService.java
Note: This file will implement EmployeeDB.java for database connections and also the values are return using Employee.java as for get and set method of name and id..
EmployeeSearchService.java
public List searchByName(String name)
// List returnList=new ArrayList();
List results=new ArrayList();
EmployeeDB em=new EmployeeDB();
results=em.searchName(name);
ListIterator langIt=results.listIterator();
while(langIt.hasNext())
Employee emp=(Employee) langIt.next();
String name2 = emp.getName();
String SSNo=emp.getSsNum();
System.out.println("Emp Name:"+ name2);
results.add(name2);
results.add(SSNo);
4. EmployeeDB.java contain the following code..
public class EmployeeDB extends AbstractDAO
public List searchName(String name1)
{      //External Interface
List resultList = new ArrayList();
ResultSet resultSet = null;
Statement aStmt2 = null;
String url="jdbc:odbc:test";
String uname="root";
String pwd="root";
String name="";
try {
Connection con=getConnection();
aStmt2 = con.createStatement();
String query2 = "SELECT SSNO,NAME FROM EMPLOYEE WHERE NAME ='"+ name1 +"'";
cat.debug(query2);
resultSet = aStmt2.executeQuery(query2);
while(resultSet.next()){
Employee tvo = new Employee();
name = resultSet.getString("NAME");
String SsNum1 = resultSet.getString("SSNO");
tvo.setName(name);
tvo.setSsNum(SsNum1);
resultList.add(tvo);
catch (Exception e) {
System.out.println( e);
e.printStackTrace();
return resultList;
My Problem is all the classes are compiled and excute and validation work fine but while the name of employee entered that if name is available in DB table which reply the following error message as,
javax.servlet.ServletException
     org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:516)
     org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:423)
     org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:226)
     org.apache.struts.action.ActionServlet.process(ActionServlet.java:1164)
     org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:415)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
     org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:362)
root cause
java.util.ConcurrentModificationException
     java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
     java.util.AbstractList$Itr.next(AbstractList.java:420)
     com.dao.vertex.EmployeeSearchService.searchByName(EmployeeSearchService.java:77)
     com.dao.vertex.SearchAction.execute(SearchAction.java:36)
     org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:421)
     org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:226)
     org.apache.struts.action.ActionServlet.process(ActionServlet.java:1164)
     org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:415)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
     javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
     org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:362)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.9 logs
Plz reply how to solve send correct code to send data to values of iterate bean.... which line of code i need to modify...
Thanks.

Answer 1

So here is what you are doing:
ArrayList results = //get employees from database
ListIterator langIt = results.listIterator();
while (langIt.hasNext()) {
  Employee emp = langIt.next();
  String name2 = emp.getName();
  String SSNo = emp.getSSNum();
  results.add(name2);
  results.add(SSNo);
}So you get a list or Employee objects, then you get an iterator over the list. For each Employee in the list you add the name and SSNo as Strings back to the same list. From the API for ConcurrentModificationException the exception can be thrown when you modify a collection while iterating over the collection - which is precisely what you are doing.
The ListIterator interface allows you to modify the list through its own methods. Try using:
  langIt.add(name2);
  langIt.add(SSNo);instead.
Why are you taking the name and SSNo out of the Employee object and placing them back in the same List anyway? That makes no sense to me.