Solved

how do client get data packet returned from EJB method (public List getResultset(String sql)) ?

Posted on 2003-11-23
6
488 Views
Last Modified: 2013-11-24
Hi,
  where I define one method in Entity bean which return query result,I test it in Entity bean body,it can get right return.But from client ,I can not get returned data. What is the reason for that?
java.lang.NullPointerException

      void com.evermind.server.rmi.RMIConnection.EXCEPTION_ORIGINATES_FROM_THE_REMOTE_SERVER(java.lang.Throwable)

            RMIConnection.java:1558

      java.lang.Object com.evermind.server.rmi.RMIConnection.invokeMethod(com.evermind.server.rmi.RMIContext, long, long, java.lang.reflect.Method, java.lang.Object[])

            RMIConnection.java:1511

      java.lang.Object com.evermind.server.rmi.RemoteInvocationHandler.invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[])

            RemoteInvocationHandler.java:55

      java.lang.Object com.evermind.server.rmi.RecoverableRemoteInvocationHandler.invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[])

            RecoverableRemoteInvocationHandler.java:22

      java.util.List __Proxy1.getResultset(java.lang.String)

      void Samplebbs_live.Tb_userClient.main(java.lang.String[])

            Tb_userClient.java:84

  Entity Bean:
  public List getResultset(String sql)
  {
   List list = new ArrayList();      
    try
   {
    dbconn = getConnection();
    st = dbconn.createStatement();
    rs = st.executeQuery(sql);
    ResultSetMetaData mtdata = rs.getMetaData();
    if (rs==null)
    {
      System.out.println("null data");
      return Collections.EMPTY_LIST;      
    }      
    int col = mtdata.getColumnCount();
    while (rs.next())
    {
       map = new HashMap(col);
       for (int i=1;i<=col;i++)
       {
           map.put(mtdata.getColumnName(i),rs.getString(i));                
       }
       list.add(map);
    }
    dbclose(st,rs,dbconn);
    for (int j=0;j<list.size();j++)
   {
     Map m = new HashMap(col);
     m = (Map)list.get(j);
     System.out.println(j);
     System.out.println((String)m.get("mailaddr"));
   }
   }

   catch (Exception se)
   {
     se.printStackTrace();
     return Collections.EMPTY_LIST;
   }   System.out.println("4");
    return list;
  }
but when I called it from client by the following way:
...............
      List lt = new ArrayList();
      lt = tb_user.getResultset("select * from tb_user");    ---error here
     //tb_user ---EJB Object
..............
0
Comment
Question by:hexiaoquan
  • 3
6 Comments
 
LVL 35

Expert Comment

by:girionis
ID: 9809290
 Can you do a System.out.println(list) in your EJB before this line: return list; and tell us the output?
0
 
LVL 35

Expert Comment

by:girionis
ID: 9809297
 Also look at the server console/logs for any possible exceptions.
0
 

Author Comment

by:hexiaoquan
ID: 9809357
Yeah,I can get System.out.println(List) in EJB

  for (int j=0;j<list.size();j++)
   {
     Map m = new HashMap(col);
     m = (Map)list.get(j);
     System.out.println(j);
     System.out.println((String)m.get("mailaddr"));
   }

 It can run well.
Now I get the right answer,Return value Type shout implements java.io.Serializable,
but list do not implement it.so I change it to Vector or rowset.It is ok now

thanks.
0
 
LVL 35

Expert Comment

by:girionis
ID: 9809361
 Ah... yes true, the object should implement serializable if you want to return it...

  Please ask a question here http://www.experts-exchange.com/Community_Support/ for zero points to PAQ the question and refund the points to you.
0
 
LVL 1

Accepted Solution

by:
DarthMod earned 0 total points
ID: 11688317
Submitted to PAQ with points refunded (50)

DarthMod
Community Support Moderator
0

Featured Post

Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
International Data Corporation (IDC) prognosticates that before the current the year gets over disbursing on IT framework products to be sent in cloud environs will be $37.1B.
Viewers learn how to read error messages and identify possible mistakes that could cause hours of frustration. Coding is as much about debugging your code as it is about writing it. Define Error Message: Line Numbers: Type of Error: Break Down…
Viewers will learn about the different types of variables in Java and how to declare them. Decide the type of variable desired: Put the keyword corresponding to the type of variable in front of the variable name: Use the equal sign to assign a v…

856 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question