why is the List returning empty?

[Vic Hood]

Hi folks ,
Im developing a web app where im trying to pass the value of a list from the database through a DAO class onto a servlet which displays it in a jsp when called , however im not being able to call the function which generates the List in the servlet as a result a null List is returned .any ideas why this is happening ?
My servlet class generating the list.

		if((actcode!=null)&& (actcode.trim().equals("GETDOMLIST"))){
								System.out.println("test block domlist");
								domList=DataObject.getDomList();
								request.setAttribute("domList", domList);
								RequestDispatcher rd = request.getRequestDispatcher("POC.jsp");
								rd.forward(request, response);
								bean.setDomainTypeOid(domainType_Oid);
							}

Thanks in advance

[amit punekar]

Hi,
Did you try printing the contents of the "domList" in the servlet?

[Vic Hood]

I did by doing this

	domList=DataObject.getDomList();
								for(int i=0;i<domList.size();i++){
									System.out.println("DomList is"+domList.get(i));
								}
								request.setAttribute("domList", domList);
								RequestDispatcher rd = request.getRequestDispatcher("POC.jsp");
								rd.forward(request, response);
								bean.setDomainTypeOid(domainType_Oid);

However it threw a NPE while accessing domList..

[amit punekar]

Hi,
That does mean your DataObject needs to be debugged as it sends you the List.

Regards,
Amit

[Vic Hood]

well my DataObject is the DAo object and the associated function for getting the records is as below

	public void setDomList(ArrayList domList) {
			this.domList = domList;
		}
		public List getDomList()throws Exception {

		if(domainType_Oid!=0 && domainType_Oid!=-1){
		int dt_oid=domainType_Oid;
		Connection con = null;
		PreparedStatement stmt = null;
		ResultSet rs = null;
		DomainBean domainBean=null;
		System.out.println("The domaintype being accessed by listDomain has dt-oid="+dt_oid);
		System.out.println("Listing records in DAO");
		domList =new ArrayList<DomainBean>();
		try {
			con= DBConnector.getConnection();
			if (con != null){
				System.out.println("Connected");
			String query= "SELECT OBJECTID,CODE,DESCRIPTION,ISEDITABLE, ISACTIVE FROM DOMAIN WHERE DOMAINTYPE_OID='"+dt_oid+"' ORDER BY DOMAINTYPE_OID,OBJECTID " ;
			System.out.println(query);
			stmt = con.prepareStatement(query);
			
			rs = stmt.executeQuery();
			while (rs.next()){
				System.out.println("In While");
				domainBean= new DomainBean();
				domainBean.setObjid(rs.getInt("OBJECTID"));
				System.out.println("The value of Objid"+domainBean.getObjid());
				domainBean.setCode(rs.getString("CODE"));
				if (rs.getString("ISACTIVE").equals("1"))
					domainBean.setstatusActive("Yes");
				if (rs.getString("ISACTIVE").equals("0"))
					domainBean.setstatusActive("No");
				if (rs.getString("ISEDITABLE").equals("1"))
					domainBean.setstatusEdit("Yes");
				if (rs.getString("ISEDITABLE").equals("0"))
					domainBean.setstatusEdit("No");
				domainBean.setDescription(rs.getString("DESCRIPTION"));
				System.out.println("The value of Code"+domainBean.getCode());
				System.out.println("The value of Description"+domainBean.getDescription());
				System.out.println("The value of Status Active"+domainBean.getstatusActive());
				domList.add(domainBean);
				System.out.println("The size of domList is"+domList.size());
			}
//				System.out.println("Objectid in DAO-ListDomain  "+domainBean.getObjid());
					}
			}catch (SQLException sqe) {
				sqe.printStackTrace();

			} finally {
				DBConnector.closeResultSet(rs);
				DBConnector.closeStatement(stmt);
				DBConnector.closeConnection(con);
			}
			
			
		}

			
		return domList;
		
		}

Am I missing something here?

[James Sabre]

It's not obvious to me why you need the method setDomList() since you always create a new list in the getDomList(). Also, why does domList need to be an instance variable?

[amit punekar]

Hello,
What does this print ?

System.out.println("The size of domList is"+domList.size());

[Vic Hood]

James Sabre wrote:It's not obvious to me why you need the method setDomList() since you always create a new list in the getDomList(). Also, why does domList need to be an instance variable?

Well I was using domList as a bean instance variable and hence the getter and setters.I wanted to access it in my jsp through a bean.
And for amit's q.. thats not being printed , I guess the control never reaches that statement

[amit punekar]

Yeah.
You debug that thing and you should be fine after fix.

Regards,
Amit

[Vic Hood]

amit punekar wrote:Yeah.
You debug that thing and you should be fine after fix.

Regards,
Amit

Im trying to figure out how to debug here , any help would be appreciated. THE DAO object"DataObject ' is created and called , thats pretty starightforward. Ive inserted logging pretty much everywhere i could be going wrong, checked the DB however the List is still empty

[amit punekar]

Hello,
I can think of two things here -
1) Check if the query that is printed from your program if it returns you any results.
2) If yes then then check your DB connection details to confirm if you are connecting to the same database on which you ran the query #1.

Regards,
Amit

[Mike Zal]

I also have a question about your the following Servlet code

domList=DataObject.getDomList();
...
RequestDispatcher rd = request.getRequestDispatcher("POC.jsp");  
rd.forward(request, response);  
bean.setDomainTypeOid(domainType_Oid);  

Did you mean to do the following?

DataObject.setDomainTypeOid(domainType_Oid);
domList=DataObject.getDomList();

It seemed weird that you were trying to set the domainType of a variable that is not show where it is declared or what it does. It is also strange that you change its value after you send the request dispatch forward.

[Vic Hood]

Mike Zal wrote:

DataObject.setDomainTypeOid(domainType_Oid);
domList=DataObject.getDomList();

It seemed weird that you were trying to set the domainType of a variable that is not show where it is declared or what it does. It is also strange that you change its value after you send the request dispatch forward.

Well Mike,
I wouldnt be able to directly implement your code snippet as I cannot access the setDomainType_Oid through DataObject as SetDomainType_Oid is setter method of the instance variable bean , so i would need to do something like
DataObject.bean.setDomainType_Oid(domainType_Oid);
which is syntatically wrong . Any ideas on how I could go about doing it?

[amit punekar]

Hi,
All Mike is trying to point out possible error in the way you are calling the function setXXX() and not syntactically.
You seems to be using "domainType_Oid" as part of string concatenation in your SQL. If this is true then shouldn't you be setting this value before you invoke "getDomList()" which uses this value as mentioned above.

Regards,
Amit

[Mike Zal]

Have you verified any of the following:
domainType_Oid is not equals to 0 or negative one
Are you successfully connecting to the database
Did the query return any value?

I think your problem is that you are not setting the domainType_Oid variable (it explains why you are receiving a NullPointerException). Can you add some debug to print the value of domainType_Oid to the system log before the first if statement?

[Vic Hood]

hi Mike and Amit,
Thank you for your replies. Iwill try to explain where i could be going wrong here..

amit punekar wrote:Hi,
All Mike is trying to point out possible error in the way you are calling the function setXXX() and not syntactically.
You seems to be using "domainType_Oid" as part of string concatenation in your SQL. If this is true then shouldn't you be setting this value before you invoke "getDomList()" which uses this value as mentioned above.

Regards,
Amit

I didnt quite understand this.

Mike Zal wrote:Have you verified any of the following:
domainType_Oid is not equals to 0 or negative one
Are you successfully connecting to the database
Did the query return any value?

I think your problem is that you are not setting the domainType_Oid variable (it explains why you are receiving a NullPointerException). Can you add some debug to print the value of domainType_Oid to the system log before the first if statement?

Well , I did the check for domaintype_oid in my DAO class , however that code is not executed . I do know that im being able to connect to the database .Because I populate a drop down in my jsp through a dynamic list from the database.But As far as getting this list goes it returns only a NULL , im not being able to figure out why , imo its not even reaching the DB code ,ie. DAO class.
Awaiting your replies.

[venkat prathap]

Hey,

Can you share me exception log you are getting...

[Vic Hood]

There was no exception log . Because the list is empty

[Joseph Mokenela]

All the

 System.out.println()

statements that are inside the

while (rs.next()){ }

is there any one of them which is printing?

[Vic Hood]

Nope. They are not being printed either.

[Joseph Mokenela]

The problem could also be that your ResultSet is empty, have you checked that your query returns the results from the database?

[Vic Hood]

Tried the query in the DB , and works perfectly there .returns the expected result set.

[Joseph Mokenela]

what about the very first if statement,

if(domainType_Oid!=0 && domainType_Oid!=-1){}

.
Did you check whether your domainType_Oid satisfies the conditions in the if statement?

[Vic Hood]

Yes im printing the value of domainType_Oid in the servlet and the if condition is satsfied before entering the loop.

[Joseph Mokenela]

Did you check that your connection is not null? does this statement print?

System.out.println("Connected"); 

[Vic Hood]

Yes it does print!But Any idea where im going wrong?

[Mike Zal]

Vic, could you please post exactly which debug statements are being printed and which ones are not being printed. After reading your posts, it seems like you are seeing the following debug

"The domaintype being accessed by listDomain has dt-oid="+dt_oid
"Listing records in DAO"
"Connected"
//The complete sql query

After the echoed query there is no other output. Is this correct?

[Vic Hood]

Hi Mike, the exact debug statements are as follows
the various points where these statements occur are--

loadDomaintype DAO//DAO.java..
Connectionorg.postgresql.jdbc3.Jdbc3Connection@81b1fb//DB connection
loadDomaintype DAO try block//DAO class
Connected//DAO class
inside loadDomainType//DAO class
DomainType code=MARITALSTATUS, objid=1, description=MaritalStatus
ChkList val1
DomainType code=GENDER, objid=2, description=gender
ChkList val2
DomainType code=EMPGROUP, objid=3, description=employeegroup
ChkList val3
DomainType code=UserType, objid=4, description=UserType
ChkList val4
I think domList is being accessed//JSP
log4j:WARN No appenders could be found for logger (org.displaytag.export.ExportViewFactory).
log4j:WARN Please initialize the log4j system properly.
setting Domain To2//Sevlet
the domaintype oid selected is2
The integer value of objid0//DAO
Set Domain ID2//Servlet
DomainType_oid2
test block domlist
 DomainBean.java--domainTypeOid is 2//Bean class

Hope that helps

[Mike Zal]

Not really since none of the debug you printed seems to match what is inside the getDomList() method. Either your System.out.print statements are printing somewhere else or the code is never being executed. Can you try making a small change to your code and see if you see any of the new debug.

if(domainType_Oid!=0 && domainType_Oid!=-1) {
    //normal processing
} else { //added else statement
    System.out.println("Skipped All Processing in DataObject class");
}

//Add debug before the return statement
if (domList == null) {
    System.out.println("Returning null domList");
} else if (domList.size() == 0) {
    System.out.println("Returning empty domList");
} else {
    System.out.println("Returning domList with size: "+domList.size());
}
return domList;

[Vic Hood]

Mike Zal wrote:Not really since none of the debug you printed seems to match what is inside the getDomList() method. Either your System.out.print statements are printing somewhere else or the code is never being executed. Can you try making a small change to your code and see if you see any of the new debug.

if(domainType_Oid!=0 && domainType_Oid!=-1) {
    //normal processing
} else { //added else statement
    System.out.println("Skipped All Processing in DataObject class");
}

//Add debug before the return statement
if (domList == null) {
    System.out.println("Returning null domList");
} else if (domList.size() == 0) {
    System.out.println("Returning empty domList");
} else {
    System.out.println("Returning domList with size: "+domList.size());
}
return domList;

Yep you'd guessed right.The domList is set to null
Heres the debug code..Please help on how I could get it to work

...
Set Domain ID1
DomainType_oid1
test block domlist
 DomainBean.java--domainTypeOid is 1
Skipped All Processing in DataObject class//
Returning null domList//
....

[Mike Zal]

Since "Skipped All Processing in DataObject class" appeared in your debug, it means that domainType_Oid equals 0 or -1. You need to set that variable after you instantiate the DataObject but before you call getDomList().

[Vic Hood]

Hi Mike,
You were right . The value of Domaintypeoid is being set to zero(checked by logging) . The thing is im being able to retrieve the required value of domaintypeoid in my servlet , how do I pass the same value to my DAO class , so that i can set the value of domaintype-oid before the if loop is executed?

[Mike Zal]

In the Servlet, you could set the DAO object as a request attribute. In your JSP, you could just use the request.getAttribute instead of instantiating a new DAO object.

[rav pad]

Vic,
Can you suppply the log of the whole thing starting from the first if
if(domainType_Oid!=0 && domainType_Oid!=-1){} because I see that the log which you have already supplied does not match with the System.Out.Println given in the code.

Also place the execute query in a System.out.println so that we will know whether a resultset is getting generated or not.

[Vic Hood]

Hi Folks,
Solved this for now .
The thing is i was creating a local variable to generate the List , however was not instantiating it with the value returned from the DAO class.