need some help in MVC

[mallikarjun dontamsetti]

I just joined in a small company they are using some java code in jsp but i don't like to use java code in jsp. So, i ask permission to my M.D to develop an application M.V.C architecture Using only Servlets,java beans and JSP (No frame work) i am facing some problems like each time opening connection in servlet to connect the database and "setting primary key available to entire/part of some pages" in my application.
Please help me to develop the application and suggest some books and sites need to develop M.V.C pattern
Thanks

[dileep keely]

Can you let us know what is the problem?

[Bosun Bello]

There are several books and articles on he MVC pattern on the internet. I am not exactly clear on your question though, but it sounds like you are opening a connection to the database on each request, and you are concerned right?

[mallikarjun dontamsetti]

My problem is opening Connection in every Sevlet for each table and when i them close at end of servlet, in some jsp it's throwing some exception like statement is closed

[Bear Bibeault]

Why do you need a connection in the JSP? The JSP shouldn't be doing any database access at all. If it is, your code is not following best practices.

[mallikarjun dontamsetti]

I am not opening connection in jsp. I am opening connection in servlet and when i close the connection it is throwing exception like statement is closed

[Bear Bibeault]

I didn't say anything about opening a connection in the JSP. You said:

, in some jsp it's throwing some exception like statement is closed

Why would your JSPs care about a connection? Database access should be over and done with before any JSP is forwarded to. Do you have Java code in your JSPs accessing a result set?

In fact, if you are doing any database access even at the servlet level, you are violating the precepts of MVC. All database access and information should be handled by the Model -- not the Controller or the View.

[mallikarjun dontamsetti]

model means i am using a java class like

//connecting to database

public class LoginDAO {
		private String query="Select * from employee where uname=? and pass=?";
		private PreparedStatement pst;
		
	
		public boolean validate(String uname,String pass){
		
		try{
			
			Connection conn=Connet_Database.getConnection();
			PreparedStatement pstmt=conn.prepareStatement(query);
			pstmt.setString(1, uname);
			pstmt.setString(2, pass);
			rs=pst.executeQuery();
			return rs.next(); 
		}catch(Exception e){
			e.printStackTrace();
		}
		return false;
		
	}

//connecting servlet

public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		
		String uname=request.getParameter("login");
		String pass=request.getParameter("password");
		LoginDAO ld=new LoginDAO();
		
		if(ld.validate(uname, pass)){
			//Start Session
			
			HttpSession session=request.getSession();
			session.setAttribute("userName",uname);
			RequestDispatcher rd=request.getRequestDispatcher("Display");
			rd.forward(request, response);
		}
		else{
			RequestDispatcher rd=request.getRequestDispatcher("Login.html");
			rd.forward(request, response);
		}
		

But it is always going to else statement even i enter the correct values in html page. wat is wrong

[Bear Bibeault]

Does your DAO compile like that? How can you return a result set as a boolean? Where do you close the connection? Why aren't you using a connection pool?

[mallikarjun dontamsetti]

Then how to return result-set? I don't have any idea about connection pooling

[Bear Bibeault]

mallikarjun don wrote:Then how to return result-set?

You never want to return a result set. Results sets should be closed and the statements and connections reclaimed as soon as possible. What data do you need from your DAO? It looks like all you want is a boolean indicating if the record exists or not, but that's not what your code is doing (and your SQL is highly inefficient for that).

I don't have any idea about connection pooling

Time to learn: connection pooling.

[mallikarjun dontamsetti]

and your SQL is highly inefficient for that.

What is this means i can not understand please tell me

[Bear Bibeault]

At this point this has become much more about JDBC than Servlets, so this topic has been moved to the JDBC forum.

[Bear Bibeault]

mallikarjun don wrote:

and your SQL is highly inefficient for that.

What is this means i can not understand please tell me

If you only care whether the record exists or not, why fetch all the data with a "select *"? To check for existence a "select count(*)" will be more efficient.

[mallikarjun dontamsetti]

rs.next() What it returns if value is correct?

[Bear Bibeault]

Easy enough to check... give it a try.

[Jeanne Boyarsky]

mallikarjun don wrote:rs.next() What it returns if value is correct?

When you use count(*), there is no such thing as correct/not correct. rs.next() will always return true and then rs.getInt(1) gives you the number of records the count found. Possibly zero.

[Rudy Gireyev]

Bear Bibeault wrote:
If you only care whether the record exists or not, why fetch all the data with a "select *"? To check for existence a "select count(*)" will be more efficient.

Hi Bear. I'm wondering if select count(*) would really be more efficient than say select username. I'm thinking that for select count(*) it has to read every row in the table no matter what, whereas for select username it will stop searching when the row is found.