Database Access Repeated Each Time

Hello dear members,
I want to display some sub categories when i click on a category. I sent the category ID using query string from jsp to servlet. in that servlet i wrote JDBC codes, executed query and saved all the subcategories in a List. Later I dispatched that to a JSP to show them. my servlet code is following:

public class MyGenericServlet extends HttpServlet implements javax.servlet.Servlet {
   static final long serialVersionUID = 1L;
   
   Connection con = null;
   Statement stmt = null;

String jdbcDriver = "com.mysql.jdbc.Driver";

String url = "jdbc:mysql://localhost:3306/craigslistdb";
   String userName = "root";
   String password = "Password";

ResultSet subCategoryRS = null;

List subCategoryList = new ArrayList();
  
   Iterator it = null;

public MyGenericServlet() {
		super();
	}   	
	
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		String catIDs = request.getParameter("catID");
		String catName = request.getParameter("catName");
		System.out.println("catIDxxx"+catIDs);
		
		Double catID = Double.parseDouble(catIDs);
		
		try
		 {
		    Class.forName (jdbcDriver);
		    con = DriverManager.getConnection(url, userName, password);
		    stmt = con.createStatement();
		    subCategoryRS = stmt.executeQuery("SELECT * FROM tblsubcategory where category="+catID);
		    System.out.println ("Database connection established");
		    while(subCategoryRS.next()){
		    	subCategoryList.add(subCategoryRS.getLong(1));
		    	subCategoryList.add(subCategoryRS.getString(2));
		    }
	
		 }
		 catch (Exception e)
		 {
		     System.err.println ("Cannot connect to database server");
		 }
		 finally
		 {
		     if (con != null)
		     {
		         try
		         {
		             con.close ();
		             System.out.println ("Database connection terminated");
		         }
		         catch (Exception e) { /* ignore close errors */ }
		     }
		 }
		
		request.setAttribute("subCategoryList", subCategoryList);
		
		request.setAttribute("catName", catName);
		RequestDispatcher rd = getServletContext().getRequestDispatcher("/pages/AllSubCategoryByCategoryID.jsp");
		rd.forward(request, response);
		
	}

The sub category list is iterated & displayed in the jsp page.

But the problem is- the Sub categories are repeated and appended bellow each time i request.

what I guess is the servlet's jdbc code is accessed every time.

Could you please elaborate on this??

Thanks in advance

Servlets are initialized once, so your method doGet is appending sub-categories to 'subCategoryList' each request.

Initialize subCategoryList to nothing or null, then in doGet you must create a new List each time. Or you could clear the list before adding sub-categories.

Never use request specific objects as instance varibles in Servlet class.
List subCategoryList = new ArrayList();

Move the above statement into doGet method.

Thanks a lot guys! The problem is solved

as you suggested- i moved the List declaration inside the method & it did the job.

Thanks again for being so helpful