addon for "Technical Problem" posted by Kuching

Hi poweranger77,

You should not mixup servlet/front-end/display logic with business logic.
So, never put target_url or source_url in C. Better way to do this is to
throw a exception in C whenever an error occurs. In your servlet, once you
catch that exception, you know something is wrong and can do a workaround
for it.

________
radarsh

radarsh, yeah, i am totally agree. And i think dont understand my Q.

What i am trying to seek is the proper way of handling this kind of messageObject. Where should i put it is the most ideal way. If i dump this in the Manager (C), i will not able to know how to set the ratget_url and source_url. And if i dump it in the Servelt, i would not able to catch the error as most of the tiime the error happend during the transaction process.

share with me, how you all implement this kind of messageObject

It depends on whether it's part of the model or not. If you caonsider the MVC pattern which is implemented in Struts, this is how it would work, as in this pseudocode

doGet(response, request){
      HttpSession session = request.getSession() ;
      try{
            Manager managerObject = new Manager(//args) ;//create DB Manager object, provide with args/parameters
            MessageObject mo = managerObject.getMessageObject() ;
            if( MessageObject.validate() ){ //validate method to check it's all okay
                  //MessageObject has no business exceptions
                  session.setAttribute("mo" , mo);
                  RequestDispatcher rd = request.getRequestDispatcher("success.jsp") ;
                        rd.forward(request, response) ;
            }else{
                  //MessageObject has business exceptions
                  //this could be duplicate info or well formed but erroneous data
                  session.setAttribute("mo" , mo);
                  RequestDispatcher rd = request.getRequestDispatcher("failure.jsp") ;
                        rd.forward(request, response) ;
            }
      }catch(SQLException se){
            //there has been an application level error/exception, i.e. can't get connection to db
            request.setAttribute("appError" , se) ; //so the error page has access to the exception
            session.setAttribute("mo" , mo); //still keep the data
            RequestDispatcher rd = request.getRequestDispatcher("error.jsp") ;
            rd.forward(request, response) ;
      }
}

Hi,

bloodredsun way of handling is good.

One more thing i don't understand is to keep the target_url and source_url in messageObject. What purpose does it solve?

If the target_url is dependent upon the exceptions thrown in the MessageObject, then it can very well be handled in the servlet with the request dispatcher to an appropriate error page.

regards,
fargo





 

bloodredsun, i assuem this line [ Manager managerObject = new Manager ] will start the db/business logic transaction.

Thus, i am wondering, for this line [  if( MessageObject.validate() ){ //validate method to check it's all okay ]  the system definitely will able to return true or NoError message since it's not connected to the ManageObject at all.

For this block,
[
catch(SQLException se){
          //there has been an application level error/exception, i.e. can't get connection to db
          request.setAttribute("appError" , se) ; //so the error page has access to the exception
          session.setAttribute("mo" , mo); //still keep the data
          RequestDispatcher rd = request.getRequestDispatcher("error.jsp") ;
          rd.forward(request, response) ;
     }
]
I am in serious doubt that the it can catch any error happending in the DB/logic trasncation object, which is in this place is [ managerObject ]. Becasue all the possible transaction is happending there and in the servlet, i am not able to cathc those errors.

Thats why i plan to set the MessageObject in the DB/Logic object. But then, another problem. how can i ser the targetUrl and SourceUrl there? After all, it'll automatically route to that JSp as instructed.

Fargo, targetURL and sourceURl is for the system to redirect to the correct page after the messageObject dont his job. If there is an error, it'll back to the source_url. If it's success, it'll go to the targetURL.

fargo, here you go... entire flow...

jsp:
==
..
<form action="servletA" method="POST" >
..
..
<input type="submit" Value="Add Item">
..

servletA:
=====
doGet() {

  String user_name = request.getParameter("user_name");
  String password = request.getParameter("password");
  String role = request.getParameter("role");

  UserManager um = new UserManager();
  um.insertData(user_manager, password, role);
  RequestDispatcher dispatcher = req.getRequestDispatcher("targetUrl.jsp");
  dispatcher.forward(req, res);

}

UserManager.java
============
..
..
 public void inserData(String user_name, String password, String role) {
    try {
      Class.forName("com.mysql.jdbc.Driver").newInstance();
      String url="jdbc:mysql://localhost:3306/netradb?user=root&password=password";
      conn = DriverManager.getConnection(url);
      Statement stmt = conn.createStatement();
      String sql = "INSERT INTO TABLE_A (user_name, password, role)......";

      int result = stmt.executeQuery(sql);
       System.out.println("Number of row affected " + result);
     
   } catch (Exception e)  { e.printStackTrace(); }
   } finally (Exception e)
     {  if (conn!=null) conn.close();
        if (stmt!=null) stmt.close();
     }
}

*************
In a certain way, i do agree with both of you, that servlet should handling the traffic, which means controlling the targetUrl and sourceUrl. So, if i would do that, i will need to only check the messageObject in the manager level. But then few question on this:

1. How can i redirect the message from MessageObject to the jsp? By using session?
2. Can  the messageObject able to capture the error happend in the Manager's transaction above? i means the DB/SQL transaction..
3. Do i need to declare the entire MessageObject's method, variable as a static ?
 

what i dont understand is, when there is an error happend in the manager level, the entire system will be down and stop. So, how can i still able to passback the error Message to servlet and to jsp for user.

guys, i have an ideas..

what happend if i calling the MessageObject in the servlet level, and in the ManagerLevel, i catch my own exception, call MyException and throw it to the servlet.

And i the servlet i will catch that MyException. If there is no MyException catch, i shall declare as a succesful transaction if not that MyException is the error one.. and redirect from there..

but how can i declare my own exception? and is it workable?

thanks guy, i thikn i have finally come out with the conclusion.

i will declare it in the servlet level.

then i will throws the error that potentially will happend in the managerlevel. in the servlet level i will try to catch it if any.

then from there i shall decide if there is an error, i will redirect it to the error.jsp in the catch block. if none, then i will consider to forward this message to redirect to the correct page.