class variable set to null outside of a servlet - servlets

Question

I wrote a simple servlet, in the doPost I got the user name and the password from a jspand authenticated the user by sending the password entered by the user to the data base(mysql). I got the data correctly and I am redirecting the user to another jsp page called welcome.jsp.
my question is , I wrote this method public String getUser(){return userNmae;}; I put it outside of the dopost method, however it is returning null. I have declared the variable userNmae as a class variable and when I debug , the variable contains a value in the dopost method , but it is null outside of the dopost method.why it is null outside of the dopost method?
I am calling getUser() method in the welcome.jsp page.
here is my code
public class UIclass extends HttpServlet {
public UIclass() { };
private String passWord = null;
private String userNmae = null;
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String name = request.getParameter("userName");
String password = request.getParameter("password");
Connection connection = null;
try {
connection = Connections.getConnection();
java.sql.PreparedStatement statement = connection.prepareStatement("SELECT PASSWORD,USERNAME FROM LOGIN where username =?");
statement.setString(1, name);
ResultSet resultset = statement.executeQuery();
while (resultset.next()) {
passWord = resultset.getString("PASSWORD");
userNmae = resultset.getString("USERNAME");
}
} catch (Exception e) {
// TODO: handle exception
} finally {
if (connection != null)
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
};
}
if (passWord.equalsIgnoreCase(password)) {
RequestDispatcher rd = request.getRequestDispatcher("welcome.jsp");
rd.forward(request, response);
}
}
public String getUser() {
return userNmae;
}
}

Answer 1

I'll answer by giving you a simpler example of what your code is actually doing:
Bottle bottle1 = new Bottle();
bottle1.setMessage("Hi there");
Bottle bottle2 = new Bottle();
System.out.println(bottle2.getMessage());
What would you expect this program to display? I would expect null, because you set a message on bottle1, and read the message from bottle2. These are two different bottles. When you put a message in a bottle, the message is in that bottle, not in the other bottles.
Your code does the same thing.
The servlet container creates an instance (unique) of UIclass. This is equivalent to creating the first bottle in my example.
The servlet is invoked when you send an HTTP request. It sets the user attribute in the servlet. This is equivalent to bottle1.setMessage("Hi there") in my example.
The container executes your JSP, which contains the code
<jsp:useBean id="uiclass" class="com.servlet.UIclass" scope="request">
This creates a new UIClass instance. It is equivalent to creating the second bottle in my example.
The JSP calls uiclass.getUser(). This is equivalent to getting the message from the second bottle in my example.
There are many, many things wrong in your code:
You shouldn't use scriptlets, and jsp:useBean tags
You should never create instances of servlets by yourself. A servlet is meant to be instanciated and called by the container.
You should realize that a unique servlet instance is called to serve, concurrently, all the requests of all the users to this servlet URL. Storing user-specific data in servlet attributes is thus really wrong
You probably want the user name to be available for all the subsequent requests of this user. That's what the HTTP session is for. You should store the user as an attribute of the HTTP session: request.getSession().setAttribute("userName", userName)
The JSP should use the JSP EL and the JSTL to access beans stored in the request or the session by the servlet:
<c:out value="${userName}"/>