Java server pages

Integrating COBRA objects with Java Server Pages is a breeze. COBRA objects already support the Java Beans pattern of getter and setter methods. The following example (JSP 1.0) shows an HTML form and a login bean (that is also a COBRA persistent object).

First we have to specify which bean we want to use:

<%@ page import="uk.co.kimble.jams.Account" %>
<jsp:useBean id="loginBean" class="uk.co.kimble.examples.Account" scope="session"/>

<jsp:setProperty name="loginBean" property="*"/>

The COBRA object is called Account, the JSP engine creates an instance of account called loginBean that exists for the session, alternative scopes are page and application.

<%
// take user straight to admin page if they are logged in

if (loginBean.logged_in) {
pageContext.forward("next.jsp10");
}
%>

If the user is already logged in, then the form is skipped and the user is forwarded to the next page. Otherwise the user is prompted to enter a username and password. To save the user re-typing unnecessary data the username value is extracted from the bean. We may even have saved this value on the user’s browser using a cookie so that it is there at the start of a new session.

<%= loginBean.getReply() %>

The account bean has two variables corresponding to the column names in the account table: username and password. There are setters and getters for these values as well as a getReply() method and a setConnect() method. These methods are ignored by COBRA because they do not correspond to columns in the class_dictionary.

On the first run through the form username is set to blank and the reply text "click enter to log in to server" is displayed at the bottom of the form. When the form is submitted tce data is sent to the server via the URL query string (as specified by the default GET method). Where the form data names correspond to the included bean method names each settor is called in turn.

That is the username is set to the entered username value, the password is set to the entered password value and the setConnect() method is called with the String parameter "Enter".

package uk.co.kimble.examples;

import uk.co.kimble.cobra.rmi.*;
import java.rmi.Naming;

public class Account extends PersistentObject {
    String username = "";
    String password;
    public boolean logged_in = false;
    public String reply;

    public Account() {
        super();
        init();
    }

void init () { reply = "Click enter to login to server"; }

public String getPassword() { return password; }

public void setPassword(String s) { password = s; }

public String getUsername() { return username; }

public void setUsername(String s) { username = s; }

public String getReply() { return reply; }

    public void setConnect(String s) {
        try {
            PersistentObjectFactory rof = (PersistentObjectFactory)
            Naming.lookup("//monte-carlo/JamsServer");

PersistentSource pos = rof.getPersistentSource();
Account a = (Account) pos.retrieve(this);

            if (a.getPassword().equals(password) {
                logged_in = true;
            } else {
                reply = "Incorrect username or password<br>";
            }
        } catch (Exception e) {
            reply = "Could not log in, please check your username and password<br><i>" + e.toString() +"</i><br>";
            logged_in = false;
        }
    }
}

The setConnect() method connects to the COBRA server using RMI (yes this is a 3 or 4 tier application depending on how you look at things). The user account corresponding to the submitted username is retrieved and the passwords compared. If there is a match logged_in is set to true (so when we drop through the form again we are taken to the new page) otherwise the reply message is changed to warn the user of the error. In practise we wouldn’t want to do the RMI lookup every time we action the bean so this would be shifted off somewhere else, probably to another bean with session scope.