Question

I’m using SQLite as my database, and I’m a little bit confused about how I’d configure the path to it. Basically, I have a static String in one of my classes ( which, after initialization turns to something like this ):

private static String DATABASE = "db/my.db";

The folder db is located directly under WebContent, so, to get access to it, I need to use a ServletContext‘s getRealPath method. To use that, I need access to a servlet, and since I’m not sure which servlet will be the first one to be called, I need to perform a check in all of my requests to see if the database has been set, and if it hasn’t then set it. I think there should be a better way of doing this.
For the moment, I created an abstract class which inherits from HttpServlet, adds 2 methods, a getImpl and a postImpl ( both abstract ), and my doGet and doPost are currently implemented like this:

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        App.checkDatabase(this);
        try {
            getImpl(request,response);
        } catch(Exception e) {
            throw new RuntimeException(e);
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        App.checkDatabase(this);
        try {
            postImpl(request,response);
        } catch(Exception e) {
            throw new RuntimeException(e);
        }

And my checkDatabase method is implemented like this:

public static void checkDatabase(HttpServlet servlet)
{
    if(App.DATABASE == null) {
        App.DATABASE = "jdbc:sqlite:"+servlet.getServletContext().getRealPath(
            servlet.getServletContext().getInitParameter("DATABASE")
        );
    }
}

The way I’m doing things right now doesn’t feel right. Surely there must be a better way.

Answer 1

You would like to use a ServletContextListener to hook on webapp’s startup and initialize applicationwide parameters. Here’s a kickoff example assuming that you indeed have definied the path as a <context-param> with <context-name> of DATABASE:

public class Config implements ServletContextListener {

    public void contextInitialized(ServletContextEvent event) {
        String database = event.getServletContext().getInitParameter("DATABASE");
        // ...
    }

    // ...

}

Which you then map in web.xml as follows:

<listener>
    <listener-class>com.example.Config</listener-class>
</listener>

You can if necessary store contextwide variables in ServletContext so that any servlet in turn can access it.

event.getServletContext().setAttribute("database", database);

…

Database database = (Database) getServletContext().getAttribute("database");

As Pascal hinted in his answer, you’d like to use under each JNDI for this. In that case, you can store the JNDI name as <context-param> and obtain/initialize the DataSource (indirectly) in the ServletContextListener that way.

For more hints you may find this basic example useful.