Question

Having a Java web application, how does one read properties file only once when the app is deployed (storing them later in some singleton)? Meaning, configuration changes would require redeployment.

Otherwise, is there an alternative way to prevent an app from constantly reading .properties file? Previously I had settings in my web.xml file, but now .properties is required.

Code used to read app settings from JBoss configuration path:

File f = new File(System.getProperty("jboss.server.config.dir"), 
                  "myappsettings.properties");
Properties p = new Properties();
p.load(new FileInputStream(f));
try {
   db_name = p.getProperty("DATABASE_NAME"));
   file_path = p.getProperty("FILE_PATH"));
   ...
} catch (Exception e) {
   ...
}

Answer 1

Implement your own ServletContextListener:

public class PropertiesReadingListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent event) {
        //read properties here...
        event.
          getServletContext().
          setAttribute("db_name", p.getProperty("DATABASE_NAME"));
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
    }
}

You must reference this class in web.xml:

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