Load a file one time for all users

Vaadin 6 / 7 / 8
1

Hi,

I am building an application which, among other things, loads a XML file which is the same for all the users.
If i load this file from the init() method, then if 1000 users open a session, the file will be loaded 1000 times, isn’t it ?
How to load the file one time rather than 1000 times ???

Eric

2

For instance using a ServletContextListener: take a look
at this example
. You can then store the file in a static variable, but remember to handle concurrent access.

3

I used it this way, but the contextInitialized() method is NEVER executed, the init() method is still the first method to be launched :

[size=2]
public class JabberSettingLauncher extends Application implements HttpServletRequestListener, [color=#1d11d2]
ServletContextListener
[/color]{
          public void [color=#1d11d2]
contextInitialized
[/color](ServletContextEvent contextEvent) {...}
          public void init() {...}
[/size]

Is there a method dedicated to the Vaadin context ?

Eric

4

Did you add the listener to your web.xml?

5

1 / You are right Thomas, it works much better !

BUT, when i try to get the attribute from the context inside the init() method,
i get a Null Pointer
 in this example :
Do you know what to do ?

2 / Another question : from my point of view, a listener is supposed to listen to events like clicking on a button, i do nnot understand why we use a listener for a context ??:mellow:

[size=2]

package com.example.test2vaadin;

public class Test2vaadinApplication extends Application [b]
implements ServletContextListener
[/b]{

	ServletContext context;
	
    @Override
    public void init() {
    	Window main = new Window("Hello window");   //window means browser or tab
        setMainWindow(main);
        main.addComponent(new Label("Value of TEST attribute coming from the context : "
                                                +[color=#da1616]
context.getAttribute("TEST")
[/color]));  [color=#bb1839]
=> Null Pointer Exception
[/color]
    }

 	public void [b]
contextInitialized
[/b](ServletContextEvent contextEvent) {
		System.out.println("-------------------    Context Created    ------------------");
		context = contextEvent.getServletContext();
		// set variable to servlet context
		[color=#1baf16]
context.setAttribute("TEST", "TEST_VALUE");
[/color]
	}
	
	public void contextDestroyed(ServletContextEvent contextEvent) {
		context = contextEvent.getServletContext();
		System.out.println("-------------------    Context Destroyed    ------------------");
	}
}

[/size]

Web.xml :

...
[size=2]
<listener>
  		<listener-class>
  			com.example.test2vaadin.Test2vaadinApplication
  		</listener-class>
  	</listener>
</web-app>
[/size]
6
  1. Try getting the Context through the application instead of storing it:
((WebApplicationContext)getContext()).getHttpSession().getServletContext();
  1. Well, this particular one listens to when servlets are started and stopped. Same concept, different scale. The ServletContextListener is part of the Java Servlet standard, not just a Vaadin thing.
7

1 / Your solution works fine, in my case, i get the attribute this way :

[size=2]
main.addComponent(new Label("Value of TEST attribute coming from the context : "
+((WebApplicationContext)getContext()).getHttpSession().getServletContext().getAttribute("TEST")));
[/size]

2 / Ok, i understand.

Thank you Thomas :grin: