Creating Objects in Application Scope at Deploy Time

[raphead]

Hi,

I'm realatively new to JSP and just want to ask wether the following is possible because I think the possibilities of the underlying technology can offer such things.

I would like to create an Object in Application scope that exists for the whole cycle of the container beginning from deployment of my WAR file AND which is instantiated exactly once.
My Question is now: Is that possible with Tomcat/Jboss?

Maybe I explain how I could imagine this functionality to look like:

One writes a class which goes to WEB-INF/classes. in the deployment descriptor one points out that this class has to be loaded with parameters XY. Then one just
does something like application.getAttribute(...) to get a reference to that object and uses it.

I need this for example for my I18N classes that i've wrote, which i don't want to be initalized for each user which loges in seperately.


Many Thanks, T.

[jcordes]

It can be done by writing a javax.servlet.ServletContextListener. This listener is notified upon creation of the context (and when it's destroyed). You have to pass the parameters as context-params, though (the listener-element in web.xml has no param-children). All together:

web.xml

<context-param>
<param-name>i18nResources</param-name>
<param-value>/WEB-INF/application.properties</param-value>
</context-param>

<listener-class>MyListener</listener-class>


listener:

public class MyListener implements ServletContextListener {
public void contextDestroyed(ServletContextEvent e) {
}

public void contextInitialized(ServletContextEvent e) {
ServletContext ctx = e.getServletContext()

String pathToProperties = ctx.getInitParameter("i18nResources");
...
ctx.setAttribute("i18nResources", resources);
}
}

Then you gain access to your resources by calling request.getSession().getServletContext().getAttribute("i18nResources"); (or even easier with ${i18nResources} if your using jstl with el-tags ;-)).

HTH,

Jochen.

[raphead]

Hi, thanks for that hint! Seems really smooth with regard to integration. I think when I'm starting with Servlets, I'll do this.

For now, as I want to stick with JSPs at first and I found a solution: I used a singleton which gets not stored in a static field but in the application scope:


public class ApplicationGlobalData
{
public String applicationUri = "";
public String applicationPath = "";

private ApplicationGlobalData()
{
}

private ApplicationGlobalData(HttpServletRequest request)
{
init(request);
}

private synchronized void init(HttpServletRequest request)
{
if (request.getServerPort() == 433)
{
applicationPath += "https://"+request.getServerName();
} else {
applicationPath += "http://"+request.getServerName();
if (request.getServerPort() != 80)
{
applicationPath += ":"+request.getServerPort();
}
}
applicationPath += request.getContextPath()+"/";
applicationUri += applicationPath+"index.jsp";
}

public static ApplicationGlobalData getInstance(HttpServletRequest request, ServletContext application)
{
ApplicationGlobalData applicationGlobalData;
if(application.getAttribute("ApplicationGlobalData") == null)
{
applicationGlobalData = new ApplicationGlobalData(request);
application.setAttribute("ApplicationGlobalData", applicationGlobalData);
System.out.println("---------------> INIT ApplicationGlobalData");
} else {
applicationGlobalData = (ApplicationGlobalData)application.getAttribute("ApplicationGlobalData");
}
return applicationGlobalData;
}
}


Disadvantage: For each request the Constructor has to check whether already an Object exists.