Java - Dynamic Web Project - Global Object

Question

Im interesting in Creating a Global Object which will be shared by all my servlets and all my JSP files. But i dont understand how to do it. Please advice.

for a senario this object would contain lots of information my servlets and jsp files would like to take information from. I know how to pass objects between servlets and jsp's. But i dont know how to initialize 1 global object for the whole "system" or" website"

<display-name>WebTest1</display-name>
<listener>
    <listener-class>listeners.AppListener</listener-class>
</listener>
<welcome-file-list>
    <welcome-file>MainPage.html</welcome-file>
    <welcome-file>MainPage.htm</welcome-file>
    <welcome-file>MainPage.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
    <servlet-name>SimpleServlet</servlet-name>
    <servlet-class>servlets.SimpleServlet</servlet-class>
</servlet>

Luiggi Mendoza · Accepted Answer · 2014-06-13 17:49:15Z

4

You should store the object inside application context. You can do this when the application starts using ServletContextListener.

public AppListener implements ServletContextListener {

    public void contextInitialized(ServletContextEvent sce) {
        //application is being deployed
        //register the "global" object here
        ServletContext sc = sce.getServletContext();
        MyGlobalClass globalObject = ...
        sc.setAttribute("globalObject", globalObject);
    }
    public void contextDestroyed(ServletContextEvent sce) {
        //application is being undeployed
    }
}

Register this class as a listener in web.xml:

<listener>
    <listener-class>package.where.defined.AppListener</listenerclass>
</listener>

Then you can access to this object in both Servlet and JSPs:

Servlet:

public void doGet(...) throws ... {
    ServletContext servletContext = request.getServletContext();
    MyGlobalClass globalObject = (MyGlobalClass)servletContext.getAttribute("globalObject");
    //use it...
}

JSP:

${globalObject.someField}

edited Jun 13, 2014 at 17:49

answered Jun 13, 2014 at 17:44

Luiggi Mendoza

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15 Comments

Eran Over a year ago

in this implementation, say i have 10 servlets. how exactly all those servlets know my global object? And when does AppListener runs? When i start my server it runs?

Luiggi Mendoza Over a year ago

@user1804659 the listener will be fired automatically when the application is deployed and undeployed. The ServletContext is a global object for the whole application. Every servlet may access to ServletContext by using HttpServletRequest, you can access to any object in JSP using Expression Language (that thing inside ${}).

Eran Over a year ago

Now its much CLEARER! Thanks alot mate. I will try this on and see what comes of it!!!

Eran Over a year ago

Luiggi, I want to ask u another question if its ok. If i can access my Object in the JSP file, why would i want to use a servlet? When i can clearly write what ever code i wish in the JSP file ?

Luiggi Mendoza Over a year ago

@user1804659 you asked how can you access to this object in Servlets and JSP, and I showed how you can. If you need to access to this global object in one or in others, will entirely depend on your specific functional requirements.

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