Can servlets in individual contexts have access to the same session object?

[O. Ziggy]

I am trying to write a simple program where i can put a HashMap on an application scoped session and get two applications/contexts deployed as two war files access the HashMap.

Servlet 1

    public void doGet(HttpServletRequest request, HttpServletResponse response)
    	throws IOException{
    		PrintWriter out = response.getWriter();
    
    		HashMap<String ,String> hm = new HashMap<String, String>();
    		hm.put("1", "1");
    		
    		this.getServletContext().setAttribute("usermanager", hm);
    		this.getServletConfig().getServletContext().setAttribute("usermanager2", hm); 	
    	}

Servlet 2

	public void doGet(HttpServletRequest request, HttpServletResponse response)
	throws IOException{
	
		HashMap newMap2 = (HashMap) this.getServletConfig().getServletContext().getAttribute("usermanager"); 
		HashMap newMap3 = (HashMap) this.getServletContext().getAttribute("usermanager2"); 
		
		System.out.println("newmap2 size " + newMap2.size());
		System.out.println("newmap3 size " + newMap3.size());	
	}

To test this i restarted Tomcat 6 then run access Servlet 1 first so that it initializes the Hashmap object. When i subsequently access Servlet 2 i get a NULL-POINTER error which is pointing at the line number where i tried to call newMap2.size()

What am i doing wrong?

    java.lang.NullPointerException
    	at com.TestServlet.doGet(TestServlet.java:24)
    	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
    	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    	at java.lang.Thread.run(Thread.java:619)

[Bear Bibeault]

First of all, you are not storing the object in session scope, you are storing it in application scope.

Secondly, each web context has its own application scope and other web app's cannot simply access it.

[O. Ziggy]

Is there any way i can one of the applications to see the data of the other application?

[Rob Spoor]

I think you should ask yourself if these two web applications actually need to be separate applications in the first place. If they need each other's objects then they are tightly coupled and should perhaps be merged into one application.

[lakshmana dhanimireddi]

I think it's better to save the content in a database like oracle from one servlet and access the content in that database from another servlet.

[Pete Nelson]

While one application context cannot communicate internally with another, there are any number of ways two contexts could share information. A previous poster suggested a database for a persistence layer, which is a pretty common approach. Other options include reading / writing a local file both contexts would have access to, or even using HTTP to exchange data between the two contexts.

[Bharat Kasodariya]

You can share two applicatoin's context by corss context sharing. In tomcat you can do it by configuring crossContext attribute of Context tag.

If you are using tomcat, can Refer.
http://tomcat.apache.org/tomcat-5.5-doc/config/context.html. search for crossContext.

[lakshmana dhanimireddi]

If we set the crossContext property to true, we can only access the resources such as servlets,jsps,other files in other web app. But we can't access session object in other context. We can write resource(servlet or jsp) which gives the info'n about the session object in other context.

[Bharat Kasodariya]

You can access and set data with set/get Attribute in context of other app.

This post might be helpful for you
https://coderanch.com/t/560259/JSP/java/passing-session-values-between-two