如何从打开位置的其他JSP页面关闭文件

Question

I've a JSP page where a kind of users users_group_1 need to work with a file. All of them work with the same file , so since I'm in JSP, I made a class ( Class1 ) with all the methods as synchronized to avoid problems using it.

In the JSP for these group of users, I've only one instance for all them, declared like this:

<%!
  Class1 my_object = null;
%>

Then, when the first user uses the web, it does:

if (my_object == null)
{
  my_object = new Class1(file_to_open);
}

Then, all the users from the group will be using the same instance.

So now, I need another JSP page , that will be open by user_group_2 , to close this file and save the work done .

So I think I need to get the instance of Class1 used in the JSP and give it to the second one.

How can I do it?

Extra data: user_group_2 never uses the same JSP page than user_group_1 , so I can't use request/session/... objects (I think).

Answer 1

Your requirement can be achieved through something like given below by using ServletContext object(application scope).

On First jsp page where you want to initialize your object and set it to application scope.

<% 
     ProcessFile processFile=(ProcessFile)application.getAttribute("processFile");
     if(null==processFile){
     // make sure that all method of this class is synchronized beacause of multiple users
         processFile=new  ProcessFile("pathToOpenFile");
     }

     application.setAttribute("processFile", processFile); 
     //now processFile available globally. 
    %>

And after that on second jsp page you can use that processFile object which has been set into application scope like :

 <% 
        ProcessFile processFile2=(ProcessFile)application.getAttribute("processFile");
          // now start processing of file 
           if(null!=processFile2){

           processFile2.readFile();
          //open file if not. And read it.  

          //and after that. 
          processFile2.closeFileIfOpen();  
          // do neccesorry checks inside above method while closing file.  
          //all method are synchronized
          }
        %>

Answer 2

Create a singleton class and have everyone getting an instance of that class.

 public class SingletonFile {
      private static SingletonFile instance.
      static {
            instance = new SingletonFile();
      }

      public static SingletonFile getInstance() {
           return instance;
      }

      private SingletonFile () {}

      // public methods for manipulation of files goes here.
 }