Restriction on number of opened tabs

Question

There are some links on web-page.

On right click there is option of \'open link in new tab\'(browser option).

I want to restrict user for not opening more t

Answer 1

You can't restrict the user from opening a new tab.
_{(This reminds me the old pop-ups with no buttons, no address bar, but still responding to backspace and other events)}

You can however make your app recognize the attempt of opening a third tab, and load a different result like an error message, for example:

Maximum open tabs limit reached. Please use no more than two tabs concurrently. close this tab

To do this, you can use HTML5 sessionStorage.
_{Note: Web Storage (sessionStorage and localStorage) is supported on every browser nowadays.}

sessionStorage

This is a global object (sessionStorage) that maintains a storage area that's available for the duration of the page session. A page session lasts for as long as the browser is open and survives over page reloads and restores. Opening a page in a new tab or window will cause a new session to be initiated.

Then you can

• if not present in sessionStorage, generate an unique token in JSP, and put it in sessionStorage,

  $(function(){
      // Read the ID. If it's null, this is a new tab: 
      // generate the ID and store it for later.
      var tabId = sessionStorage.getItem("tabId");
      if (tabId == null){
          tabId = Math.random();
          sessionStorage.putItem("tabId",tabId);
      }
  

• send it back to the action

      // Add the ID to the form (as hidden field), 
      // so it will be posted back in next submission.
      $('').attr('type'  , 'hidden')
                  .attr('name'  , 'tabId')
                  .attr('value' , tabId)
      .appendTo('form');
  });
  

  , maybe to a setter in a BaseAction, extendend by the other actions, and read by prepare(), or much better in an Interceptor;

• put it in a collection checking that it doesn't contain already two elements, otherwise return the error result, that should be mapped globally:

  public String intercept(ActionInvocation actionInvocation) throws Exception {
      Action action = (Action) actionInvocation.getAction();
      if(action instanceof LimitedTabsAware){ //interface to identify special actions
          ActionContext context = actionInvocation.getInvocationContext();
          Map request = ((HttpServletRequest) 
                              context.get(StrutsStatics.HTTP_REQUEST)).getParameterMap();
  
          if (request.containsKey("tabId")){              
              String tabId = (String) request.get("tabId")[0];
              List openTabs = context.getSession().get("OPEN_TABS_KEY");
  
              if (openTabs.contains(tabId)){
                  return actionInvocation.invoke();                   
              } else if (openTabs.size()>=2){
                  return "tabLimitExceeded"; // global result
              } else {
                  openTabs.add(tabId);
                  context.getSession().put("OPEN_TABS_KEY", openTabs);
                  return actionInvocation.invoke();
              }
  
          } else {
              throw new IllegalArgumentException("There is no tabId in this request.");
          }
      } else {
          return actionInvocation.invoke();
      }
  }
  

Then you should find a way to recognize when a tab get closed (to free one slot), by either:

• timizing the period of validity of the elements in your collection (if you don't use a tab for some time, the session expires, and so must do the token in the collection)
• otherwise, putting a javascript AJAX timer in your page (eg. every 30 seconds), that send a keep-alive signal to an action to refresh the validity of the element. If the tab get closed, the signal is not sent anymore.