Limiting the number of open tabs

You cannot prevent a user from opening a new tab.
_{(This reminds me of old popups with no buttons, no address bar, but still responds to backspace and other events)}

However, you can make your application recognize the attempt to open a third tab and load a different result, such as an error message like:

The maximum allowed limit for open tabs has been reached. Use no more than two tabs at a time.close this tab

You can use HTML5 sessionStorage for this .
<sub>Note. Web storage ( sessionStorage

and localStorage

) is now supported in every browser .sub></sub>

sessionStorage

It is a global object ( sessionStorage

) that keeps the storage area available throughout the page session . The page session lasts as long as the browser is open and survives on the page reloads and restores. Opening the page in a new tab or window will result in a new session to be initiated .

Then you can

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

  $(function(){
      // Read the ID. If it 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 action

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

  maybe for a setter in BaseAction, expand with other actions and read prepare()
  
  or much better in Interceptor ;

• put it in the collection, making sure it doesn't already contain two elements, otherwise return the error result, which should be displayed 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<String, String[]> request = ((HttpServletRequest) 
                              context.get(StrutsStatics.HTTP_REQUEST)).getParameterMap();
  
          if (request.containsKey("tabId")){              
              String tabId = (String) request.get("tabId")[0];
              List<String> 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 must find a way to recognize when the tab is closed (to free up one slot), either:

• determining the expiration time of the items in your collection (if you don't use the tab for some time, the session will expire and therefore a token in the collection must be executed)
• otherwise a javascript AJAX timer on your page (for example every 30 seconds) that sends a signal keep-alive
  
  to an action to update the element's expiration date. If the tab is closed, the signal is no longer sent.