Restriction on number of opened tabs

问题

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 that two tabs? How can i do this?

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<ul>
<li><a href="http://localhost:8080/struts_tab/abcForm1.action" oncontextmenu="return false;"><span>First Click[Right Click disabled]</span></a></li>
<li><a href="http://localhost:8080/struts_tab/defForm2.action"><span>Second clieck[Not more than 2 tabs]</span></a></li>
</ul>
</body>
</html>

回答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.
    $('<input>').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<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 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.

来源：https://stackoverflow.com/questions/30726627/restriction-on-number-of-opened-tabs

标签

javascript

jsp

web

struts2

browser-tab