打开标签的数量限制-前端问题

Restriction on number of opened tabs(打开标签的数量限制)

本文介绍了打开标签的数量限制的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

网页上有一些链接.

右键单击有在新选项卡中打开链接"选项(浏览器选项).

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

我想限制用户不要打开两个以上的标签?我该怎么做?

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>

推荐答案

您不能限制用户打开新标签页.
_{(这让我想起了没有按钮，没有地址栏，但仍然响应退格和其他事件的旧弹出窗口)}

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)}

但是，您可以让您的应用识别打开第三个标签页的尝试，并加载不同的结果(例如错误消息)，例如:

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:

已达到最大打开标签限制.请同时使用不超过两个选项卡.关闭此标签

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

为此，您可以使用 HTML5 sessionStorage.
_{注意:Web 存储(sessionStorage 和 localStorage)现在所有浏览器都支持.}

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

这是一个全局对象(sessionStorage)，维护一个存储区域在页面会话期间可用.页面会话只要浏览器打开并在页面上存活，就会持续重新加载和恢复.在新标签页或窗口中打开页面会导致将启动一个新会话.

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.

那你就可以了

如果sessionStorage中不存在，在JSP中生成一个唯一的token，放到sessionStorage中，

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);
    }

将其发送回操作

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');
});

，可能是 BaseAction 中的 setter，由其他操作扩展，并由 prepare() 读取，或者 在拦截器中更好；

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

把它放在一个集合中，检查它是否已经包含两个元素，否则返回错误结果，应该全局映射:

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();
    }
}

然后您应该找到一种方法来识别选项卡何时关闭(以释放一个插槽)，方法是:

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

优化集合中元素的有效期(如果您有一段时间不使用标签，会话过期，所以必须做集合中的令牌)
否则，在您的页面中放置一个 javascript AJAX 计时器(例如，每 30 秒)，发送一个 keep-alive 向动作发出信号以刷新元素的有效性.如果选项卡关闭，则不再发送信号.

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.

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