First Question:
Consider, I am filling any form then I refresh that page,what I want is what ever I fill in that page should not clear not only refresh page even if network problem occurred during filling the form.
Second Question:
If I login with any username and password then I fill in form and if network problem occurrs during filling the form then I go to another machine and login with same username password, I want whatever I entered In previous system should be show in this machine.
Sorry for my poor english, please tell any idea.
You should try and leverage client side storage. This will allow you to store the user data on the local browser. Here is an article on this http://www.html5rocks.com/en/tutorials/offline/storage/
I hope it helps
Fixing the following requires:
1 - Background worker on the client side that posts the data to the server .
Worker;
//or
window.setInterval();
2 - A banner or a status div showing the user that he is connected or disconnected.
var isOnline = window.navigator.onLine;
3 - Notify the user about reloading the page.
window.addEventListener("beforeunload", function (e) { alert('Your leaving...') });
Your first question has a pretty simple and straightforward solution: you'd want to save the data on the local machine, using something like cookies or localStorage.
For your second question, you'd need a much more complicated solution. Basically, you need to constantly persist the view data (input values, etc.) to the server for "safekeeping", since you assume the machine might crash at any given moment.
So your backend should support saving "temp form data", and whenever a user enters the relevant screen, you need to check for such temp form data on the backend, and populate the form accordingly. This will probably cause lots of edge cases and isn't trivial IMO.
Related
update post of screenshotsI've got an COM excel add-in (name; Syntess Atrium Office add-in) which has a login button. When pushed i need to give a path to it's location on the server and after that I need a password to log in.
I need to run this Excel file a couple of times each month late at night with a scheduled task, and every time I need to be logged-in for it to function. So to make sure i'm always logged-in I want to create either a VBA script or any other script to push the log-in button, write down the path, hit enter, and then use my password and hit enter again.
The application (VBA excel sheet) runs at night because it takes several hours to create because of it's huge amount of data it takes from our financial database on the server(using the com add-in).
I hope someone can help me out!
I know I can use programs like Acces or even Excel it self for a direct link with the database, but our directors won't allow this, so that's not an option unfortunately.
If you can view the reference in the object browser you can start to get an idea of the functions (if exposed) that you can use.
You can see from the image below that the class DOMDocument60 (XML Document Object Model) has a loadXML function that "loads the document from a string".
Normally you would not have to use the object viewer as this same information is generally provided by the company:
MSDN - MSXML3.0/6.0 - 'loadXML'
However, if there is no public API available you may be able to read through the object and get an understanding of what you can call.
---If you can't find a 'login' function your best bet is to ask the company to expose such a method (function).
Is it possible to send extra data attached to a http response via Java or Php?
My Website is a homework-platform: One User enters homeworks into a database, and all users can then see the homeworks on the website. The current load is very inefficient, as the browser makes two requests for eveything to load: One for the index file and one for the homeworks. For the homeworks request the client also sends settings of the user to the server, based on which the returned homeworks are generated by a Php script.
Now, I wonder, if it is possible, to combine those two requests into one? Is it maybe possible to detect the http request with Java or Php on the server, read the cookies (where the settings are saved), then get the homeworks from the database and send the data attached to the http response to the client? Or, even better, firstly only return the index file and as soon as possible and the homework data afterwards as a second response, because the client needs some time to parse the Html & build the DOM-tree when it can't show the homeworks anyway.
While browsing the web I stumbled across terms like "Server-side rendering" and "SPDY", but I don't know if those are the right starting points.
Any help is highly appreciated, as I'm personally very interested in a solution and it would greatly improve the load time of my website.
A simple solution to your problem is to initialize your data in the index file.
You would create a javascript object, and embed it right into the html, rendered by your server. You could place this object in the global namespace (such as under window.initData), so that it can be accessed by the code in your script.
<scipt>
window.initData = {
someVariable: 23,
}; // you could use json_encode if you use php, or Jackson if you use java
</script>
However, it is not a huge problem if your data is fetched in a separate server request. Especially when it takes more time to retrieve the data from the database/web services, you can provide better user experience by first fetching the static content very quickly and displaying a spinner while the (slower) data is being loaded.
Scenario:
We have one analysis which gives different results based on different inputs. So if the user open the same analysis in two different browser tabs, the session variables being common will get overridden and output will be same in both tabs though we want different outputs based on different user inputs in tabs.
So we plan to send a tab-id at the backend so that we save session variables per tab-id.
Is there some automatic way that tab information is being sent to the server like may be in request header or something like that??
Or we will have to generate a tab-id ourselves and send it with every request?
You'll have to generate your tab-id and pass it back with each request, but the following might make it a bit easier:
You can use sessionStorage from Web Storage API to store values unique to each tab. Every tab in the browser starts a new session so they are always distinct.
https://developer.mozilla.org/en/docs/Web/API/Window/sessionStorage
It should work with most common browsers (even IE8+): http://caniuse.com/#search=web%20storage
Hope that helps!
I understand that this question is asked over and over again, but I want a way to handle back button clicks on the server side (like banking applications).
When the user clicks on the back button, the page should be invalid and the user should be asked to start all over again.
Can you direct me to some tutorials on this?
The simplest way I've seen this solved is as follows.
Every page is served up with a unique ID/token.
That unique ID is always submitted when submitting any forms, and tracked on the server as being "used".
If the user ever clicks "back" and re-submits the same form, the server checks the unique ID... notices that it is a duplicate and then ignores the submission.
Note this won't physically stop a user from going "back", but if the last action was "transfer $1,000,000 dollars!" - the user won't accidentally transmit 2 million.
Make pages not cachable
track the user route server side, if she is visiting the visited page which she isn't supposed to revisit by back, in a session data may be.
check to see if she is requesting the visited resource then handle accordingly
Filter is the best place to do
Instruct page to use no cache.
Add to the head element of the page
<meta http-equiv="Pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
There are two problems you need to solve here.
The first is how browsers typically handle the back button. You should use a POST request to get to the page that the back button should not have access to. Most browsers will use a local cache for GET requests,, so if you do a GET, your server simply won't be accessed at all. A POST request will however typically perform a new request. Many browsers will also warn the user, and show a dialog box saying i.e. "Are you sure you want to send the form again?". So by using a POST, you increase the likelihood that every page load of that page will perform a new request to your server.
You may also be able to use a GET request where your server returns HTTP headers that makes browsers not load the page from the cache. Experiment with this.
The second problem is to make sure you invalidate duplicate requests server side. The first solution I can think of is to generate a token that you submit with the form and store in a database on every request. If a request is performed with a token that already is stored, you can invalidate the request. Perhaps there are better techniques, but I'll leave that as an exercise for the reader ;)
I also searched for this , and after all i found a little trick i think it may for your.
Every page your have an javaScript function that call to server with
ajax to check whether this page is available at that time.
In the server side you keep the availability (with the session).
If not redirect the page as you wish .
Say, you are submitting a form, which affects your database (adding records/ deleting them/ updating them) and this is how your request looks like:
POST /application/action=update
Now, say, you are done with your update, so you would like to take the user to the home page.
Response.sendRedirect /application/action=home
This works wonderfully well. User is sent a redirect after POST, so even if the user tries to refresh the page by hitting F5, you are good. However, this will not work if you did this:
requestDispatcher.forward(/application/action=home)
Given that there is a scenario where you have to display different kinds of error / success messages after you are done with your update, you are most likely doing a forward after POST. In such a scenario, how do you avoid update actions from happening twice?
I find it rather amusing that many secure sites (banks) / payment gateways tend to inform the user by placing text on screen, such as "Please don't press back / refresh buttons".
Is there no better way to handling this? Other than requesting the user not to press these buttons? When I last checked, there was something called the 'Vertical Response Cache'. A Filter that would identify uniqueness of your request in a session and tries to send a cached response if the request is duplicate. Are there any simpler ways to solving this classic problem?
Here is a link to the vertical response cache solution I was talking about: http://www.fingo.info/en/articles/_1.html. I am, However, not sure as to how well this really works.
Yes, I believe that you should redirect after a POST, with the exception of API requests. Without doing this not only do you have to worry about getting duplicate POSTs when the user uses the back button, but the browser will also give the user annoying dialogs when they try to use the back button.
Response.sendRedirect works in practice, but tecnically speaking this is sending the wrong HTTP response code for this purpose. sendRedirect sends a 302, but the correct code to use to transform a POST into a GET is 303. (most browsers will treat a 302 just like a 303 if they get it in response to a POST, however)
In general you want the redirect to send the user to whatever view will display the effect of their change. For example, if they edit a widget, they should be redirected to the view of that widget. If they delete a widget, they should be redirected to the view that the widget would have appeared in when it existed (perhaps the widget list).
Sometimes it's nice to have a status message to further drive home the fact that an action occurred. A simple way to do this is to have a common parameter to your views that, when set, will display an action completed message. eg:
/widget?id=12345&msg=Widget+modified.
Here the "msg" parameter contains the message "Widget modified". The one downside to this approach is that it may be possible for malicious sites to give your users confusing/misleading messages. eg:
/account?msg=Foo+Corp.+hates+you.
If you're really worried about this you could include an expiring signature for the message as an additional parameter. If the signature is invalid or has expired, simply don't display the message.
The best solution to solve the problem of showing status messages to the users after a POST to GET redirect is to use user sessions.
How
Add attributes to user session with value as set of messages to be displayed. for eg.
userSession.put("success_messages", new HashSet<String>(){"Success", "Check your account balance"});
userSession.put("warning_messages", new HashSet<String>(){"Your account balance is low. Recharge immediately"});
And have a filter which scans the user session for these particular attributes and outputs the messages. The filter should delete the attributes after reading once, as the status messages are generally displayed only once.
One thought that I've had is to embed a unique ID (probably a random string) as a hidden form field in the form that is being POST-submitted. The ID string can be put in the database as a "transaction ID". Now, when you go to update the database, first check whether there's an existing record with the submitted transaction ID, and if so, assume it's a duplicate and don't change the database.
Of course, as I said, this is just a thought. I don't know what methods are actually used in practice. (I suspect that a lot of less-critical sites just ignore the problem and hope their users will be smart... a losing proposition if I ever saw one ;-)
EDIT: as pointed out in the comments, storing transaction IDs in the database might take up a lot of space, but if that's an issue, you could keep an in-memory cache of all transaction IDs processed in the last 5 minutes/1 hour/1 day/whatever. That should work unless you're up against a determined hacker...
I find it rather amusing that many secure sites (banks) / payment gateways tend to inform the user by placing text on screen, such as "Please don't press back / refresh buttons".
some people find its better to "disable all Back, Refresh event on this critical pages";
I'm not sure if this is good or not.
But your addressed solution "vertical response cache" sounds nice
Its a little non-obvious but:
create a keyed-object in the user session.
the value is a Request + java Future for the result
return immediately with a client-side redirect.
while the client-side redirect is being handled, have a worker thread work on producing the answer.
So by the time the client browser completes the redirect, getting the new page's images, etc... the results are waiting for the user.
The alternative is to make the user painfully aware of how long the database is taking.
Security Update (2011 Jan 24 ) :
The key is vulnerable to attack since it is part of the response to the client, so
Generate a random key
Use user's session id as a salt to create a SHA-1
Store both the random key and the SHA-1 in the database with (, ) as the primary key. (no separate indexing on the RANDOMKEY.
Use both RANDOMKEY and the SHA-1 as the db lookup.
Do not store the Session Id (avoid privacy issues with being able to corollate many entries to the same user)
Expire the results after 2-3 days. ( Allows a daily batch job to do the clean up and avoids creating problems for user sessions that are semi-long lasting )
This method requires any hacker to know both the session id and the random key.
This approach may seem overkill, but a redirect-hardened mechanism can be used for situations like password resets.
If you are working with java server side scripting and also using struts 2 then you refer this link which talks about on using token .
http://www.xinotes.org/notes/note/369/
A token should be generated and kept in session for the initial page render, when the request is submitted along with the token for the first time , in struts action run a thread with thread name as the token id and run the logic whatever the client has requested for , when client submit again the same request, check whether the thread is still running(thread.getcurrentthread().interrupted) if still running then send a client redirect 503.
Please look at the ExecuteAndWaitInterceptor of struts 2code, the logic of this combined with token will help out fast click