I am new in J2EE. Can anyone tell me:
What is one way to allow from a web page to start a long running server process but get an immediate response back?
Why are HTML checkboxes sometimes problematic for managing true/false values via form submissions?
Thanks in advance
1) It's called comet. This takes considerable resources because of the number of connections the server must keep open. This also sticks users to one server.
2) Programmer error.
Related
My company uses a shared MS Access database, with a back end stored on a server and a front end copied onto users desktops.
Recently, our IT department moved us to a new server without giving us any notice, and now our database keeps crashing.
Every 20-40 minutes, users get an error message that says:
Error 3043 Your network access was interrupted. To continue, close the database, and then open it again.
If they close and reopen, it does work. However, I'd like to stop this from happening, since it typically happens when they are in the middle of something and have to re-do everything.
I've already spoken with our IT consultants and they see no issue with our server/network, nor do they know anything about Access and therefore are no help.
Does anyone have any experience with this or have any ideas that may help me repair my database?
Thanks in advance.
Here are some thoughts:
It sounds very much like (short) network interruptions. MS Access doesn't like these at all, in particular it doesn't recover from a broken connection (even if very short) until you restart the frontend.
Network interruptions during write operations on Access backends are the prime cause of backend database corruption. Consider yourself lucky if you haven't experienced that yet. But you should backup and Compact&Repair the backend often (!) .
You can prevent backend corruptions by moving the backend to a server database, e.g. SQL Server Express (free). Errors will still occur ("ODBC call failed" instead of error 3043), but they will only affect the frontends.
You can probably work around all errors by changing the frontend from bound forms to unbound forms. This is a major undertaking.
I don't think there is anything you can do with the backend to prevent the errors.
If this database has value to your company, and IT says there is no problem, I suggest you escalate the problem to someone who can make IT look closer into the issue.
(How to do so would be a separate question, perhaps on SuperUser.)
I am working on a set of Classic ASP (VBScript) websites under different domains with 64bit Access (2013) database connection. Server is a shared Windows Server 2012 with IIS 8.5. The sites were not coded by me.
Everything seems to work fine for a time, but after several page calls (sometimes also at the first or only call to the site) the server does not respond for more than 20 to 30 seconds. This means: I can't call ANY page hosted on this server, even all other websites under different domains stop working for that time.
I am not sure, if plain HTML pages will respond, but it seems not. After such an issue everything is running fine again for various periods (up to 1 or 2 minutes), pages show up with normal response time, then this system hang repeats. And so on…
Finding the problem is extremely difficult, because all the sites on this shared hosting server could possibly cause this behaviour, it not necessarily seems to be triggered by my specific page call or subsequent calls, though it could be.
I am not sure, where to even look for the problem. I searched this forum and noticed some interesting answers, but not exactly to our problem. I tried Sysinternal's Process Monitor on a virtual server, where only one specific site is hosted and the same issues exists, but was not able to interpret most of the messages. I looked into event viewer log at this machine and noticed entries saying:
A trappable error (C0000005) occurred in an external object. The script cannot continue running.
But even if that sounds to be a possible reason, I am not sure where to look in the script or a log file, where I could find the trigger of all that. And on the shared host I don't even have the possibility to do that. On our local 'internal webserver' under Windows 10, where local copies of all the sites reside, I can. But I'm not sure, where to start my search.
Any help would be appreciated (and please don't needle me with proposals for switching to ASP.net or SQL - this is not possible at the moment).
I work with huge classic ASP application this error normally happens in a call for a Server.CreateObject('foo'). We have this kind of error here normally at the excel object when someone try to upload a very large .xls file. I would start mapping all the Server.CreateObject.
I've been having lots of problems getting my application to work using an sqlite database. Everything works just fine in ripple (I presume this is because it's just using chrome's sqlite implementation). However, once I run my app on a simulator (Curve 9300, OS 6) the problems begin. I've gotten to where the app can run, create a database, and insert rows, so I know that my actual queries are fine.
My application has a javascript file that has wrappers for working with the database. This javascript file is sourced in both the listener, and the page that is the core of the application. The problem is as follows:
Install the application. The listener starts running.
Send a text message from one simulator to another. The message is saved successfully (I can verify this because my banner indicator count increases, and the number is based of off a query)
Continue sending texts, and the banner indicator will increase.
Open the application, and read all of the messages. At this point, the javascript file is loaded twice, so I have two db objects pointing to the same database.
Close the application (listener is still running)
The next text message received causes a Runtime Exception, with no further details provided.
I looked at the stack trace, and it just says that the exception took place in the callback of the sms listener. This is obvious, as that's where the queries happen. Does anyone have any idea why opening a second connection to the db causes the exception? As far I understand, the db is only locked during a transaction. There are definitely no transactions running, other than the one trying to insert the new row. Although I'm new to javascript, I'm quite sure that no variables are being shared as the javascript file is loaded in two different pages. Any ideas would be greatly appreciated.
Well, I couldn't find a solution. I don't think the blackberry sqlite implementation can handle two concurrent connections. Instead, my listener now saves incoming data to a file. The file is read in when the main application opens, and all necessary data is saved to the db then. Afterwards, the file is deleted and the application performs queries without problem. I hope this helps anyone dealing with a similar issue.
I'm hoping this isn't harder than it seems.
I want to create an HTML form with a few text boxes that will allow people to enter in some data and I want these changes to be saved to the form.
For example, if my html page says:
Name: [ ]
...I want someone to be able to click on the [] and enter their name, etc. and click SAVE
and then have the form say:
Name: "Name of Person"
If someone wants to update that, they can click on the person's name and change it and click SAVE and have the HTML form update itself.
How can I do this? I've looked everywhere and people are talking about HTML5 AND PHP. Is it really that complicated to make a simple page like this?
(In case I wasn't clear in my html I'm using the contenteditable="true" option. How can I save those changes?)
I think your question indicates that you don't already know that web pages (including forms) are "stateless", meaning that they do not "automatically" hold or store anything that you do with them. Sorry to disappoint, but as a beginner you will struggle to find "an easy" solution to this.
That is not to say it can't be done - you no doubt see it everywhere - but your level of knowledge misses the fact that you need to actually program the logic to determine how your form will "appear" to store the information and reproduce it on a later visit.
Here's a (really) brief summary:
When your form is used by your user, a couple of things have already taken place before they get to see the form:
the user has requested the page (typing a URL or clicking a link)
the web server has sent the requested page (that is; your website has sent the form)
The next thing that takes place is that your user enters some data on the form. This data is not stored anywhere - if you refresh the page the data is gone, because steps 1 and 2 happen again.
So to avoid this you can use a number of tools:
Javascript: this operates on the user's computer. You can use it to find out if something has been entred on a form, and store it in, for example, a cookie.
Then you will have to build some logic into your page that says, "if my user refreshes the page or comes back to this site at a later date, then look for the cookie. If it exists, then take it's values and pre-fill the form, before the user gets to see it."
Server Side Script: This logic can be built into your web server (using a server side script like PHP) so it actually runs in step 2.
Alternatively you can build it into a javascript function which fires when the page is actually received by your user. This would be a step 3.
A second alternative combines these two ideas (processing on the user side and processing on the webserver side) called AJAX, which basically means that the "discussion" between your javascript and PHP takes place "on the fly" when the data is entered or changed.
And lastly you might want to consider PHP Sessions to store data, and/or a mySQL database. Recently with the advent of modern browsers you now have the possibility to store the information in a local database available to your user's browser...
In all of these cases you will need to learn how these pieces talk to each other, how you retreive the information, and how you update your stateless and static form.
It isn't has straightforward as you might think...
You don't need HTML5. HTML4 is good enough :)
But you need some server side script that saves the changes (on the server side in e.g. a DB or XML file). To make it a better experience (if multiple users use the form at the same time) I suggest you use AJAX to save the changes and poll the server for updates.
This is not complicated (at least I don't think it is), but it seems to be a generation ahead of what you already know. And it could take quite a long time to get the structure in place before you can do this sort of thing without needing help.
There are some basic questions
Does the information need to stay saved when the user hits reload?
Does the information need to stay saved when the user clears cookies?
If the information can be blanked out next time they come back to your page, then it is simple.
Otherwise, we need a way to keep track of which user sees what information, so the guy in Texas does not see the information the guy in Chinatown typed in. Cookies are a common way to do this. You could save the information to the cookies if there is not too much information.
Otherwise, you need sever-side language. This is usually in PHP, but deciding what language has to do with why you want to learn in the first place? Are you wanting to work for a company later on? Do you have your own website?
Please comment to let me know more what is going on, and what the answers are to the two basic questions, and I will better be able to answer.
Usually, for most cases, there is a login name and password (or OpenID), and if cookies are cleared, the user logs in again, but this requires some work to set up a working login before you re-visit this question of how to store what they type.
i have about 20 users who have their own access front end and write to a backend.
i need to do an update to the backend, and every time i try to do it offhours, it seems that someone is still logged on because the file is locked!
how do i get around this? i do tell the users to log off at the end of the day but a lot of them forget! is there a way to force them off?
can i disconnect someone from an access database?
Idle Detect/Inactivity Timeout
How to determine who is logged on to a database by using Microsoft Jet UserRoster in Access
I don't expect any points for my answer as Remou already gave you these. But whenever reasonable I prefer to give pages with links to the official KB articles rather thwn who knows how mangled up code can get in a forum. Including this one.