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Combine two http responses into one

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.

Request multiply parameters

I got a problem regarding request.getParameterMap()
In my jspx file multiply parameters are added when the user selects items out
of a table. now that i want to get them in my Controller
with request.getParameterMap(); it doesnt work with Firefox, Safari
but it works fine with chrome
anyone has an idea why it is so ?
thx for the replies .. the html form with the request parameters is build dynamicly at runtime using javascript, which seems to cause problems with widged based browsers like safari, firefox and most likely IE.
i will use ajax to get it work

The problem is not in the way that you are getting the parameter values from the map. It cannot be. The problem has to be in the HTML / Javascript / whatever that is creating the request on the client (browser) side.
It is most likely that you are doing something that is not strictly HTML (or whatever) compliant. Some browsers are treating it one way, and others another way. I suggest that you start by running an HTML validator over the page.

browser is not aware of request.getParameterMap() or any method in servlet api.
In your use case : you have a table of data , out of which user may select some rows and you need this data in server side for some action on those rows.
For eg : mark as read in GMAIL
select one or more rows in gmail and click ,mark as read will sent some request to google server and get those rows marked as read by user.
You can do it this way, you need to send primary key of your rows to server side with same parameter name
for eg: /delete?delId=1&delId=3&delId=7
and use request.getParameterValues() in server side to retrieve a list of ids to be deleted.

How to start a new session if a user click on the new tab in IE or mozilla on websphere portal?

I have one "user search" portlet on the home page of one application running on websphere portal server which displays the matching user records as per the search criteria filled in the search form. I have a requirement to have a "back to search input" link on the results page which on click should show the filled form on the input jsp.
The issue I am facing is if I open the application in two different tabs of same IE browser and start giving some search criteria and submit and at same time search for some other input from the other IE tab (in the same browser) and then go back to previous tab and click on "back to search input" link, instead of showing me the first input it will show me the input I entered in the next IE tab.
I am setting and getting the bean (form bean) through portlet session. But in the two diff tabs of the same IE it will be the same user session (and may be the same portlet session.)
How can I fix it so the two tabs save their search results independently?
The one thing to note here is I can access this "user search" application without logging in. So it must be taking the default portlet session in this case. What will happen once I login and then search; will it overwrite the portlet session and http session?

Basically your issue stems from the fact that your session is the same in both tabs so any data you store you can't expect to be different between tabs unless you store it as such. I would assign each search an id and store them in a collection in your session. Then when you draw your "back to search input" button add the search id such that you can pull the correct search out when building the input page.
Alternatively you could save server memory by posting the search as a query string on the return to search link rather than storing it in session.

What you describe is a fairly common problem faced by web app -- I think the official term is conversations -- which is the need to support something in-between the session scope and the request scope.
Some web framework support this concept, some not. The portlet specification does not support that out-of-the-box (Maybe there's something specific in websphere though).
I think one way to re-create the support for conversations, is to store a conversation id in the HTML generated. This way you can have an ID that is be per-tab / window. If suddenly a request receive an old ID, you know it comes from either an old page (if the user used the back button), or another tab.
That's ony a rough sketch. I'm pretty sure there a good resources on the web about this problem, otherwise spawn another question.

Do you always REDIRECT after POST? If yes, How do you manage it?

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

Multiple questions in Java (Validating URLs, adding applications to startup, etc.)

I have an application to build in Java, and I've got some questions to put.
Is there some way to know if one URL of a webpage is real? The user enters the URL and I have to test if it's real, or not.
How can I konw if one webpage has changes since one date, or what is the date of the last update?
In java how can I put an application running on pc boot, the application must run since the user turns on the computer.

I'm not sure what kind of application you want to build. I'll assume it's a desktop application. In order to check if a URL exists, you should make a HTTP HEAD Request, and parse the results. HEAD can be used to check if the page has been modified. In order for an application to start when the PC boots, you have to add a registry entry under Windows; this process is explained here

To check whether a url is valid you could try using a regular expression (regex for urls).
To know if a webpage has changed you can take a look at the http headers (reading http headers in java).
You can't make the program startup automatically on boot, the user must do that. However, you can write code to help the user set the program as startup app; this however depends on the operating system.

I'm not sure what you mean by "real". If you mean "valid", then you can just construct a java.net.URL from a String and catch the resulting MalformedURLException if it's not valid. If you mean that there's actually something there, you could issue an HTTP HEAD request like Geo says, or you could just retrieve the content. HTTPUnit is particularly handy for retrieving web content.
HTTP headers may indicate when the content has changed, as nan suggested above. If you don't want to count on that you can just retrieve the page and store it, or even better, store a hash of the page content. See DigestOutputStream for generating a hash. On a subsequent check for changes you would simply compare the new hash with the the one you stored last time.
Nan is right about start on boot. What OS are you targeting?