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What should i use to create web services app?

As an application to get a job I need to make a web app. I'm only familiar with Java SE so here comes my concerns. I need to make web service where at the beginning there will be authentication window, then I need to show the JSON data (probably parse it and show) as table or as list with button near to choose one of the row from the table to get to the next page where there user can choose a materials and so on.
I have data in JSON on server I need to pull it from there, then I need to show data which looks like this /materialDetails?ID=x where x is ID (it's probably HTTP or URI). Should I use Java REST? If yes I need to create a site in XML and then put java data inside? There're only a few tutorials on the internet and I can't find any good(sometimes the problem is in server, sometimes with dependencies). I was looking for information also on youtube but except https://www.youtube.com/watch?v=X36Dud8cS4Y I cant find anything useful? Could someone explain me this to make it at least a lil bit easier? Or just lead me to pick a specific framework. Thanks in advance

You could create a Dynamic Web Project with Tomcat and a MySQL Database for starters. You could use RESTEasy to create a WebService that gets data from your Database.
I don't know what exactly is expected from you, but this might be a good start. "Making a web app" is a bit like saying "I need to develop a java program", it is a bit vague !

I don't know REST but I think your application can be implemented with this technologies: HTML and Servlets/JSPs.
I would write an authentication page in HTML (one form element with 2 inputs and a button) which would pass credentials to a Java Server Page or a Servlet (they're equivalent). There I would build the table (another HTML element) thus producing a new HTML page.
P.S.: you're using JSON as a format so there's no need to learn XML.

Java Server-Side screen resolution detection

I'm building my own HTTP server in java, but i'm facing with a problem: I would like to build a page dynamically by creating every HTML object at runtime, the question is: how can i determine the screen dimension of the client's browser?
This information is not present in the HTTP header, so I was thinking about writing a "fake" webpage that runs a javascript that tells the server about the screen (it should redirect to something like www.website.com/w:1920,h:1080) but I don't know anything about cookies (that I suppose are essential to store those informations).
Do you think that I should learn somthng about cookies or there's another way?
BTW I'm not using servlets, just Socket, because that's what I know... should I use servlets?
Thanks for your time!
Matteo

Server knows nothing about client's screen until client send this information. Javascript is easiest way to determine screen size:
window.screen.availHeight
window.screen.availWidth
AJAX request can be used to send the information to the server where it can be stored in session data and backed in database for example if the user is logged in or identified somehow. In such case you don't need cookies. However solution with cookies is easier, check how to set them via javascript. But I'm afraid such solution would be a bit of non-standard, if your site is gonna depend on javascript why not to use it extensively and generate all objects on client side, get that lazy computer working and save your server's resources :) Just feed data by sending simplest HTML containing script doing the work.
Servlets? Can be really light-weight and done with minimal knowledge if you have time go for it.

How to generate different HTML based on the device that access the page?

I am using Java EE 6 with all the reference implementations and I wonder how you can generate different responses based on the device accessing the page? At the moment when I develop a JSF page I target browsers running on PC. However I want to generate another HTML structure (that is, using another JSF page) when the user browses the page with a smart phone.
Now you wonder, "Why doesn't you use CSS media queries?". Yes, I could but that will only give limited control over the layout. Could someone give me some hints to where and what to start reading about to do this?
I don't want to use Spring, I know they have something like this.

I don't want to use Spring, I know they have something like this.
Just reinvent it then (cough).
Let's look how they did it. According to the Spring Mobile documentation, cited below,
LiteDeviceResolver
The default DeviceResolver implementation is based on the "lite" detection algorithm implemented as part of the Wordpress Mobile Pack. This resolver only detects the presence of a mobile device and does not detect specific capabilities. No special configuration is required to enable this resolver, simply configure a default DeviceResolverHandlerInterceptor and it will be enabled for you.
it seems that they have ported this piece of PHP code to this piece of Java code. You could just do the same (be aware of license rules!). The most sensible place for this would be a servlet filter which would then send a redirect depending on the outcome of the detection.

I think you will need to look to the HTTP_USER_AGENT.
No experience with Java, but look to System.getEnv("HTTP_USER_AGENT").
It should return a string name for the user agent. You should find in the web lists of common user agents, so you can easily classify them as mobile or not mobile.

Inspect HTTP header
user-agent
you can retrieve this using Servlet API: http://docs.oracle.com/javaee/6/api/javax/servlet/http/HttpServletRequest.html#getHeader%28java.lang.String%29

How to fill out form data on a website

I am looking to develop an app that will take login details from the user, go to a website, login, return values on the web page and then display them to the user on the phone.
Does java have this functionallity? Will I need to use javascript instead maybe? do these answers depend on the website that I am trying to access?
In my head I figure that I could just read in the paramaters as strings or chars, parse the webpage for the appropriate form and "paste" the appropriate value into the form "box". However, I have never attempted anything like this with coding so I am completely new to the idea and dont really know where to start. I tried googling around but any information that I found was either irrelevant or conflicting.
I'm not looking for the code to do it because I will not really learn anythig from that but a finger in the right direction would be great. I really do want to try get better at programming so that's why I've started to give myself these little side projects
Any help that can be offered would be great

Ian,
You can try using http-client (http://hc.apache.org/httpclient-3.x/) lib from apache. It lets to pro grammatically access a website (from a Java code). You will need to do the following things
Use the http-client lib to POST the data to the web site.
Receive the html response.
Use some html parser or xpath to retrieve the values from the response html.

You would need a script which accesses the webpage and enters the data, but in my opinion this is illegal. Because you are accessing a secured area and are able to look into sensitive data. Also accessing the page via a script is "botting" - most pages have safety precautions to prevent the execution of scripts, because most of them are harmful.
In my opinion there is no legal and easy solution to this.

How can I open a webpage within a Java app and run my own javascript code

I would like to open a webpage and run a javascript code from within a java app.
For example I would like to open the page www.mytestpage.com and run the following javascript code:
document.getElementById("txtEmail").value="test#hotmail.com";
submit();
void(0);
This works in a browser...how can I do it programatically within a java app?
Thanks!

You can use Rhino to execute JavaScript but you won't have a DOM available - i.e. document.getElementById() would work.
You can use HTML Unit (headless) or WebDriver/Selenium (Driving a browser) to execute JavaScript in an environment that has a DOM available.

I'm not sure what you are looking for but I assume that you want to write automated POST request. This can be done in with Http Client library. Only you have to set appropriate request (POST or GET) parameters.
Look at examples - with this library you can do basic authentication or post files too.

Your question is a bit ambiguous, as we don't know the position of the Java program.
If that's a Java applet inside your page, you should look at Java<->JavaScript interaction, it works well.
If you need a separate Java program to control a browser, like sending a bookmarklet in the address bar (as one of your tags suggests), it is a bit harder (depends on target browser), perhaps look at the Robot class.

There's Rhino JS engine written in Java that you can run on app server such as Tomcat and feed JS to, however - it's not clear what are you trying to do with this?
There's also Envjs simulated browser environment which is based on Rhino but complete enough to run jQuery and/or Prototype

DWR (and other frameworks) now support "reverse ajax." The general idea is that you use one of three methods to communicate back to the client:
Comet (long-lived https session)
Polling
opportunistic / piggy-back (i.e. next time a request comes from the client, append your js call)
Regardless of method (which is typically a configuration-time decision and not a coding issue), you will have full access to any/all js calls you want to make.
Check out the reference page from DWR to get a pretty good explanation.