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Java - use searchbar on given website

Let me just start by saying that this is a soft question.
I am rather new to application development, and thus why I'm asking a question without presenting you with any actual code. I know the basics of Java coding, and I was wondering if anyone could enlighten me on the following topic:
Say I have an external website, Craigslist, or some other site that allows me to search through products/services/results manually by typing a query into a searchbox somewhere on the page. The trouble is, that there is no API for this site for me to use.
However I do know that http://sfbay.craigslist.org/search/sss?query=QUERYHERE&sort=rel points me to a list of results, where QUERYHERE is replaced by what I'm looking for.
What I'm wondering here is: is it possible to store these results in an Array (or List or some form of Collection) in Java?
Is there perhaps some library or external tool that can allow me to specify a query to search for, have it paste it in to a search-link, perform the search, and fill an Array with the results?
Or is what I am describing impossible without an API?

This depends, if the query website accepts returning the result as XML or JSON (usually with a .xml or .json at the end of url) you can parse it easily with DOM for XML on Java or download and use the JSONLibrary to parse a JSON.
Otherwise you will receive a HTML that is the page that a user would see in a browser, then you can try parse it as a XML but you will have a lot of work to map all fields in the HTML to get the list as you want.

How to integrate a part of one html website into java program?

Given a HTML website which displays a temperature outside and other unimportant peaces of information:
<div style="">15</div>
15 - is my destination number, which I want to extract as a variable.
Now what I want to do is, that Java program will go to the website, search for the particular HTML code line (temperature=15;) and after it is found, it must display it like this: http://i.stack.imgur.com/lY0qi.jpg
All I want to know, what syntax should I use to let program request that number.

Extracting information from a website is called crawling or scraping.
You basically go to the web site, get the HTML source and search it for your element. You can search with a regular expression or (more common) with a parser like Jsoup.
You will find a lot of working examples on the official site of Jsoup (e.g. http://jsoup.org/cookbook/extracting-data/example-list-links). Jsoup will parse the HTML source into a DOM-like structure with elements and nodes. You can search for specific nodes, e.g. for all DIV elements. Then you can iterate over them and get your temperature.

There are tools called scraper that extract information from the web .thare are many Java API that let you write your own scraper. You can try with JSoup ,HTMLUnit or Jaunt .

Extracting webpage information based on a template in Java

Right now I use Jsoup to extract certain information (not all the text) from some third party webpages, I do it periodically. This works fine until the HTML of certain webpage changes, this change leads to a change in the existing Java code, this is a tedious task, because these webpage change very frequently. Also it requires a programmer to fix the Java code. Here is an example of HTML code of my interest on a webpage:
<div>
<p><strong>Score:</strong>2.5/5</p>
<p><strong>Director:</strong> Bryan Singer</p>
</div>
<div>some other info which I dont need</div>
Now here is what I want to do, I want to save this webpage (an HTML file) locally and create a template out of it, like:
<div>
<p><strong>Score:</strong>{MOVIE_RATING}</p>
<p><strong>Director:</strong>{MOVIE_DIRECTOR}</p>
</div>
<div>some other info which I dont need</div>
Along with the actual URLs of the webpages these HTML templates will be the input to the Java program which will find out the location of these predefined keywords (e.g. {MOVIE_RATING}, {MOVIE_DIRECTOR}) and extract the values from the actual webpages.
This way I wouldn't have to modify the Java program every time a webpage changes, I will just save the webpage's HTML and replace the data with these keywords and rest will be taken care by the program. For example in future the actual HTML code may look like this:
<div>
<div><b>Rating:</b>**1/2</div>
<div><i>Director:</i>Singer, Bryan</div>
</div>
and the corresponding template will look like this:
<div>
<div><b>Rating:</b>{MOVIE_RATING}</div>
<div><i>Director:</i>{MOVIE_DIRECTOR}</div>
</div>
Also creating these kind of templates can be done by a non-programmer, anyone who can edit a file.
Now the question is, how can I achieve this in Java and is there any existing and better approach to this problem?
Note: While googling I found some research papers, but most of them require some prior learning data and accuracy is also a matter of concern.

The approach you gave is pretty much similar to the Gilbert's except
the regex part. I don't want to step into the ugly regex world, I am
planning to use template approach for many other areas apart from
movie info e.g. prices, product specs extraction etc.
The template you describe is not actually a "template" in the normal sense of the word: a set static content that is dumped to the output with a bunch of dynamic content inserted within it. Instead, it is the "reverse" of a template - it is a parsing pattern that is slurped up & discarded, leaving the desired parameters to be found.
Because your web pages change regularly, you don't want to hard-code the content to be parsed too precisely, but want to "zoom in" on its' essential features, making the minimum of assumptions. i.e. you want to commit to literally matching key text such as "Rating:" and treat interleaving markup such as"<b/>" in a much more flexible manner - ignoring it and allowing it to change without breaking.
When you combine (1) and (2), you can give the result any name you like, but IT IS parsing using regular expressions. i.e. the template approach IS the parsing approach using a regular expression - they are one and the same. The question is: what form should the regular expression take?
3A. If you use java hand-coding to do the parsing then the obvious answer is that the regular expression format should just be the java.util.regex format. Anything else is a development burden and is "non-standard" and will be hard to maintain.
3B. If you use want to use an html-aware parser, then jsoup is a good solution. Problem is you need more text/regular expression handling and flexibility than jsoup seems to provide. It seems too locked into specific html tags and structures and so breaks when pages change.
3C. You can use a much more powerful grammar-controlled general text parser such as ANTLR - a form of backus-naur inspired grammar is used to control the parsing and generator code is inserted to process parsed data. Here, the parsing grammar expressions can be very powerful indeed with complex rules for how text is ordered on the page and how text fields and values relate to each other. The power is beyond your requirements because you are not processing a language. And there's no escaping the fact that you still need to describe the ugly bits to skip - such as markup tags etc. And wrestling with ANTLR for the first time involves educational investment before you get productivity payback.
3D. Is there a java tool that just uses a simple template type approach to give a simple answer? Well a google search doesn't give too much hope https://www.google.com/search?q=java+template+based+parser&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-GB:official&client=firefox-a. I believe that any attempt to create such a beast will degenerate into either basic regex parsing or more advanced grammar-controlled parsing because the basic requirements for matching/ignoring/replacing text drive the solution in those directions. Anything else would be too simple to actually work. Sorry for the negative view - it just reflects the problem space.
My vote is for (3A) as the simplest, most powerful and flexible solution to your needs.

Not really a template-based approach here, but jsoup can still be a workable solution if you just externalize your Selector queries to a configuration file.
Your non-programmer doesn't even have to see HTML, just update the selectors in the configuration file. Something like SelectorGadget will make it easier to pick out what selector to actually use.

How can I achieve this in Java and is there any existing and better approach to this problem?
The template approach is a good approach. You gave all of the reasons why in your question.
Your templates would consist of just the HTML you want to process, and nothing else. Here's my example based on your example.
<div>
<p><strong>Score:</strong>{MOVIE_RATING}</p>
<p><strong>Director:</strong>{MOVIE_DIRECTOR}</p>
</div>
Basically, you would use Jsoup to process your templates. Then, as you use Jsoup to process the web pages, you check all of your processed templates to see if there's a match.
On a template match, you find the keywords in the processed template, then you find the corresponding values in the processed web page.
Yes, this would be a lot of coding, and more difficult than my description indicates. Your Java programmer will have to break this description down into simpler and simpler tasks until she or he can code the tasks.

If the web page changes frequently, then you'll probably want to confine your search for the fields like MOVIE_RATING to the smallest possible part of the page, and ignore everything else. There are two possibilities: you could either use a regular expression for each field, or you could use some kind of CSS selector. I think either would work and either "template" can consist of a simple list of search expressions, regex or css, that you would apply. Just roll through the list and extract what you can, and fail if some particular field isn't found because the page changed.
For example, the regex could look like this:
"Score:"(.)*[0-9]\.[0-9]\/[0-9]
(I haven't tested this.)

Or you can try different approach, using what i would call 'rules' instead of templates: for each piece of information that you need from the page, you can define jQuery expression(s) that extracts the text. Often when page change is small, the same well written jQuery expressions would still give the same results.
Then you can use Jerry (jQuery in Java), with the almost the same expressions to fetch the text you are looking for. So its not only about selectors, but you also have other jQuery methods for walking/filtering the DOM tree.
For example, rule for some Director text would be (in sort of sudo-java-jerry-code):
$.find("div#movie").find("div:nth-child(2)")....text();
There could be more (and more complex) expressions in the rule, spread across several lines, that for example iterate some nodes etc.
If you are OO person, each rule may be defined in its own implementation. If you are groovy person, you can even rewrite rules when needed, without recompiling your project, and still being in java. Etc.
As you see, the core idea here is to define rules how to find your text; and not to match to patterns as that may be fragile to minor changes - imagine if just a space has been added between two divs:). In this example of mine, I've used jQuery-alike syntax (actually, it's Jerry-alike syntax, since we are in Java) to define rules. This is only because jQuery is popular and simple, and known by your web developer too; at the end you can define your own syntax (depending on parsing tool you are using): for example, you may parse HTML into DOM tree and then write rules using your helper methods how to traverse it to the place of interest. Jerry also gives you access to underlaying DOM tree, too.
Hope this helps.

I used the following approach to do something similar in a personal project of mine that generates a RSS feed out of here the leading real estate website in spain.
Using this tool I found the rented place I'm currently living in ;-)
Get the HTML code from the page
Transform the HTML into XHTML. I used this this library I guess there might be today better options available
Use XPath to navigate the XHTML to the information you're interesting in
Of course every time they change the original page you will have to change the XPath expression. The other approach I can think of -semantic analysis of the original HTML source- is far, far beyond my humble skills ;-)

How can I extract only the main textual content from an HTML page?

Update
Boilerpipe appears to work really well, but I realized that I don't need only the main content because many pages don't have an article, but only links with some short description to the entire texts (this is common in news portals) and I don't want to discard these shorts text.
So if an API does this, get the different textual parts/the blocks splitting each one in some manner that differ from a single text (all in only one text is not useful), please report.
The Question
I download some pages from random sites, and now I want to analyze the textual content of the page.
The problem is that a web page have a lot of content like menus, publicity, banners, etc.
I want to try to exclude all that is not related with the content of the page.
Taking this page as example, I don't want the menus above neither the links in the footer.
Important: All pages are HTML and are pages from various differents sites. I need suggestion of how to exclude these contents.
At moment, I think in excluding content inside "menu" and "banner" classes from the HTML and consecutive words that looks like a proper name (first capital letter).
The solutions can be based in the the text content(without HTML tags) or in the HTML content (with the HTML tags)
Edit: I want to do this inside my Java code, not an external application (if this can be possible).
I tried a way parsing the HTML content described in this question : https://stackoverflow.com/questions/7035150/how-to-traverse-the-dom-tree-using-jsoup-doing-some-content-filtering

Take a look at Boilerpipe. It is designed to do exactly what your looking for, remove the surplus "clutter" (boilerplate, templates) around the main textual content of a web page.
There are a few ways to feed HTML into Boilerpipe and extract HTML.
You can use a URL:
ArticleExtractor.INSTANCE.getText(url);
You can use a String:
ArticleExtractor.INSTANCE.getText(myHtml);
There are also options to use a Reader, which opens up a large number of options.

You can also use boilerpipe to segment the text into blocks of full-text/non-full-text, instead of just returning one of them (essentially, boilerpipe segments first, then returns a String).
Assuming you have your HTML accessible from a java.io.Reader, just let boilerpipe segment the HTML and classify the segments for you:
Reader reader = ...
InputSource is = new InputSource(reader);
// parse the document into boilerpipe's internal data structure
TextDocument doc = new BoilerpipeSAXInput(is).getTextDocument();
// perform the extraction/classification process on "doc"
ArticleExtractor.INSTANCE.process(doc);
// iterate over all blocks (= segments as "ArticleExtractor" sees them)
for (TextBlock block : getTextBlocks()) {
// block.isContent() tells you if it's likely to be content or not
// block.getText() gives you the block's text
}
TextBlock has some more exciting methods, feel free to play around!

There appears to be a possible problem with Boilerpipe. Why?
Well, it appears that is suited to certain kinds of web pages, such as web pages that have a single body of content.
So one can crudely classify web pages into three kinds in respect to Boilerpipe:
a web page with a single article in it (Boilerpipe worthy!)
a web with multiple articles in it, such as the front page of the New York times
a web page that really doesn't have any article in it, but has some content in respect to links, but may also have some degree of clutter.
Boilerpipe works on case #1. But if one is doing a lot of automated text processing, then how does one's software "know" what kind of web page it is dealing with? If the web page itself could be classified into one of these three buckets, then Boilerpipe could be applied for case #1. Case #2 is a problem, and case#3 is a problem as well - it might require an aggregate of related web pages to determine what is clutter and what isn't.

You can use some libs like goose. It works best on articles/news.
You can also check javascript code that does similar extraction as goose with the readability bookmarklet

My first instinct was to go with your initial method of using Jsoup. At least with that, you can use selectors and retrieve only the elements that you want (i.e. Elements posts = doc.select("p"); and not have to worry about the other elements with random content.
On the matter of your other post, was the issue of false positives your only reasoning for straying away from Jsoup? If so, couldn't you just tweak the number of MIN_WORDS_SEQUENCE or be more selective with your selectors (i.e. do not retrieve div elements)

http://kapowsoftware.com/products/kapow-katalyst-platform/robo-server.php
Proprietary software, but it makes it very easy to extract from webpages and integrates well with java.
You use a provided application to design xml files read by the roboserver api to parse webpages. The xml files are built by you analyzing the pages you wish to parse inside the provided application (fairly easy) and applying rules for gathering the data (generally, websites follow the same patterns). You can setup the scheduling, running, and db integration using the provided Java API.
If you're against using software and doing it yourself, I'd suggest not trying to apply 1 rule to all sites. Find a way to separate tags and then build per-site

You're looking for what are known as "HTML scrapers" or "screen scrapers". Here are a couple of links to some options for you:
Tag Soup
HTML Unit

You can filter the html junk and then parse the required details or use the apis of the existing site.
Refer the below link to filter the html, i hope it helps.
http://thewiredguy.com/wordpress/index.php/2011/07/dont-have-an-apirip-dat-off-the-page/

You could use the textracto api, it extracts the main 'article' text and there is also the opportunity to extract all other textual content. By 'subtracting' these texts you could split the navigation texts, preview texts, etc. from the main textual content.

Java library for detecting list items on webpages

Most of the webpages now-a-days contain lists of things, or chunks of html patterns that repeat a lot.
For example:
Facebook status messages on homepages.
Digg/Hacker News
StackOverflow homepage
Is there a Java library for detecting such lists. It will involve some amount of pattern matching and intelligence. Thanks.

Between XPath expressions and HTML element "id" attributes you should be able to find the root of the lists you are interested in, and then more XPath will let you iterate over them.
If you don't have XPath already, I recommend using HtmlUnit. Yeah, it's meant for testing, but it works really well as "headless" browser and has excellent support for XPath-ing your way around the DOM of a page.

You might want to investigate the term 'scraper' on google. Pin-point extraction of data from web-pages is loosely called scraping as opposed to capturing the whole page 'crawling'.