The program I am writing is in Java.
I am writing a little program that will download the html of webpages and save them. It works easily for basic pages that don't use JavaScript. But how can I download the page if I want it after a script has updated it? The page I am dealing with is actually updated by Ajax which might be one step harder.
I understand that this is probably a difficult problem that involves setting up a JavaScript run time environment of some kind. I am prepared for a solution of any level of difficulty, I just don't know exactly how to approach it or where to get started.
You can't do that alone with Java only. As the page that you want to download is rendered with javascript, then you must be able to execute the javascript to get the whole rendered page.
Because of this situation, you need to use a headless browser which is a web browser that can access to web pages but can’t show the output within a GUI, aims to provide the content of web pages as fully rendered to serve to the programs or scripts.
You can start with the most famous ones which are Selenium, HtmlUnit and PhantomJS
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I am facing a problem retrieving the contents of an HTML page using java. I have described the problem below.
I am loading a URL in java which returns an HTML page.
This page uses javascript. So when I load the URL in the browser, a javascript function call occurs AFTER the page has been loaded (onBodyLoad of HTML page) and it modifies some content (one of the div id's innerHtml) on the webpage. This change is obviously visible to me in the browser.
Now, when I try to do the same thing using java, I only get the HTML content of the page , BEFORE the javascript call has occurred.
What I want to do is, fetch the contents of the html page after the javascript function call has occurred and all this has to be done using java.
How can I do this? What should my approach be?
You need to use a server side browser library that will also execute the JavaScript, so you can get the JavaScript updated DOM contents. The default browser mechanism doesn't do this, which is why you don't get the expected result.
You should try Cobra: Java HTML Parser, which will execute your JavaScript. See here for the download and for the documentation on how to use it.
Cobra:
It is Javascript-aware. DOM modifications that occur during parsing will be reflected in the resulting DOM. However, Javascript can be disabled.
For anyone reading this answer, Scott's answer above was a starting point for me. The Cobra project is long dead and cannot handle pages which use complex JavaScript.
However there is something called HTML Unit which does just exactly what I want.
Here is a small description:
HtmlUnit is a "GUI-Less browser for Java programs". It models HTML documents and provides an API that allows you to invoke pages, fill out forms, click links, etc... just like you do in your "normal" browser.
It has fairly good JavaScript support (which is constantly improving) and is able to work even with quite complex AJAX libraries, simulating either Firefox or Internet Explorer depending on the configuration you want to use.
It is typically used for testing purposes or to retrieve information from web sites.
I am trying to scrape a website, using Web Client, i am able to get the data on the first page and parse it, but I do not know how to read the data on the second page, the website is calling a java script to navigate to the second page. Can anyone suggest me how do I get the data from the next pages?
Thanks in advance
The problem you're going to have is while you (a person) can read the JavaScript in the first page and see it is navigating to another page, having the computer do this is going to be hard.
If you could identify the block of code performing the navigation, you would then need to execute it in such a way that allowed your program to extract the URL. This again is going to be very specific to the structure of the JavaScript and would require a person to identify this.
In short, I think you're dead in the water with this one, though it serves as a good example of why the Unobtrusive JavaScript concept is so important.
This framework integrates HtmlUnit with its headless javascript enabled browser to fully support scriping multiple pages in the same WebClient session: https://github.com/subes/invesdwin-webproxy
I'm not sure if this is possible but I would like to retrieve some data from a web page that uses Javascript to render data. This would be from a linux shell.
What I am able to do now:
http post using curl/lynx/wget to login and get headers from command line
use headers to get into 'secure' locations in the webpage on command line
However, the only elements that are rendered on the page are the static html. Most of the info I need are rendered dynamically with js (albeit eventually as a html as well) and don't show up on a command line browser. I understand the issue is with the lack of a js interpreter.
As such... some workarounds I thought might be possible are:
calling full browsers from command line and somehow passing the info back to stdout. this would mean that I have to be able to POST.
passing the headers (with session info, etc...) i got from curl to one of these full browsers and again dumping the output html back to stdout. it could very be a printscreen function on the window if all else fails.
a pure java solution would be OK too.
Anyone has any experience doing something similar and succeeding?
Thanks!
You can use WebDriver to do, just that you need have web browser installed. There are other solution as well such as Selenium and HtmlUnit (without browser but might behave differently).
You can find example of Selenium project at here.
WebDriver
WebDriver is a tool for writing automated tests of websites. It aims
to mimic the behaviour of a real user, and as such interacts with the
HTML of the application.
Selenium
Selenium automates browsers. That's it. What you do with that power is
entirely up to you. Primarily it is for automating web applications
for testing purposes, but is certainly not limited to just that.
Boring web-based administration tasks can (and should!) also be
automated as well.
HtmlUnit
HtmlUnit is a "GUI-Less browser for Java programs". It models HTML
documents and provides an API that allows you to invoke pages, fill
out forms, click links, etc... just like you do in your "normal"
browser.
I would recommend use WebDriver because it is not required standalone server like Selenium, while for HtmlUnit might suitable if you dont want install browser without worry about Xvfb in headless environment.
You might want to see what Selenium can do for you. It has numerous language drivers (Java included) that can be used to interact with the browser to process content typically for testing and verification purposes. I'm not exactly sure how you can get exactly what you are looking for out of it but wanted to make you aware of its existence and potential.
This is impossible unless you setup a websocket, and even like this I guess it really depends.
Could you detail your objective? For my personal curiosity :-)
I need to create a java program which should go to a website's login page, log in, than go to an another page of the site and submit a form. I know how to submit a form, but my problem is with the login part. This script should work with multiple sites, some are using cookies and some sessions. Is there any way to solve my problem ?
I can't show you any code because I don't know where to begin, first I should submit the login form and then separately go to the submission page ? I don't know please help me, or please tell me how could I solve this problem: I want to submit a form on various sites automatically, only I will be using this script. Until now I'we created a script in JavaScript and I'we opend the sites in iframes and I'we discovered that in Google chrome I can control external iframes, too, and I`we used JavaScript to fill the forms automatically, but my problem is that I need to submit files, images too, and I can't do this using only JavaScript. If it's not possible to do this using java please help me to find an another solution, I need to make it fully automated.
You can use Apache HTTP Client for logging in to websites using Java.
I would take a look at the Selenium RC framework and APIs. It's a test automation tool but there's no reason why you couldn't use it for doing programmatic logins to websites. It has client libraries for many languages including Java.
Using selenium RC you can write Java could thatcan load, navigate and fill in forms programmatically. You are able to target the form input fields using field names or classes and the Java API allows you to load multipart data into a form.
Selenium comes in two flavours, the older Selenium RC version and the newer WebDriver version. Both are capable of doing what you want, however they have slightly different ways of doing it. The documentation provides some good examples to get you started.
I need to screen scrape some data from a website, because it isn't available via their web service. When I've needed to do this previously, I've written the Java code myself using Apache's HTTP client library to make the relevant HTTP calls to download the data. I figured out the relevant calls I needed to make by clicking through the relevant screens in a browser while using the Charles web proxy to log the corresponding HTTP calls.
As you can imagine this is a fairly tedious process, and I'm wodering if there's a tool that can actually generate the Java code that corresponds to a browser session. I expect the generated code wouldn't be as pretty as code written manually, but I could always tidy it up afterwards. Does anyone know if such a tool exists? Selenium is one possibility I'm aware of, though I'm not sure if it supports this exact use case.
Thanks,
Don
I would also add +1 for HtmlUnit since its functionality is very powerful: if you are needing behaviour 'as though a real browser was scraping and using the page' that's definitely the best option available. HtmlUnit executes (if you want it to) the Javascript in the page.
It currently has full featured support for all the main Javascript libraries and will execute JS code using them. Corresponding with that you can get handles to the Javascript objects in page programmatically within your test.
If however the scope of what you are trying to do is less, more along the lines of reading some of the HTML elements and where you dont much care about Javascript, then using NekoHTML should suffice. Its similar to JDom giving programmatic - rather than XPath - access to the tree. You would probably need to use Apache's HttpClient to retrieve pages.
The manageability.org blog has an entry which lists a whole bunch of web page scraping tools for Java. However, I do not seem to be able to reach it right now, but I did find a text only representation in Google's cache here.
You should take a look at HtmlUnit - it was designed for testing websites but works great for screen scraping and navigating through multiple pages. It takes care of cookies and other session-related stuff.
I would say I personally like to use HtmlUnit and Selenium as my 2 favorite tools for Screen Scraping.
A tool called The Grinder allows you to script a session to a site by going through its proxy. The output is Python (runnable in Jython).