Web Scraping Ajax and Javascript Sites
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Introduction
Most crawling frameworks used for scraping cannot be used for Javascript or Ajax. Their scope is limited to those sites that show their main content without using scripting. One would also be tempted to connect a specific crawler to a Javascript engine but it’s not easy to do. You need a fully functional browser with good DOM support because the browser behavior is too complex for a simple connection between a crawler and a Javascript engine to work. There is a list of resources at the end of this article to explore the alternatives in more depth.
There are several ways to scrape a site that contains Javascript:
Embed a web browser within an application and simulate a normal user.
Remotely connect to a web browser and automate it from a scripting language.
Use special purpose add-ons to automate the browser
Use a framework/library to simulate a complete browser.
Each one of these alternatives has its pros and cons. For example using a complete browser consumes a lot of resources, especially if we need to scrape websites with a lot of pages.
In this post we’ll give a simple example of how to scrape a web site that uses Javascript. We will use the htmlunit library to simulate a browser. Since htmlunit runs on a JVM we will use Jython, an [excellent] programming language,which is a Python implementation in the JVM. The resulting code is very clear and focuses on solving the problem instead of on the aspects of programming languages.
Setting up the environment
Prerequisites
JRE or JDK.
Download the latest version of Jython from http://www.jython.org/downloads.html.
Run the .jar file and install it in your preferred directory (e.g: /opt/jython).
Download the htmlunit compiled binaries from: http://sourceforge.net/projects/htmlunit/files/.
Unzip the htmlunit to your preferred directory.
Crawling example
We will scrape the Gartner Magic Quadrant pages at: http://www.gartner.com/it/products/mq/mq_ms.jsp . If you look at the list of documents, the links are Javascript code instead of hyperlinks with http urls. This is may be to reduce crawling, or just to open a popup window. It’s a very convenient page to illustrate the solution.
gartner.py
01 import com.gargoylesoftware.htmlunit.WebClient as WebClient
02 import com.gargoylesoftware.htmlunit.BrowserVersion as BrowserVersion
03
04 def main():
05 webclient = WebClient(BrowserVersion.FIREFOX_3_6) # creating a new webclient object.
06 url = "http://www.gartner.com/it/products/mq/mq_ms.jsp"
07 page = webclient.getPage(url) # getting the url
08 articles = page.getByXPath("//table[@id='mqtable']//tr/td/a") # getting all the hyperlinks
09
10 for article in articles:
11 print "Clicking on:", article
12 subpage = article.click() # click on the article link
13 title = subpage.getByXPath("//div[@class='title']") # get title
14 summary = subpage.getByXPath("//div[@class='summary']") # get summary
15 if len(title) > 0 and len(summary) > 0:
16 print "Title:", title[0].asText()
17 print "Summary:", summary[0].asText()
18 # break
19
20 if __name__ == '__main__':
21 main()
run.sh
1 /opt/jython/jython -J-classpath "htmlunit-2.8/lib/*" gartner.py
Final notes
This article is just a starting point to move ahead of simple crawlers and point the way for further research. As this is a simple page, it is a good choice for a clear example of how Javascript scraping works.You must do your homework to learn to crawl more web pages or add multithreading for better performance. In a demanding crawling scenario a lot of things must be taken into account, but this is a subject for future articles.
If you want to be polite don’t forget to read the robots.txt file before crawling…
Resources
HtmlUnit
Crowbar web scraping environment
Google Chrome remote debugging shell from Python
Selenium web application testing system – Watir – Sahi – Windmill Testing Framework
Internet Explorer automation
jSSh Javascript Shell Server for Mozilla
http://trac.webkit.org/wiki/QtWebKit
Embedding Gecko
Opera Dragonfly
PyAuto: Python Interface to Chromum’s automation framework
Related questions on Stack Overflow
Scrapy
EnvJS: Simulated browser environment written in Javascript
Setting up Headless XServer and CutyCapt on Ubuntu
CutyCapt: Capture WebKit’s rendering of a web page.
Google webmaste blog: A spider’s view of Web 2.0
OpenQA
Python Webkit DOM Bindings
Berkelium Browser
uBrowser
Using HtmlUnit on .NET for Headless Browser Automation (using IKVM)
Zombie.js
PhantomJS
PyPhantomJS
Web Inspector Remote
Offscreen/Headless Mozilla Firefox (via @brutuscat)
Web Scraping with Google Spreadsheets and XPath
Web Scraping with YQL and Yahoo Pipes
Photo taken by xiffy
