Scala in the browser : Scala.js.md

I gave a try to this scala to javascript compiler last night, and was quite amazed by the level of maturity this has already reached !

While probably never a replacement for mainline javascript in web sites, I see this as a competitor to coffeescript for web applications.

Full demo of scala-js-fiddle so you can experiment with scala directly in your browser, with some IDE-like features.

This implementation of Langton’s ant is what I achieved from scratch in 20 min.

Processing HTML with Scala as if XML

The controversial XML API for Scala is still usefull for simple use cases. However it comes short when dealing with HTML as found on public websites since it is not well formed.

	import java.net.URL
	import scala.xml.XML
	val site = new URL("http://michel-daviot.blogspot.fr/")
	XML.load(site)
	//Exception in thread "main" org.xml.sax.SAXParseException; lineNumber: 7; columnNumber: 265;
	//The entity name must immediately follow the '&' in the entity reference.

view raw XMLLoad.scala hosted with ❤ by GitHub

It is quite easy however to overcome this limitation by using the library tagsoup which allows to "fix" the HTML markup to make it look like XML.

You will add this dependency to your pom.xml :

	<dependency>
	<groupId>org.ccil.cowan.tagsoup</groupId>
	<artifactId>tagsoup</artifactId>
	<version>1.2.1</version>
	</dependency>

view raw pom.xml hosted with ❤ by GitHub

This simple object can then be used to load an URL containing HTML markup as if it was XML.

	import java.net.URL
	import scala.xml.XML
	import org.xml.sax.InputSource
	import scala.xml.parsing.NoBindingFactoryAdapter
	import org.ccil.cowan.tagsoup.jaxp.SAXFactoryImpl
	import java.net.HttpURLConnection
	import scala.xml.Node
	object HTML {
	lazy val adapter = new NoBindingFactoryAdapter
	lazy val parser = (new SAXFactoryImpl).newSAXParser
	def load(url: URL, headers: Map[String, String] = Map.empty): Node = {
	val conn = url.openConnection().asInstanceOf[HttpURLConnection]
	for ((k, v) <- headers)
	conn.setRequestProperty(k, v)
	val source = new InputSource(conn.getInputStream)
	adapter.loadXML(source, parser)
	}
	}

view raw HTML.scala hosted with ❤ by GitHub

Note that it also allows to set HTTP headers to the request, for instance if you want to use a cookie or a sessionId to get logged in.

Example calling code, which will list all HTML links from the loaded page :

	import java.net.URL
	val site = new URL("http://michel-daviot.blogspot.fr/")
	val content = HTML.load(site)
	for (
	a <- content \\ "a";
	href = a.attribute("href");
	if href.isDefined
	) println(href.get)

view raw HtmlDemo.scala hosted with ❤ by GitHub

And as a bonus, an object to force proxy settings from the code (for sure, you could also set it from the command line).

	object SetProxy {
	def apply(proxyConfig: (String, Int)) {
	val (host, port) = proxyConfig
	for (protocol <- Seq("http", "https")) {
	System.setProperty(s"$protocol.proxyPort", port.toString)
	System.setProperty(s"$protocol.proxyHost", host)
	}
	}
	}

view raw SetProxy.scala hosted with ❤ by GitHub