Web Scraping with JDK 8 ScriptEngine (Nashorn) and Scala

Web scraping is the process of extracting entities from web pages. This entities can either be news articles, blog posts, products, or any other information displayed on the web. Web pages consist of HTML (a XML like structure) and therefor present information in a structured form, in a DOM (Document Object Model), which can be extracted. The structure is usually not very strict or complaint to other web pages and object to change as the web page evolves. Using scripts over compiled programming languages has therefor a lot of advantages. On the other hand compiled languages have often a speed advantage as well as a broad foundation of fundamental libraries. The DOM reference implementation of the W3C is written in Java for example.

Java’s approach of opening up the JVM (Java Virtual Machine) for other (dynamically typed) languages is a great way to combine the benefits of both, a compiled and scripted language. With JDK 8 compiling dynamic languages to the JVM has become simpler with potentially improved implementations of compilers and runtime systems through the invokedynamic instruction. I found that this presentation currently explains best what invokedynamic is and how it works in general.

The language of the web is without doubt JavaScript. Fortunately the JDK 8 comes with a JavaScript implementation, which is called Nashorn and makes use of JSR 292 and invokedynamic. If you download the jdk you can simply get started with the jjs (JavaJavaScript) bin which is a REPL for Nashorn. To learn more about Nashorn you can read here, here, and here. In this post I would like to demonstrate how to use it for web scraping.

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Scala: Traits & Actors

Traits are Scala’s way of implementing mixins, which means to combine methods of other classes. It’s a powerful tool and an extension to the Java object model. You can think of Traits as Interfaces with concrete implementations.

The Actor model is a robust concurrency abstraction model that was introduced 1973 by Carl Hewitt, Peter Bishop, and Richard Steiger. A number of programming languages since then have adopted this model, probably most notably is the programming language Erlang. Since Erlang is widely used by the Telecommunications Industry or Facebook Chat the Actor model has already become the foundation of some of our day-to-day communication.

In this post I would like to give a brief overview of this two concepts applied in Scala by also providing some examples.

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