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Xml processing in scala
- 1. Basic XML Processing In Scala Neelkanth Sachdeva Consultant / Software Engineer Knoldus Software LLP , New Delhi neelkanthsachdeva.wordpress.com neelkanth@knoldus.com
- 2. What is XML ? → XML is a form of semi-structured data. → It is more structured than plain strings, because it organizes the contents of the data into a tree. → There are many forms of semi-structured data, but XML is the most widely used.
- 3. XML overview → XML is built out of two basic elements : 1. Text 2. Tags Text : As usual, any sequence of characters. Tags: Consist of a less-than sign,an alphanumeric label, and a greater than sign.
- 4. Writing XML Tags ● There is a shorthand notation for a start tag followed immediately by its matching end tag. ● Simply write one tag with a slash put after the tag’s label. Such a tag comprises an empty element. e.g <pod>Three <peas/> in the </pod> ● Start tags can have attributes attached to them. e.g <pod peas="3" strings="true"/>
- 5. XML literals Scala lets you type in XML as a literal anywhere that an expression is valid. Simply type a start tag and then continue writing XML content. The compile will go into an XML-input mode and will read content as XML until it sees the end tag matching the start tag you began with.
- 7. Important XML Classes Class Node is the abstract superclass of all XML node classes. Class Text is a node holding just text. For example, the “Here” part of <a>Here</a> is of class Text. Class NodeSeq holds a sequence of nodes.
- 10. Taking XML apart Extracting text : By calling the text method on any XML node you retrieve all of the text within that node, minus any element tags.
- 12. Extracting sub-elements : If you want to find a sub-element by tag name, simply call with the name of the tag: You can do a “deep search” and look through sub-sub-elements, etc., by using instead of the operator.
- 15. Extracting attributes: You can extract tag attributes using the same and methods. Simply put an at sign (@) before the attribute name:
- 18. Runtime Representation XML data is represented as labeled trees. You can conveniently create such labeled nodes using standard XML syntax. Consider the following XML document:
- 19. <html> <head> <title>Hello XHTML world</title> </head> <body> <h1>Hello world</h1> <p><a href="http://scala- lang.org/">Scala</a> talks XHTML</p> </body> </html> This document can be created by the following Scala program as :
- 20. object XMLTest1 extends Application { val page = <html> <head> <title>Hello XHTML world</title> </head> <body> <h1>Hello world</h1> <p><a href="scala-lang.org">Scala</a> talks XHTML</p> </body> </html>; println(page.toString()) }
- 21. It is possible to mix Scala expressions and XML : object XMLTest2 extends Application { import scala.xml._ val df = java.text.DateFormat.getDateInstance val dateString = df.format(new java.util.Date) def theDate(name: String) = <dateMsg addressedTo={ name }> Hello, { name }! Today is { dateString } </dateMsg>; println(theDate("Neelkanth Sachdeva").toString) }
- 22. Pattern matching on XML Sometimes we face a situation that there are multiple kinds of records within the data. In these kind of scenarios we used to go with pattern matching on XML.
- 23. object XMLTest3 { def search(node: scala.xml.Node): String = node match { case <a>{ contents }</a> => "It's an a Catagory Item & The Item Is : " + contents case <b>{ contents }</b> => "It's as b Catagory Item & The Item Is : " + contents case _ => "It's something else." } def main(args: Array[String]) { println(search(<a>Apple</a>)) println(search(<b>Mango</b>)) } }
- 24. Cheers