In this article, we'll take a look at some advanced topics related to Kotlin and XML processing. We'll learn how to use Kotlin's built-in XML processing capabilities to perform common tasks such as validating XML, transforming XML, and querying XML.
It's important to validate XML before processing it to ensure that the XML is well-formed and that it adheres to any schema that may be required. Kotlin provides a number of ways to validate XML.
First, we can use the javax.xml.validation
API to validate XML against an XML Schema:
import javax.xml.XMLConstants
import javax.xml.validation.SchemaFactory
// Create a SchemaFactory capable of understand WXS schemas
val factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI)
// Load the specified schema
val schema = factory.newSchema(File("schema.xsd"))
// Create a Validator instance, which can be used to validate XML files
val validator = schema.newValidator()
// Validate the XML file
validator.validate(File("file.xml"))
Alternatively, we can use the kotlinx.xml.validation
library to validate XML against an XML Schema:
import kotlinx.xml.validation.Schema
import kotlinx.xml.validation.XmlValidator
// Load the specified schema
val schema = Schema.fromResource("schema.xsd")
// Create a validator
val validator = XmlValidator(schema)
// Validate the XML file
validator.validate(File("file.xml"))
In many cases, it's necessary to transform XML from one format to another. Kotlin provides a number of ways to transform XML.
First, we can use the javax.xml.transform
API to transform XML:
import javax.xml.transform.*
import javax.xml.transform.stream.StreamResult
// Create a TransformerFactory
val factory = TransformerFactory.newInstance()
// Use the factory to create a Transformer that will perform the transformation
val transformer = factory.newTransformer()
// Set the transformation parameters
transformer.setOutputProperty(OutputKeys.INDENT, "yes")
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2")
// Transform the XML
transformer.transform(
StreamSource(File("input.xml")),
StreamResult(File("output.xml"))
)
Alternatively, we can use the kotlinx.xml.transform
library to transform XML:
import kotlinx.xml.transform.*
// Transform the XML
transformXml("input.xml") {
declareDefaultNamespace("http://example.com/ns")
indent(2)
forEachElement("//*") {
println(it.name)
}
}.write("output.xml")
In many cases, it's necessary to query XML in order to extract specific information. Kotlin provides a number of ways to query XML.
First, we can use the javax.xml.xpath
API to query XML:
import javax.xml.xpath.*
// Create an XPathFactory
val factory = XPathFactory.newInstance()
// Use the XPathFactory to create an XPath object
val xpath = factory.newXpath()
// Compile an XPath expression
val expr = xpath.compile("//*[local-name()='root' and namespace-uri()='http://example.com/ns']")
// Evaluate the XPath expression in the context of the specified XML file
val node = expr.evaluate(File("file.xml"), XPathConstants.NODE)
// Print the result
println(node)
Alternatively, we can use the kotlinx.xml.xpath
library to query XML:
import kotlinx.xml.xpath.*
// Load the XML file
val xml = File("file.xml").readText()
// Parse the XML
val document = xml.parseXml()
// Evaluate the XPath expression
val node = document.evaluate("//*[local-name()='root' and namespace-uri()='http://example.com/ns']")
// Print the result
println(node)
In this article, we've taken a look at some advanced topics related to Kotlin and XML processing. We've learned how to use Kotlin's built-in XML processing capabilities to perform common tasks such as validating XML, transforming XML, and querying XML.