Couple of methods on how to parse an ISO 8601 duration expression in Java/Groovy.

parse_8601_durations_with_java.groovy

import javax.xml.datatype.*;  
Duration dur = DatatypeFactory.newInstance().newDuration("PT5H12M36S"); 

println dur.getHours()
println dur.getMinutes()
println dur.getSeconds()
println dur

println dur.getHours()*60*60 + dur.getMinutes()*60 + dur.getSeconds()


// ONLY WORKS ON JAVA 8!

java.time.Duration d = java.time.Duration.parse("PT5H12M36S");
println("Duration in seconds: " + d.get(java.time.temporal.ChronoUnit.SECONDS));