Passing a closure as a binding property to generate an output string using string template engine

groovy

/* Snippet to pass a method as a closure to generate an output string */

import groovy.text.GStringTemplateEngine
import groovy.text.Template
import java.text.SimpleDateFormat

String formatDate(String date, String pattern, String timeZone){
    try {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern)
        simpleDateFormat.setTimeZone(TimeZone.getTimeZone(timeZone))

        return simpleDateFormat.format(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'").parse(date))
    } catch (Exception e) {
        println("Exception formatting the date ${date} using the pattern ${pattern} for timezone ${timeZone} - ${e}")
    }
    return date
}

GStringTemplateEngine engine = new GStringTemplateEngine()

List<Map> l = [
    ["pattern":"ddMMyy","timezone":"Europe/London","expected":"2020-08-20T00:43:23Z:190820"],
    ["pattern":"ddMMyyHH","timezone":"Europe/Madrid","expected":"2020-08-20T00:43:23Z:20082000"],
    ["pattern":"ddMMyyHHmm","timezone":"America/New_York","expected":"2020-08-20T00:43:23Z:1908201843"],
]

l.each { Map m ->
    String templateStr = '${params.date}:${formatDate.call(params.date, params.pattern, params.timezone)}'
    Map binding = ["params":["date":"2020-08-20T00:43:23Z", "timezone":m.get("timezone"), "pattern":m.get("pattern")], "formatDate":this.&formatDate]
    Map bindingDefaulted = binding?.findAll{it.value!=null}?.withDefault{ k -> defaultValue ?: '' }
    Template template = engine.createTemplate(templateStr)
    Writable result = template.make(bindingDefaulted)
    
    assert result.toString() == m.get("expected")
}