Set due date the timestamp class gives error

[Baris]

I'm currently working on script where I choose a customfield value and the due date will be set automatically

I get an error on the "Timestamp dueDateTimestamp = new Timestamp(myDueDate.getTimeInMillis())"  unable to resolve class timestamp.

What do I do wrong, what am I missing

import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.MutableIssue

// get value of valid period custom field
// LOGIC around what date is due date
// CALCULATION of due date
// INPUT the due date

def VALIDPERIOD = 10206 as Long

// def issue
def issue = ComponentAccessor.getIssueManager().getIssueByCurrentKey('MEG-24')
def dateToSet

//Get Managers
def CustomFieldManager = ComponentAccessor.getCustomFieldManager()

//Get Custom field Value
def ValidPeriodCustomField = CustomFieldManager.getCustomFieldObject(VALIDPERIOD)
def validPeriodValue = issue.getCustomFieldValue(ValidPeriodCustomField)

log.warn(validPeriodValue)

//Logic around what date
if (validPeriodValue == '30 Days') {
dateToSet = 30

}

else if (validPeriodValue == '60 Days') {
dateToSet = 60
}

else {
dateToSet = 90
}

log.warn('Date to set: ' + dateToSet + ' Line 40')

Calendar myDueDate = Calendar.getInstance()
myDueDate.add(Calendar.Date, dateToSet)

Timestamp dueDateTimestamp = new Timestamp(myDueDate.getTimeInMillis())

//input the calculated due date
issue.setDueDate(dueDateTimestamp)

log.warn ('New due date is: ' + dueDateTimestamp)

[Peter-Dave Sheehan]

I don't think you need to worry about timestamp and calendar classes.

Just use the built-in java dates. 

def dueDate = new Date()+dateToSet
def dueDateTimestamp = dueDate.toTimestamp()