failed to manipulate my Arraylist - spring

Question

I need help , I have an arrayList of objects . This object contains multiple fields I'm interested in this question by two date fields (date_panne date_mise and running) and two other time fields (heure_panne and time start),
And I would like to obtain the sum of the difference between (date_panne, heure_panne) and (date_mise_en_marche; heure_mise_en_marche) to give the total time of failure.
if someone can help me please I will be gratful this is my function :
public String disponibile() throws Exception {
int nbreArrets = 0;
List<Intervention> allInterventions = interventionDAO.fetchAllIntervention();
List<Intervention> listInterventions = new ArrayList<Intervention>();
for (Intervention currentIntervention : allInterventions) {
if (currentIntervention.getId_machine() == this.intervention.getId_machine()
&& currentIntervention.getDate_panne().compareTo(getProductionStartDate()) >= 0
&& currentIntervention.getDate_panne().compareTo(getProductionEndDate()) <= 0) {
listInterventions.add(currentIntervention);
}
}
savedInterventionList = listInterventions;
return "successView" ;
}

Answer 1

Assuming the the dates are truncated to the day and are of type java.util.Date, and that the times only contain hours, minutes, seconds and milliseconds and are also of type Date, start by creating a method like
private Date combine(Date dateOnly, Date timeOnly) {
Calendar dateCalendar = Calendar.getInstance();
dateCalendar.setTime(dateOnly);
Calendar timeCalendar = Calendar.getInstance();
timeCalendar.setTime(timeOnly);
dateCalendar.add(Calendar.HOUR_OF_DAY, timeCalendar.get(Calendar.HOUR_OF_DAY));
dateCalendar.add(Calendar.MINUTE, timeCalendar.get(Calendar.MINUTE));
dateCalendar.add(Calendar.SECOND, timeCalendar.get(Calendar.SECOND));
dateCalendar.add(Calendar.MILLISECOND, timeCalendar.get(Calendar.MILLISECOND));
return dateCalendar.getTime();
}
Now, it's simply a matter of looping through the interventions you want to sum, computing the difference between the dates as milliseconds, and add them:
long totalMillis = 0L;
for (Intervention intervention : interventions) {
Date marche = combine(intervention.getDateMiseEnMarche(), intervention.getTimeMiseEnMarche());
Date panne = combine(intervention.getDatePanne(), intervention.getTimePanne());
long differenceInMillis = marche.getTime() - panne.getTime();
totalMillis += differenceInMillis;
}