Java - Count Difference in minutes

Question

• I have to count the difference in Minutes between these two Dates, but the Dates are overlapping.
• I have two date ranges: EventStart, EventEnd
• I've written a SQL Query before (see below) and it's working perfectly but its really slow, so I want to handle it in Java (resultSet)

Here is the JSON that I'm getting from SQL Server:

https://pastebin.com/raw/xhCnXynA

Here is my SQL script that is working:

DECLARE @T TABLE(ID INT,FromDate DATETIME, ToDate DATETIME)

INSERT INTO @T(ID,FromDate,ToDate)
SELECT 1,'20090801','20090803' UNION ALL
SELECT 2,'20090802','20090809' UNION ALL
SELECT 3,'20090805','20090806' UNION ALL
SELECT 4,'20090812','20090813' UNION ALL
SELECT 5,'20090811','20090812' UNION ALL
SELECT 6,'20090802','20090802'

SELECT ROW_NUMBER() OVER(ORDER BY s1.FromDate) AS ID,
       s1.FromDate,
       MIN(t1.ToDate) AS ToDate
FROM @T s1
INNER JOIN @T t1 ON s1.FromDate <= t1.ToDate
  AND NOT EXISTS(SELECT * FROM @T t2
                 WHERE t1.ToDate >= t2.FromDate
                   AND t1.ToDate < t2.ToDate)
WHERE NOT EXISTS(SELECT * FROM @T s2
                 WHERE s1.FromDate > s2.FromDate
                   AND s1.FromDate <= s2.ToDate)
GROUP BY s1.FromDate
ORDER BY s1.FromDate

Result:

My Java code:

//Date Format
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");   

Integer downTime;

while (rs.next()) {  

    //Parse to Date
    eventStart = formatter.parse(rs.getString("EventStart"));
    eventEnd = formatter.parse(rs.getString("EventEnd"));

    if (eventStart.after(eventEnd)){
         //How should I do this?
    }
    else{
         //How should I do this?
    }

    //I have to count here the difference between the dates in minutes
}  

Answer 1

Counting a difference in minutes between 2 dates

Better to use java.time.format.DateTimeFormatter and java.time.LocalDateTime from a New Java Date/Time API instead of SimpleDateFormat and Date:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.S");
LocalDateTime eventStart = LocalDateTime.parse("2019-10-09 01:24:05.0", formatter);
LocalDateTime eventEnd = LocalDateTime.parse("2019-10-09 01:35:14.0", formatter);
Duration duration;
if (eventStart.isBefore(eventEnd)) {
  duration = Duration.between(eventStart, eventEnd);
} else {
  duration = Duration.between(eventEnd, eventStart);
}
long minutes = duration.toMinutes();
System.out.println("" + minutes + " minute(s)");

The result is: 11 minute(s).

Merging all overlapping date ranges

To merge all overlapping date ranges consider the following approach.

Create a class to represent a date range with methods isOverlappingWith, mergeWith, toMinutes and override equals and hashCode.

private static class DateRange {

  private final LocalDateTime startDate;
  private final LocalDateTime endDate;

  public DateRange(LocalDateTime startDate, LocalDateTime endDate) {
    this.startDate = startDate;
    this.endDate = endDate;
  }

  public boolean isOverlappingWith(DateRange other) {
    return !startDate.isAfter(other.endDate) && !endDate.isBefore(other.startDate);
  }

  public DateRange mergeWith(DateRange other) {
    return new DateRange(
        startDate.isBefore(other.startDate) ? startDate : other.startDate,
        endDate.isAfter(other.endDate) ? endDate : other.endDate);
  }

  public long toMinutes() {
    return Duration.between(startDate, endDate).toMinutes();
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    DateRange dateRange = (DateRange) o;
    return Objects.equals(startDate, dateRange.startDate) &&
        Objects.equals(endDate, dateRange.endDate);
  }

  @Override
  public int hashCode() {
    return Objects.hash(startDate, endDate);
  }

  @Override
  public String toString() {
    return "DateRange{" +
        "startDate=" + startDate +
        ", endDate=" + endDate +
        '}';
  }
}

Iterate through all date ranges and try to merge them. To keep track of the duplicates additional HashSet is required. The idea is to try to merge each date range with next ranges in the list. If there were at least one merge then remove the original date range. If the list doesn't contain the resulting merged date range then append it to the list.

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.S");

List<List<String>> rawDateRanges = List.of(
    List.of("2009-08-01 00:00:00.0", "2009-08-03 00:00:00.0"),
    List.of("2009-08-05 00:00:00.0", "2009-08-06 00:00:00.0"),
    List.of("2009-08-02 00:00:00.0", "2009-08-09 00:00:00.0"),
    List.of("2009-08-12 00:00:00.0", "2009-08-13 00:00:00.0"),
    List.of("2009-08-11 00:00:00.0", "2009-08-12 00:00:00.0"),
    List.of("2009-08-02 00:00:00.0", "2009-08-02 00:00:00.0"));

List<DateRange> dateRanges = new ArrayList<>();
for (List<String> rawDateRange : rawDateRanges) { //Replace with while (rs.next()) { ... }
  LocalDateTime fromDate = LocalDateTime.parse(rawDateRange.get(0), formatter);
  LocalDateTime toDate = LocalDateTime.parse(rawDateRange.get(1), formatter);
  dateRanges.add(new DateRange(fromDate, toDate));
}

Set<DateRange> mergedDateRanges = new HashSet<>();
for (int i = 0; i < dateRanges.size(); i++) {
  DateRange dateRange = dateRanges.get(i);
  boolean merged = false;
  for (int j = i + 1; j < dateRanges.size(); j++) {
    DateRange otherDateRange = dateRanges.get(j);
    if (dateRange.isOverlappingWith(otherDateRange)) {
      dateRange = dateRange.mergeWith(otherDateRange);
      merged = true;
    }
  }
  if (merged) {
    dateRanges.remove(i--);
    if (mergedDateRanges.add(dateRange)) {
      dateRanges.add(dateRange);
    }
  }
}

List<Long> minutes = dateRanges.stream()
    .peek(System.out::println)
    .map(DateRange::toMinutes) //Convert to minutes
    .collect(toList());

System.out.println(minutes);

Output:

DateRange{startDate=2009-08-01T00:00, endDate=2009-08-09T00:00}
DateRange{startDate=2009-08-11T00:00, endDate=2009-08-13T00:00}
[11520, 2880]