Converting Number representation of Date in excel

Question

I have date column in excel, but when I'm reading in my java application I'm getting value as number

Example

Excel Date

1/1/2013

Am getting as

41275.00

How to convert number to date in my Java application?

Answer 1

Excel’s serialized dates are the number of days since 1/1/1900. In order to figure out the date again, we have to add the serial number worth of days.

for Java 8 without any dependency

```

  /*

    1900-1-0            0
    1900-1-1            1
    1900-1-2            2
    1900-1-3            3


     */


    int days = 43323;
    LocalDate start = LocalDate.of(1900, 1, 1);
    LocalDate today = LocalDate.of(2018, 8, 11);


    // days to date
    LocalDate date = start.plusDays(days).minusDays(2);

    System.out.println(date);

    // date to days
    long days1 = ChronoUnit.DAYS.between(start, today) + 2;
    System.out.println(days1);

```

Answer 2

Here is a minimal working example how to convert an Excel date to a Java date:

        Date javaDate= DateUtil.getJavaDate((double) 41275.00);
        System.out.println(new SimpleDateFormat("MM/dd/yyyy").format(javaDate));

which returns

01/01/2013

You also need to import the following packages:

java.text.SimpleDateFormat
java.util.Date

Answer 3

Apache POI has some utilities for that http://poi.apache.org/apidocs/org/apache/poi/ss/usermodel/DateUtil.html, notably http://poi.apache.org/apidocs/org/apache/poi/ss/usermodel/DateUtil.html#getJavaDate(double)

Note Excel stores dates as the number of days (plus fractional days) since 1900 (and in some cases it can be from 1904). See http://support.microsoft.com/kb/180162.

Answer 4

tl;dr

Use modern java.time classes.

LocalDate                                    // Represent a date-only vaule, without time-of-day and without time zone.
.of( 1899 , Month.DECEMBER , 30 )            // Specify epoch reference date used by *some* versions of Excel. Beware: Some versions use a 1904 epoch reference. Returns a `LocalDate` object.
.plusDays(                                   // Add a number of days. 
    (long) Double.parseDouble( "41275.00" )  // Get a number of whole days from your input string.
)                                            // Returns another instance of a `LocalDate`, per Immutable Objects pattern, rather than altering the original.        
.toString()                                  // Generate text representing the value of this `LocalDate` in standard ISO 8601 format.

2013-01-01

java.time

The modern solution uses the java.time classes that supplanted the terrible legacy date-time classes bundled with the earliest versions of Java.

Epoch reference date: 1899-12-30

According to this documentation, that value from Microsoft Excel is the number of days since the epoch reference of 1900-01-01 in UTC. Internally, the actual reference date is December 30, 1899 as documented on this Wikipedia page.

Beware, some versions (old versions for macOS?) of Excel use a different epoch in 1904.

Establish the epoch reference somewhere in your code.

final static public LocalDate EXCEL_EPOCH_REFERENCE = 
    LocalDate.of( 1899 , Month.DECEMBER , 30 )
; // Beware: Some versions of Excel use a 1904 epoch reference.

Do the math

Parse your input string as a BigDecimal for accuracy (versus floating-point types that trade away accuracy for faster execution).

BigDecimal countFromEpoch = new BigDecimal( "41275.00" );

Add the number of whole days to the epoch reference date.

long days = countFromEpoch.longValue();  // Extract the number of whole days, dropping the fraction.
LocalDate localDate = EXCEL_EPOCH_REFERENCE.plusDays( days );

localDate.toString(): 2013-01-01

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.