Formatting dates in java
Java 7
You can format the java.util.Date in Java 7 with java.text.SimpleDateFormat.
For example
SimpleDateFormat dateFormat = new SimpleDateFormat("dd/M/yyyy");
String formatedDate = dateFormat.format(new Date());
System.out.println("Formated date: " + formatedDate); // Formated date: 01/6/2018
Java 8
In Java 8 we can replace Date class with java.time.LocalDateTime and then use
java.time.format.DateTimeFormatter to format it.
You can notice that the date and time responsible classes are now inside of java.time package.
Example of formatting the date like for the same value as above.
LocalDateTime now = LocalDateTime.now();
DateTimeFormatter dateFormat = DateTimeFormatter.ofPattern("dd/M/yyy");
String formatedDate = LocalDateTime.now().format(dateFormat);
System.out.println("Formated date: " + formatDateTime); // Formated date: 01/6/2018
Patterns
Tip: Watch out! Patterns are case sensitive. In one application that I was working on, there were daily computational intensive exports running. The result files were then shared with partners. After some struggling why they can not parse the file we found out that date formatting on our side was wrong because we printed days in year instead days of month. To fix issue we had to change the pattern and rerun heavy jobs. To avoid formatting issues, if you want to print dates of the month the pattern is dd, the upper case DD stands for days in year.
| Letter | Date or Time Component | Presentation | Examples |
|---|---|---|---|
| D | Day in year | Number | 189 |
| d | Day in month | Number | 10 |
To compare result with an example above, in case we would write DD instead of dd the result would be following
SimpleDateFormat dateFormat = new SimpleDateFormat("DD/M/yyyy");
String formatedDate = dateFormat.format(new Date());
System.out.println(formatedDate); // 152/6/2018
You can test date formats quickly on online date formatter. Date time online formatter
It’s even better if you crete some JUnit tests for it.
Same goes for the year format. Dont use YYYY for formatting year but yyyy. Good article about it: https://www.juandebravo.com/2015/04/10/java-yyyy-date-format
Github Java project
You can check dates formatting in action in my java examples repository.
