Sub-Issue of 2753: Add new Patterns to JabRef's Date class and write tests.

[ThiloteE]

To solve this issue, one needs to add new Patterns to JabRef's Date class and write tests.

jabref/src/main/java/org/jabref/model/entry/Date.java

Lines 17 to 49 in 3759561

	public class Date {
	private static final DateTimeFormatter NORMALIZED_DATE_FORMATTER = DateTimeFormatter.ofPattern("uuuu[-MM][-dd]");
	private static final DateTimeFormatter SIMPLE_DATE_FORMATS;
	static {
	List<String> formatStrings = Arrays.asList(
	"uuuu-MM-dd'T'HH:mm[:ss][xxx][xx][X]", // covers 2018-10-03T07:24:14+03:00
	"uuuu-MM-dd'T'HH:m[:ss][xxx][xx][X]", // covers 2018-10-03T17:2
	"uuuu-MM-dd'T'H:mm[:ss][xxx][xx][X]", // covers 2018-10-03T7:24
	"uuuu-MM-dd'T'H:m[:ss][xxx][xx][X]", // covers 2018-10-03T7:7
	"uuuu-MM-dd'T'HH[:ss][xxx][xx][X]", // covers 2018-10-03T07
	"uuuu-MM-dd'T'H[:ss][xxx][xx][X]", // covers 2018-10-03T7
	"uuuu-M-d", // covers 2009-1-15
	"uuuu-M", // covers 2009-11
	"d-M-uuuu", // covers 15-1-2012
	"M-uuuu", // covers 1-2012
	"M/uuuu", // covers 9/2015 and 09/2015
	"M/uu", // covers 9/15
	"MMMM d, uuuu", // covers September 1, 2015
	"MMMM, uuuu", // covers September, 2015
	"d.M.uuuu", // covers 15.1.2015
	"uuuu.M.d", // covers 2015.1.15
	"uuuu", // covers 2015
	"MMM, uuuu"); // covers Jan, 2020
	SIMPLE_DATE_FORMATS = formatStrings.stream()
	.map(DateTimeFormatter::ofPattern)
	.reduce(new DateTimeFormatterBuilder(),
	DateTimeFormatterBuilder::appendOptional,
	(builder, formatterBuilder) -> builder.append(formatterBuilder.toFormatter()))
	.toFormatter(Locale.US);
	}

The order of the date patterns seem to matter as well, as I recently learned when extending the class to support Timestamps. The longest? pattern needs to come first.

See Section 2.3.9 of the biblatex manual http://mirrors.ibiblio.org/CTAN/macros/latex/contrib/biblatex/doc/biblatex.pdf

Originally posted by @Siedlerchr in #2753 (comment)

[ThiloteE]

closing, because outdated.