Add parser for German months (#3536)

CHANGELOG.md

@@ -34,6 +34,7 @@ The new default removes the linked file from the entry instead of deleting the f
 - The group editing window can now also be called by double-clicking the group to be edited. [koppor#277](https://github.com/koppor/jabref/issues/277)
 - The magnifier icon at the search shows the [search mode](https://help.jabref.org/en/Search#search-modes) again. [#3535](https://github.com/JabRef/jabref/issues/3535)
 - We added a new cleanup operation that replaces ligatures with their expanded form. [#3613](https://github.com/JabRef/jabref/issues/3613)
+- We added the function to parse German month names. [#3536](https://github.com/JabRef/jabref/pull/3536)
 
 ### Fixed
 - We fixed several performance problems with the management of journal abbreviations [#3323](https://github.com/JabRef/jabref/issues/3323)

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

@@ -1,5 +1,9 @@
 package org.jabref.model.entry;
 
+import java.time.YearMonth;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.util.Locale;
 import java.util.Optional;
 
 import org.jabref.model.strings.StringUtil;
@@ -85,9 +89,13 @@ public static Optional<Month> parse(String value) {
             testString = testString.substring(0, 3);
         }
         Optional<Month> month = Month.getMonthByShortName(testString);
+        Optional<Month> monthGerman = Month.parseGermanShortMonth(testString);
         if (month.isPresent()) {
             return month;
         }
+        if (monthGerman.isPresent()) {
+            return monthGerman;
+        }
 
         try {
             int number = Integer.parseInt(value);
@@ -97,6 +105,29 @@ public static Optional<Month> parse(String value) {
         }
     }
 
+    /**
+     * Parses a month having the string in German standard form such as
+     * "Oktober" or in German short form such as "Okt"
+     * 
+     * @param value,
+     *            a String that represents a month in German form
+     * @return the corresponding month instance, empty if input is not in German
+     *         form
+     */
+	private static Optional<Month> parseGermanShortMonth(String value) {
+        if ("Mae".equals(value)) {
+            return Month.getMonthByNumber(3);
+        }
+
+        try {
+            YearMonth yearMonth = YearMonth.parse("1969-" + value, 
+            		DateTimeFormatter.ofPattern("yyyy-MMM", Locale.GERMAN));
+            return Month.getMonthByNumber(yearMonth.getMonthValue());
+        } catch (DateTimeParseException e) {
+            return Optional.empty();
+        }
+    }
+
     /**
      * Returns the name of a Month in a short (3-letter) format. (jan, feb, mar, ...)
      *

src/test/java/org/jabref/model/entry/MonthTest.java

@@ -100,4 +100,38 @@ public void parseReturnsEmptyOptionalForInvalidInput() {
     public void parseReturnsEmptyOptionalForEmptyInput() {
         assertEquals(Optional.empty(), Month.parse(""));
     }
+
+    @Test
+    public void parseCorrectlyByShortNameGerman() {
+        assertEquals(Optional.of(Month.JANUARY), Month.parse("Jan"));
+        assertEquals(Optional.of(Month.FEBRUARY), Month.parse("Feb"));
+        assertEquals(Optional.of(Month.MARCH), Month.parse("M�r"));
+        assertEquals(Optional.of(Month.MARCH), Month.parse("Mae"));
+        assertEquals(Optional.of(Month.APRIL), Month.parse("Apr"));
+        assertEquals(Optional.of(Month.MAY), Month.parse("Mai"));
+        assertEquals(Optional.of(Month.JUNE), Month.parse("Jun"));
+        assertEquals(Optional.of(Month.JULY), Month.parse("Jul"));
+        assertEquals(Optional.of(Month.AUGUST), Month.parse("Aug"));
+        assertEquals(Optional.of(Month.SEPTEMBER), Month.parse("Sep"));
+        assertEquals(Optional.of(Month.OCTOBER), Month.parse("Okt"));
+        assertEquals(Optional.of(Month.NOVEMBER), Month.parse("Nov"));
+        assertEquals(Optional.of(Month.DECEMBER), Month.parse("Dez"));
+    }
+
+    @Test
+    public void parseCorrectlyByFullNameGerman() {
+        assertEquals(Optional.of(Month.JANUARY), Month.parse("Januar"));
+        assertEquals(Optional.of(Month.FEBRUARY), Month.parse("Februar"));
+        assertEquals(Optional.of(Month.MARCH), Month.parse("M�rz"));
+        assertEquals(Optional.of(Month.MARCH), Month.parse("Maerz"));
+        assertEquals(Optional.of(Month.APRIL), Month.parse("April"));
+        assertEquals(Optional.of(Month.MAY), Month.parse("Mai"));
+        assertEquals(Optional.of(Month.JUNE), Month.parse("Juni"));
+        assertEquals(Optional.of(Month.JULY), Month.parse("Juli"));
+        assertEquals(Optional.of(Month.AUGUST), Month.parse("August"));
+        assertEquals(Optional.of(Month.SEPTEMBER), Month.parse("September"));
+        assertEquals(Optional.of(Month.OCTOBER), Month.parse("Oktober"));
+        assertEquals(Optional.of(Month.NOVEMBER), Month.parse("November"));
+        assertEquals(Optional.of(Month.DECEMBER), Month.parse("Dezember"));
+    }
 }