Fix DublinCoreExtractor (and add more tests)

src/main/java/org/jabref/logic/xmp/DublinCoreExtractor.java

@@ -85,9 +85,10 @@ private void extractYearAndMonth() {
             }
             if (calender != null) {
                 bibEntry.setField(StandardField.YEAR, String.valueOf(calender.get(Calendar.YEAR)));
+                int monthNumber = calender.get(Calendar.MONTH) + 1;
                 // not the 1st of January
-                if (!((calender.get(Calendar.MONTH) == 0) && (calender.get(Calendar.DAY_OF_MONTH) == 1))) {
-                    Month.getMonthByNumber(calender.get(Calendar.MONTH) + 1)
+                if (!((monthNumber == 1) && (calender.get(Calendar.DAY_OF_MONTH) == 1))) {
+                    Month.getMonthByNumber(monthNumber)
                          .ifPresent(month -> bibEntry.setMonth(month));
                 }
             }
@@ -125,16 +126,13 @@ private void extractPublisher() {
     }
 
     /**
-     * This method sets all fields, which are custom in bibtext and therefore supported by jabref, but which are not
+     * This method sets all fields, which are custom in BibTeX and therefore supported by JabRef, but which are not
      * included in the DublinCore format.
-     * <p/>
+     * <p>
      * The relation attribute of DublinCore is abused to insert these custom fields.
      */
     private void extractBibTexFields() {
-        List<String> relationships = dcSchema.getRelations();
-
         Predicate<String> isBibTeXElement = s -> s.startsWith("bibtex/");
-
         Consumer<String> splitBibTeXElement = s -> {
             // the default pattern is bibtex/key/value, but some fields contains url etc.
             // so the value property contains additional slashes, which makes the usage of
@@ -151,10 +149,11 @@ private void extractBibTexFields() {
                 // see also DublinCoreExtractor#extractYearAndMonth
                 if (StandardField.MONTH.equals(key)) {
                     Optional<Month> parsedMonth = Month.parse(value);
-                    parsedMonth.ifPresent(month -> bibEntry.setField(key, month.getShortName()));
+                    parsedMonth.ifPresent(bibEntry::setMonth);
                 }
             }
         };
+        List<String> relationships = dcSchema.getRelations();
         if (relationships != null) {
             relationships.stream()
                          .filter(isBibTeXElement)
@@ -221,19 +220,22 @@ private void extractType() {
      * To understand how to get hold of a DublinCore have a look in the test cases for XMPUtil.
      * <p>
      * The BibEntry is build by mapping individual fields in the dublin core (like creator, title, subject) to fields in
-     * a bibtex bibEntry.
+     * a bibtex bibEntry. In case special "bibtex/" entries are contained, the normal dublin core fields take
+     * precedence. For instance, the dublin core date takes precedence over bibtex/month.
      *
-     * @return The bibtex bibEntry found in the document information.
+     * @return The bibEntry extracted from the document information.
      */
     public Optional<BibEntry> extractBibtexEntry() {
+        // first extract "bibtex/" entries
+        this.extractBibTexFields();
 
+        // then extract all "standard" dublin core entries
         this.extractEditor();
         this.extractAuthor();
         this.extractYearAndMonth();
         this.extractAbstract();
         this.extractDOI();
         this.extractPublisher();
-        this.extractBibTexFields();
         this.extractRights();
         this.extractSource();
         this.extractSubject();

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

@@ -17,10 +17,13 @@ private CanonicalBibtexEntry() {
     }
 
     /**
-     * This returns a canonical BibTeX serialization. Special characters such as "{" or "&" are NOT escaped, but written
-     * as is
+     * This returns a canonical BibTeX serialization. Serializes all fields, even the JabRef internal ones. Does NOT
+     * serialize "KEY_FIELD" as field, but as key
      *
-     * Serializes all fields, even the JabRef internal ones. Does NOT serialize "KEY_FIELD" as field, but as key
+     * <ul>
+     *     <li>Special characters such as "{" or "&" are NOT escaped, but written as</li>
+     *     <li>String constants are not handled. That means, <code>month = apr</code> in a bib file gets <code>month = {#apr#}</code>. This indicates that the month field is correctly stored</li>
+     * </ul>
      */
     public static String getCanonicalRepresentation(BibEntry entry) {
         StringBuilder sb = new StringBuilder();
@@ -50,7 +53,7 @@ public static String getCanonicalRepresentation(BibEntry entry) {
         // generate field entries
         StringJoiner sj = new StringJoiner(",\n", "", "\n");
         for (String fieldName : sortedFields) {
-            String line = String.format("  %s = {%s}", fieldName, String.valueOf(mapFieldToValue.get(fieldName)).replaceAll("\\r\\n","\n"));
+            String line = String.format("  %s = {%s}", fieldName, String.valueOf(mapFieldToValue.get(fieldName)).replaceAll("\\r\\n", "\n"));
             sj.add(line);
         }
         sb.append(sj);
@@ -59,5 +62,4 @@ public static String getCanonicalRepresentation(BibEntry entry) {
         sb.append('}');
         return sb.toString();
     }
-
 }

src/test/java/org/jabref/logic/importer/fileformat/BibtexParserTest.java

@@ -1784,4 +1784,13 @@ void bibTeXConstantAprilIsDisplayedAsConstant() throws ParseException {
 
         assertEquals("#apr#", result.get().getField(StandardField.MONTH).get());
     }
+
+    @Test
+    void bibTeXConstantAprilIsParsedAsStringMonthAprilWhenReadingTheField() throws ParseException {
+        Optional<BibEntry> result = parser.parseSingleEntry("@Misc{m, month = apr }" );
+
+        assertEquals(Optional.of("#apr#"), result.get().getField(StandardField.MONTH));
+    }
+
+
 }

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

@@ -0,0 +1,17 @@
+package org.jabref.model.entry;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CanonicalBibtexEntryTest {
+
+    @Test
+    void canonicalRepresentationIsCorrectForStringMonth() {
+        BibEntry entry = new BibEntry();
+        entry.setMonth(Month.MAY);
+        assertEquals("@misc{,\n" +
+                "  month = {#may#}\n" +
+                "}", CanonicalBibtexEntry.getCanonicalRepresentation(entry));
+    }
+}