Export no empty lines in RIS format (#3661)

* Do no longer export empty lines in RIS format

* Fix typos

* Extract and explain regex

* Turn regex static final

CHANGELOG.md

@@ -20,6 +20,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - We improved the export of the `address` and `location` field to the MS-Office XML fields. If the address field does not contain a comma, it is treated as single value and exported to the field `city`. [#1750, comment](https://github.com/JabRef/jabref/issues/1750#issuecomment-357539167) 
 For more details refer to the [field mapping help page](http://help.jabref.org/en/MsOfficeBibFieldMapping)
 - We added Facebook and Twitter icons in the toolbar to link to our [Facebook](https://www.facebook.com/JabRef/) and [Twitter](https://twitter.com/jabref_org) pages.
+- We no longer print empty lines when exporting an entry in RIS format [#3634](https://github.com/JabRef/jabref/issues/3634)
 
 ### Fixed
 - We fixed the missing dot in the name of an exported file. [#3576](https://github.com/JabRef/jabref/issues/3576)

src/main/java/org/jabref/logic/exporter/ExporterFactory.java

@@ -47,7 +47,7 @@ public static ExporterFactory create(Map<String, TemplateExporter> customFormats
         exporters.add(new TemplateExporter("iso690txt", "iso690", "iso690txt", FileType.ISO_690_TXT, layoutPreferences, savePreferences));
         exporters.add(new TemplateExporter("endnote", "EndNote", "endnote", FileType.ENDNOTE_TXT, layoutPreferences, savePreferences));
         exporters.add(new TemplateExporter("oocsv", "openoffice-csv", "openoffice", FileType.OO_LO, layoutPreferences, savePreferences));
-        exporters.add(new TemplateExporter("ris", "ris", "ris", FileType.RIS, layoutPreferences, savePreferences).withEncoding(StandardCharsets.UTF_8));
+        exporters.add(new TemplateExporter("ris", "ris", "ris", FileType.RIS, layoutPreferences, savePreferences, true).withEncoding(StandardCharsets.UTF_8));
         exporters.add(new TemplateExporter("misq", "misq", "misq", FileType.MIS_QUARTERLY, layoutPreferences, savePreferences));
         exporters.add(new BibTeXMLExporter());
         exporters.add(new OpenOfficeDocumentCreator());

src/main/java/org/jabref/logic/exporter/TemplateExporter.java

@@ -14,6 +14,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.regex.Pattern;
 
 import org.jabref.JabRefMain;
 import org.jabref.logic.layout.Layout;
@@ -33,13 +34,23 @@ public class TemplateExporter extends Exporter {
 
     private static final String LAYOUT_PREFIX = "/resource/layout/";
 
+    /**
+     * A regular expression that matches blank lines
+     *
+     * ?m activates "multimode", which makes ^ match line starts/ends.
+     * \\s simply marks any whitespace character
+     */
+    private static final Pattern BLANK_LINE_MATCHER = Pattern.compile("(?m)^\\s");
+
     private static final Logger LOGGER = LoggerFactory.getLogger(TemplateExporter.class);
+
     private final String lfFileName;
     private final String directory;
     private final LayoutFormatterPreferences layoutPreferences;
     private final SavePreferences savePreferences;
     private Charset encoding; // If this value is set, it will be used to override the default encoding for the getCurrentBasePanel.
     private boolean customExport;
+    private boolean deleteBlankLines;
 
     /**
      * Initialize another export format based on templates stored in dir with
@@ -93,6 +104,25 @@ public TemplateExporter(String consoleName, String lfFileName, String directory,
         this(extension.getDescription(), consoleName, lfFileName, directory, extension, layoutPreferences, savePreferences);
     }
 
+    /**
+     * Initialize another export format based on templates stored in dir with
+     * layoutFile lfFilename.
+     * The display name is automatically derived from the FileType
+     *
+     *
+     * @param consoleName Name to call this format in the console.
+     * @param lfFileName  Name of the main layout file.
+     * @param directory   Directory in which to find the layout file.
+     * @param extension   Should contain the . (for instance .txt).
+     * @param layoutPreferences Preferences for layout
+     * @param savePreferences Preferences for saving
+     * @param deleteBlankLines If blank lines should be remove (default: false)
+     */
+    public TemplateExporter(String consoleName, String lfFileName, String directory, FileType extension, LayoutFormatterPreferences layoutPreferences, SavePreferences savePreferences, boolean deleteBlankLines) {
+        this(extension.getDescription(), consoleName, lfFileName, directory, extension, layoutPreferences, savePreferences);
+        this.deleteBlankLines = deleteBlankLines;
+    }
+
     /**
      * Indicate whether this is a custom export. A custom export looks for its
      * layout files using a normal file path, while a built-in export looks in
@@ -257,7 +287,12 @@ public void export(final BibDatabaseContext databaseContext, final Path file,
 
                 // Write the entry
                 if (layout != null) {
-                    ps.write(layout.doLayout(entry, databaseContext.getDatabase()));
+                    if (deleteBlankLines) {
+                        String withoutBlankLines = BLANK_LINE_MATCHER.matcher(layout.doLayout(entry, databaseContext.getDatabase())).replaceAll("");
+                        ps.write(withoutBlankLines);
+                    } else {
+                        ps.write(layout.doLayout(entry, databaseContext.getDatabase()));
+                    }
                 }
             }
 

src/main/java/org/jabref/logic/layout/Layout.java

@@ -90,23 +90,21 @@ public void setPostFormatter(LayoutFormatter formatter) {
      * recursive string references are resolved.
      */
     public String doLayout(BibEntry bibtex, BibDatabase database) {
-        StringBuilder sb = new StringBuilder(100);
+        StringBuilder builder = new StringBuilder(100);
 
         for (LayoutEntry layoutEntry : layoutEntries) {
             String fieldText = layoutEntry.doLayout(bibtex, database);
 
-            // 2005.05.05 M. Alver
             // The following change means we treat null fields as "". This is to fix the
-            // problem of whitespace disappearing after missing fields. Hoping there are
-            // no side effects.
+            // problem of whitespace disappearing after missing fields.
             if (fieldText == null) {
                 fieldText = "";
             }
 
-            sb.append(fieldText);
+            builder.append(fieldText);
         }
 
-        return sb.toString();
+        return builder.toString();
     }
 
     /**