Added layout DateFormatter, see #1249 (#1584)

* Added layout DateFormatter, see #1249

* Removed comment (sorry about that)

CHANGELOG.md

@@ -13,6 +13,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 
 ### Changed
 - [#1026](https://github.com/JabRef/jabref/issues/1026) JabRef does no longer delete user comments outside of BibTeX entries and strings
+- [#1249](https://github.com/JabRef/jabref/issues/1249) Date layout formatter added
 
 ### Fixed
 - Fixed [#1264](https://github.com/JabRef/jabref/issues/1264): S with caron does not render correctly

src/main/java/net/sf/jabref/logic/layout/format/DateFormatter.java

@@ -0,0 +1,26 @@
+package net.sf.jabref.logic.layout.format;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+
+import net.sf.jabref.logic.layout.ParamLayoutFormatter;
+
+
+public class DateFormatter implements ParamLayoutFormatter {
+
+    private String formatString = "yyyy-MM-dd"; // Use ISO-format as default
+
+
+    @Override
+    public String format(String fieldText) {
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(formatString);
+        LocalDate date = LocalDate.parse(fieldText, DateTimeFormatter.ISO_LOCAL_DATE);
+        return date.format(formatter);
+    }
+
+    @Override
+    public void setArgument(String arg) {
+        formatString = arg;
+    }
+
+}

src/test/java/net/sf/jabref/logic/layout/format/DateFormatterTest.java

@@ -0,0 +1,29 @@
+package net.sf.jabref.logic.layout.format;
+
+import net.sf.jabref.logic.layout.ParamLayoutFormatter;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+public class DateFormatterTest {
+
+    private ParamLayoutFormatter formatter;
+
+    @Before
+    public void setUp() {
+        formatter = new DateFormatter();
+    }
+
+    @Test
+    public void testDefaultFormat() {
+        Assert.assertEquals("2016-07-15", formatter.format("2016-07-15"));
+    }
+
+    @Test
+    public void testRequestedFormat() {
+        formatter.setArgument("MM/yyyy");
+        Assert.assertEquals("07/2016", formatter.format("2016-07-15"));
+    }
+
+}