Add field published_on and title to Issue

/refs #16

Add field published_on and title to Issue and display both fields.

kontor-spring/src/main/java/de/thpeetz/kontor/comics/views/IssueForm.java

@@ -1,5 +1,7 @@
 package de.thpeetz.kontor.comics.views;
 
+import java.time.*;
+import java.time.format.*;
 import java.util.List;
 
 import com.vaadin.flow.component.ComponentEvent;
@@ -9,6 +11,7 @@ import com.vaadin.flow.component.button.Button;
 import com.vaadin.flow.component.button.ButtonVariant;
 import com.vaadin.flow.component.checkbox.Checkbox;
 import com.vaadin.flow.component.combobox.ComboBox;
+import com.vaadin.flow.component.datepicker.*;
 import com.vaadin.flow.component.formlayout.FormLayout;
 import com.vaadin.flow.component.grid.*;
 import com.vaadin.flow.component.orderedlayout.HorizontalLayout;
@@ -43,6 +46,23 @@ public class IssueForm extends FormLayout {
 
     public IssueForm(List<Comic> comics, List<Volume> volumes) {
         addClassName("issue-form");
+        binder.forField(publishedOn).withConverter(new Converter<String, YearMonth>() {
+            @Override
+            public Result<YearMonth> convertToModel(String value, ValueContext context) {
+                try {
+                    YearMonth result = YearMonth.parse(value);
+                    return Result.ok(result);
+                } catch (DateTimeParseException e) {
+                    return Result.error("invalid year-month format");
+                }
+            }
+
+            @Override
+            public String convertToPresentation(YearMonth value, ValueContext context) {
+                if (value == null) return "";
+                return value.format(DateTimeFormatter.ofPattern("yyyy-MM"));
+            }
+        }).bind(Issue::getPublishedOn, Issue::setPublishedOn);
         binder.bindInstanceFields(this);
 
         comic.setItems(comics);