Fixed serialisation of cropId and startDate

src/main/java/ch/zhaw/gartenverwaltung/io/JsonGardenPlan.java

@@ -2,8 +2,10 @@ package ch.zhaw.gartenverwaltung.io;
 
 import ch.zhaw.gartenverwaltung.types.Crop;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 import com.fasterxml.jackson.datatype.jsr310.deser.LocalDateDeserializer;
+import com.fasterxml.jackson.datatype.jsr310.ser.LocalDateSerializer;
 
 import java.io.File;
 import java.io.IOException;
@@ -29,9 +31,12 @@ public class JsonGardenPlan implements GardenPlan {
     private final static JavaTimeModule timeModule = new JavaTimeModule();
     private final static String INVALID_DATASOURCE_MSG = "Invalid datasource specified!";
     static {
-        DateTimeFormatter dateFormat = DateTimeFormatter.ofPattern("yy-MM-dd");
+        DateTimeFormatter dateFormat = DateTimeFormatter.ofPattern("yyyy-MM-dd");
         LocalDateDeserializer dateDeserializer = new LocalDateDeserializer(dateFormat);
+        LocalDateSerializer dateSerializer = new LocalDateSerializer(dateFormat);
+
         timeModule.addDeserializer(LocalDate.class, dateDeserializer);
+        timeModule.addSerializer(LocalDate.class, dateSerializer);
     }
 
     /**
@@ -123,6 +128,7 @@ public class JsonGardenPlan implements GardenPlan {
             try {
                 new ObjectMapper()
                         .registerModule(timeModule)
+                        .registerModule(new Jdk8Module())
                         .writeValue(new File(dataSource.toURI()), cropMap.values());
             } catch (URISyntaxException e) {
                 // TODO: Log