Add support for java.util.Calendar as epoch millis or string format with timezone (#342)

* Add support for java.util.Calendar as epoch millis or string format with timezone

* Fix format

Author: rbygrave

blackbox-test/src/main/java/org/example/customer/datetime/MyCalData.java

@@ -0,0 +1,9 @@
+package org.example.customer.datetime;
+
+import io.avaje.jsonb.Json;
+
+import java.util.Calendar;
+
+@Json
+public record MyCalData(Calendar cal) {
+}

blackbox-test/src/test/java/org/example/customer/datetime/CalendarTest.java

@@ -0,0 +1,51 @@
+package org.example.customer.datetime;
+
+import io.avaje.jsonb.JsonType;
+import io.avaje.jsonb.Jsonb;
+import org.junit.jupiter.api.Test;
+
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.util.GregorianCalendar;
+import java.util.TimeZone;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class CalendarTest {
+
+  @Test
+  void calendarAsEpochMillis() {
+    Jsonb jsonb = Jsonb.builder().calendarAsString(false).build();
+    JsonType<MyCalData> type = jsonb.type(MyCalData.class);
+
+    var zdt = ZonedDateTime.of(2001, 3, 23, 0, 1, 2, 0, ZoneId.of("Pacific/Auckland"));
+    var calendar = GregorianCalendar.from(zdt);
+    var data = new MyCalData(calendar);
+    var asJson = type.toJson(data);
+    var fromJson = type.fromJson(asJson);
+
+    assertThat(fromJson.cal().toInstant()).isEqualTo(data.cal().toInstant());
+    // deserialized as UTC
+    assertThat(fromJson.cal().getTimeZone()).isEqualTo(TimeZone.getTimeZone(ZoneId.of("UTC")));
+  }
+
+  @Test
+  void calendarAsString() {
+    Jsonb jsonb = Jsonb.builder().calendarAsString(true).build();
+    JsonType<MyCalData> type = jsonb.type(MyCalData.class);
+
+    var zdt = ZonedDateTime.of(2001, 3, 23, 0, 1, 2, 0, ZoneId.of("Pacific/Auckland"));
+    // note calendar deserialized using ISO8601 with
+    // setFirstDayOfWeek(MONDAY) and setMinimalDaysInFirstWeek(4);
+    var calendar = GregorianCalendar.from(zdt);
+    var data = new MyCalData(calendar);
+    var asJson = type.toJson(data);
+    var fromJson = type.fromJson(asJson);
+
+    assertThat(fromJson.cal().toInstant()).isEqualTo(data.cal().toInstant());
+    assertThat(fromJson.cal().getTimeZone()).isEqualTo(data.cal().getTimeZone());
+    assertThat(fromJson.cal().getFirstDayOfWeek()).isEqualTo(data.cal().getFirstDayOfWeek());
+    assertThat(fromJson.cal().getMinimalDaysInFirstWeek()).isEqualTo(data.cal().getMinimalDaysInFirstWeek());
+    assertThat(fromJson).isEqualTo(data);
+  }
+}

jsonb/src/main/java/io/avaje/jsonb/Jsonb.java

@@ -386,6 +386,12 @@ interface Builder {
      */
     Builder mathTypesAsString(boolean mathTypesAsString);
 
+    /**
+     * Set to true for Calendar to serialise as String with timezone and false to serialise
+     * as UTC epoch millis. Defaults to false.
+     */
+    Builder calendarAsString(boolean calendarAsString);
+
     /**
      * Determines how byte buffers are recycled
      */

jsonb/src/main/java/io/avaje/jsonb/core/CoreAdapterBuilder.java

@@ -36,13 +36,14 @@ final class CoreAdapterBuilder {
   private final Map<Object, JsonAdapter<?>> adapterCache = new ConcurrentHashMap<>();
   private final ReentrantLock lock = new ReentrantLock();
 
-  CoreAdapterBuilder(DJsonb context, List<AdapterFactory> userFactories, boolean mathAsString) {
+  CoreAdapterBuilder(DJsonb context, List<AdapterFactory> userFactories, boolean mathAsString, boolean calendarAsString) {
     this.context = context;
     this.factories = new ArrayList<>();
     this.factories.addAll(userFactories);
     this.factories.add(CoreAdapters.FACTORY);
     this.factories.add(BasicTypeAdapters.FACTORY);
     this.factories.add(JavaTimeAdapters.FACTORY);
+    this.factories.add(new JavaTimeAdapters.CalendarFactory(calendarAsString));
     this.factories.add(new MathAdapters(mathAsString));
     this.factories.add(CoreAdapters.COLLECTION_FACTORY);
     this.factories.add(CoreAdapters.MAP_FACTORY);

jsonb/src/main/java/io/avaje/jsonb/core/DJsonb.java

@@ -39,9 +39,10 @@ final class DJsonb implements Jsonb {
       boolean serializeEmpty,
       boolean failOnUnknown,
       boolean mathAsString,
+      boolean calendarAsString,
       BufferRecycleStrategy strategy) {
 
-    this.builder = new CoreAdapterBuilder(this, factories, mathAsString);
+    this.builder = new CoreAdapterBuilder(this, factories, mathAsString, calendarAsString);
     if (adapter != null) {
       this.io = adapter;
     } else {
@@ -245,6 +246,7 @@ static final class DBuilder implements Jsonb.Builder {
     private final List<AdapterFactory> factories = new ArrayList<>();
     private boolean failOnUnknown;
     private boolean mathTypesAsString;
+    private boolean calendarAsString;
     private boolean serializeNulls;
     private boolean serializeEmpty = true;
     private JsonStream adapter;
@@ -274,6 +276,12 @@ public Builder mathTypesAsString(boolean mathTypesAsString) {
       return this;
     }
 
+    @Override
+    public Builder calendarAsString(boolean calendarAsString) {
+      this.calendarAsString = calendarAsString;
+      return this;
+    }
+
     @Override
     public Builder bufferRecycling(BufferRecycleStrategy strategy) {
       this.strategy = strategy;
@@ -326,7 +334,7 @@ private void registerComponents() {
     @Override
     public DJsonb build() {
       registerComponents();
-      return new DJsonb(adapter, factories, serializeNulls, serializeEmpty, failOnUnknown, mathTypesAsString, strategy);
+      return new DJsonb(adapter, factories, serializeNulls, serializeEmpty, failOnUnknown, mathTypesAsString, calendarAsString, strategy);
     }
 
     static <T> AdapterFactory newAdapterFactory(Type type, JsonAdapter<T> jsonAdapter) {

jsonb/src/main/java/io/avaje/jsonb/core/JavaTimeAdapters.java

@@ -1,13 +1,18 @@
 package io.avaje.jsonb.core;
 
+import java.lang.reflect.Type;
+import java.util.Calendar;
 import java.util.Date;
 
 import io.avaje.json.JsonAdapter;
 import io.avaje.jsonb.AdapterFactory;
 import io.avaje.json.JsonReader;
 import io.avaje.json.JsonWriter;
+import io.avaje.jsonb.Jsonb;
 
 import java.time.*;
+import java.util.GregorianCalendar;
+import java.util.TimeZone;
 
 /**
  * Adds support for java time types.
@@ -34,26 +39,44 @@ final class JavaTimeAdapters {
     return null;
   };
 
+  static final class CalendarFactory implements AdapterFactory {
+
+    private final boolean calendarAsString;
+
+    CalendarFactory(boolean calendarAsString) {
+      this.calendarAsString = calendarAsString;
+    }
+
+    @Override
+    public JsonAdapter<?> create(Type type, Jsonb jsonb) {
+      if (type == Calendar.class) {
+        return calendarAsString
+          ? JavaTimeAdapters.CALENDAR_ZONED.nullSafe()
+          : JavaTimeAdapters.CALENDAR_EPOCH_MILLIS.nullSafe() ;
+      }
+      return null;
+    }
+  }
+
   /**
    * Using ISO-8601
    */
-
   private static final JsonAdapter<Date> UTIL_DATE = new JsonAdapter<>() {
-      @Override
-      public Date fromJson(JsonReader reader) {
-        return Date.from(Instant.parse(reader.readString()));
-      }
+    @Override
+    public Date fromJson(JsonReader reader) {
+      return Date.from(Instant.parse(reader.readString()));
+    }
 
-      @Override
-      public void toJson(JsonWriter writer, Date value) {
-        writer.value(value.toInstant().toString());
-      }
+    @Override
+    public void toJson(JsonWriter writer, Date value) {
+      writer.value(value.toInstant().toString());
+    }
 
-      @Override
-      public String toString() {
-        return "JsonAdapter(Date)";
-      }
-    };
+    @Override
+    public String toString() {
+      return "JsonAdapter(Date)";
+    }
+  };
 
   private static final JsonAdapter<Duration> DURATION_ADAPTER = new JsonAdapter<>() {
     @Override
@@ -140,6 +163,49 @@ public String toString() {
     }
   };
 
+  private static final JsonAdapter<Calendar> CALENDAR_ZONED = new JsonAdapter<>() {
+    @Override
+    public Calendar fromJson(JsonReader reader) {
+      final ZonedDateTime zdt = ZonedDateTime.parse(reader.readString());
+      return GregorianCalendar.from(zdt);
+    }
+
+    @Override
+    public void toJson(JsonWriter writer, Calendar value) {
+      TimeZone timeZone = value.getTimeZone();
+      ZonedDateTime zonedDateTime = ZonedDateTime.ofInstant(value.toInstant(), timeZone.toZoneId());
+      writer.value(zonedDateTime.toString());
+    }
+
+    @Override
+    public String toString() {
+      return "JsonAdapter(Calendar)";
+    }
+  };
+
+  private static final JsonAdapter<Calendar> CALENDAR_EPOCH_MILLIS = new JsonAdapter<>() {
+    private final TimeZone UTC = TimeZone.getTimeZone(ZoneId.of("UTC"));
+
+    @Override
+    public Calendar fromJson(JsonReader reader) {
+      long epochMillis = reader.readLong();
+      Calendar instance = Calendar.getInstance();
+      instance.setTimeInMillis(epochMillis);
+      instance.setTimeZone(UTC);
+      return instance;
+    }
+
+    @Override
+    public void toJson(JsonWriter writer, Calendar value) {
+      writer.value(value.getTimeInMillis());
+    }
+
+    @Override
+    public String toString() {
+      return "JsonAdapter(Calendar)";
+    }
+  };
+
   private static final JsonAdapter<ZoneOffset> ZONE_OFFSET_ADAPTER = new JsonAdapter<>() {
     @Override
     public ZoneOffset fromJson(JsonReader reader) {
@@ -170,7 +236,7 @@ public void toJson(JsonWriter writer, ZoneId value) {
 
     @Override
     public String toString() {
-      return "JsonAdapter(ZoneOffset)";
+      return "JsonAdapter(ZoneId)";
     }
   };