Added Enum support for POJOs

JAVA-268

Author: rozza

bson/src/main/org/bson/codecs/pojo/EnumCodec.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2017 MongoDB, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.bson.codecs.pojo;
+
+import org.bson.BsonReader;
+import org.bson.BsonWriter;
+import org.bson.codecs.Codec;
+import org.bson.codecs.DecoderContext;
+import org.bson.codecs.EncoderContext;
+
+final class EnumCodec<T extends Enum<T>> implements Codec<T> {
+    private final Class<T> clazz;
+
+    EnumCodec(final Class<T> clazz) {
+        this.clazz = clazz;
+    }
+
+    @Override
+    public void encode(final BsonWriter writer, final T value, final EncoderContext encoderContext) {
+        writer.writeString(value.name());
+    }
+
+    @Override
+    public Class<T> getEncoderClass() {
+        return clazz;
+    }
+
+    @Override
+    public T decode(final BsonReader reader, final DecoderContext decoderContext) {
+        return Enum.valueOf(clazz, reader.readString());
+    }
+}

bson/src/main/org/bson/codecs/pojo/PojoCodec.java

@@ -194,9 +194,17 @@ private  <S> Codec<S> getCodecFromTypeData(final TypeData<S> typeData) {
             codec = new CollectionCodec(head, getCodecFromTypeData(typeData.getTypeParameters().get(0)));
         } else if (Map.class.isAssignableFrom(head)) {
             codec = new MapCodec(head, getCodecFromTypeData(typeData.getTypeParameters().get(1)));
+        } else if (Enum.class.isAssignableFrom(head)) {
+            try {
+                codec = registry.get(head);
+            } catch (CodecConfigurationException e) {
+                codec = new EnumCodec((Class<Enum<?>>) head);
+            }
         } else {
             codec = getCodecFromClass(head);
         }
+
+
         return codec;
     }
 

bson/src/test/unit/org/bson/codecs/pojo/PojoCodecTest.java

@@ -50,6 +50,8 @@
 import org.bson.codecs.pojo.entities.ShapeModelAbstract;
 import org.bson.codecs.pojo.entities.ShapeModelCircle;
 import org.bson.codecs.pojo.entities.ShapeModelRectangle;
+import org.bson.codecs.pojo.entities.SimpleEnum;
+import org.bson.codecs.pojo.entities.SimpleEnumModel;
 import org.bson.codecs.pojo.entities.SimpleGenericsModel;
 import org.bson.codecs.pojo.entities.SimpleModel;
 import org.bson.codecs.pojo.entities.SimpleNestedPojoModel;
@@ -66,7 +68,9 @@
 import static java.lang.String.format;
 import static java.util.Arrays.asList;
 import static java.util.Collections.singletonList;
+import static org.bson.codecs.configuration.CodecRegistries.fromCodecs;
 import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
+import static org.bson.codecs.configuration.CodecRegistries.fromRegistries;
 import static org.bson.codecs.pojo.Conventions.NO_CONVENTIONS;
 
 public final class PojoCodecTest extends PojoTestCase {
@@ -340,6 +344,20 @@ public void apply(final ClassModelBuilder<?> classModelBuilder) {
                         + "           'simple_model': {'integer_field': 42, 'string_field': 'myString' } } }");
     }
 
+    @Test
+    public void testEnumSupport() {
+        SimpleEnumModel model = new SimpleEnumModel(SimpleEnum.BRAVO);
+        roundTrip(getPojoCodecProviderBuilder(SimpleEnumModel.class), model, "{ 'myEnum': 'BRAVO' }");
+    }
+
+    @Test
+    public void testEnumSupportWithCustomCodec() {
+        SimpleEnumModel model = new SimpleEnumModel(SimpleEnum.BRAVO);
+        CodecRegistry registry = fromRegistries(getCodecRegistry(getPojoCodecProviderBuilder(SimpleEnumModel.class)),
+                fromCodecs(new SimpleEnumCodec()));
+        roundTrip(registry, model, "{ 'myEnum': 1 }");
+    }
+
     @Test
     @SuppressWarnings("unchecked")
     public void testCustomCodec() {

bson/src/test/unit/org/bson/codecs/pojo/PojoTestCase.java

@@ -40,6 +40,7 @@
 import org.bson.codecs.pojo.entities.ReusedGenericsModel;
 import org.bson.codecs.pojo.entities.ShapeModelCircle;
 import org.bson.codecs.pojo.entities.ShapeModelRectangle;
+import org.bson.codecs.pojo.entities.SimpleEnum;
 import org.bson.codecs.pojo.entities.SimpleGenericsModel;
 import org.bson.codecs.pojo.entities.SimpleModel;
 import org.bson.codecs.pojo.entities.SimpleNestedPojoModel;
@@ -297,4 +298,30 @@ public String decode(final BsonReader reader, final DecoderContext decoderContex
             return reader.readObjectId().toHexString();
         }
     }
+
+    class SimpleEnumCodec implements Codec<SimpleEnum> {
+
+        @Override
+        public void encode(final BsonWriter writer, final SimpleEnum value, final EncoderContext encoderContext) {
+            writer.writeInt32(value.ordinal());
+        }
+
+        @Override
+        public Class<SimpleEnum> getEncoderClass() {
+            return SimpleEnum.class;
+        }
+
+        @Override
+        public SimpleEnum decode(final BsonReader reader, final DecoderContext decoderContext) {
+            int ordinal = reader.readInt32();
+            switch (ordinal){
+                case 0:
+                    return SimpleEnum.ALPHA;
+                case 1:
+                    return SimpleEnum.BRAVO;
+                default:
+                    return SimpleEnum.CHARLIE;
+            }
+        }
+    }
 }

bson/src/test/unit/org/bson/codecs/pojo/entities/SimpleEnum.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2017 MongoDB, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.bson.codecs.pojo.entities;
+
+public enum SimpleEnum {
+    ALPHA,
+    BRAVO,
+    CHARLIE
+}

bson/src/test/unit/org/bson/codecs/pojo/entities/SimpleEnumModel.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2017 MongoDB, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.bson.codecs.pojo.entities;
+
+public final class SimpleEnumModel {
+
+    private SimpleEnum myEnum;
+
+    public SimpleEnumModel() {
+    }
+
+    public SimpleEnumModel(final SimpleEnum myEnum) {
+        this.myEnum = myEnum;
+    }
+
+    /**
+     * Returns the myEnum
+     *
+     * @return the myEnum
+     */
+    public SimpleEnum getMyEnum() {
+        return myEnum;
+    }
+
+    /**
+     * Sets the myEnum
+     *
+     * @param myEnum the myEnum
+     * @return this
+     */
+    public SimpleEnumModel myEnum(final SimpleEnum myEnum) {
+        this.myEnum = myEnum;
+        return this;
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        SimpleEnumModel that = (SimpleEnumModel) o;
+
+        if (getMyEnum() != that.getMyEnum()) {
+            return false;
+        }
+
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        return getMyEnum() != null ? getMyEnum().hashCode() : 0;
+    }
+}

docs/reference/content/bson/pojos.md

@@ -149,6 +149,40 @@ serializable because they are bound to the concrete types `Integer`, `String` an
 On their own, instances of `GenericTree` or `GenericClass` are not serializable by the `PojoCodec`. This is because the runtime type parameter
 information is erased by the JVM, and the type parameters cannot be specialized accurately.
 
+### Enum support
+
+Enums are fully supported. The `PojoCodec` uses the name of the enum constant as the field value. This is then converted back into an Enum 
+value by the codec using the static `Enum.valueOf` method.
+
+Take the following example:
+
+```Java
+
+public enum Membership {
+    UNREGISTERED,
+    SUBSCRIBER,
+    PREMIUM
+}
+
+public class Person {
+    private String firstName;
+    private String lastName;
+    private Member membership = Member.UNREGISTERED;
+
+    public Person() { }
+
+    public Person(final String firstName, final String lastName, final Membership membership) { }
+
+    // Rest of implementation
+}
+```
+
+The instance of `new Person("Bryan", "May", SUBSCRIBER);` would be serialized to the equivalent of 
+`{ firstName: "Bryan", lastName: "May", membership: "SUBSCRIBER"}`. 
+
+If you require an alternative representation of the Enum, you can override how a Enum is stored by registering a custom `Codec` for the Enum in the `CodecRegistry`.
+
+
 ### Conventions
 
 The [`Convention`]({{<apiref "org/bson/codecs/pojo/Convention.html">}}) interface provides a mechanism for `ClassModelBuilder`