Add jackson behavior for fields

Added classes to make gson treat fields as jackson does.
Added check for input OR output fields.
Corrected comment about annotation names.
Removed trailing spaces.
Extracted some string constants.
Fixed checkstyle issue.

Change-Id: I665b31774086d72a5a95bee6cf3486a019b72402
Issue-ID: POLICY-1428
Signed-off-by: Jim Hahn <jrh3@att.com>

3 files changed, 333 insertions, 0 deletions

diff --git a/gson/src/main/java/org/onap/policy/common/gson/JacksonFieldAdapterFactory.java b/gson/src/main/java/org/onap/policy/common/gson/JacksonFieldAdapterFactory.java
new file mode 100644
index 00000000..67c51449
--- /dev/null
+++ b/gson/src/main/java/org/onap/policy/common/gson/JacksonFieldAdapterFactory.java
@@ -0,0 +1,181 @@
+/*
+ * ============LICENSE_START=======================================================
+ * ONAP
+ * ================================================================================
+ * Copyright (C) 2019 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * 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.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.common.gson;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
+import org.onap.policy.common.gson.internal.ClassWalker;
+import org.onap.policy.common.gson.internal.Deserializer;
+import org.onap.policy.common.gson.internal.FieldDeserializer;
+import org.onap.policy.common.gson.internal.FieldSerializer;
+import org.onap.policy.common.gson.internal.Serializer;
+
+/**
+ * Factory that serializes/deserializes class fields following the normal behavior of
+ * jackson. Supports the following annotations:
+ * <ul>
+ * <li>GsonJsonIgnore</li>
+ * <li>GsonJsonProperty</li>
+ * </ul>
+ *
+ * <p>Note: {@link JacksonExclusionStrategy} must also be registered with the gson object.
+ */
+public class JacksonFieldAdapterFactory implements TypeAdapterFactory {
+
+    @Override
+    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+        Class<? super T> clazz = type.getRawType();
+
+        if (!JacksonExclusionStrategy.isManaged(clazz)) {
+            return null;
+        }
+
+        ClassWalker data = new ClassWalker();
+        data.walkClassHierarchy(clazz);
+
+        if (data.getInProps(Field.class).isEmpty() && data.getOutProps(Field.class).isEmpty()) {
+            // no fields to serialize
+            return null;
+        }
+
+        return new JacksonFieldAdapter<>(gson, data, gson.getDelegateAdapter(this, type));
+    }
+
+    /**
+     * Adapter for a single class.
+     *
+     * @param <T> type of class on which the adapter works
+     */
+    private static class JacksonFieldAdapter<T> extends TypeAdapter<T> {
+
+        /**
+         * Used to create an object of the given class.
+         */
+        private final TypeAdapter<T> delegate;
+
+        /**
+         * Used to serialize/deserialize a JsonElement.
+         */
+        private final TypeAdapter<JsonElement> elementAdapter;
+
+        /**
+         * Serializers for each item within the object.
+         */
+        private final Serializer[] serializers;
+
+        /**
+         * Deserializers for each item within the object.
+         */
+        private final Deserializer[] deserializers;
+
+        /**
+         * Constructs the object.
+         *
+         * @param gson the associated gson object
+         * @param data data used to configure the adapter
+         * @param delegate default constructor for the type
+         */
+        public JacksonFieldAdapter(Gson gson, ClassWalker data, TypeAdapter<T> delegate) {
+            this.delegate = delegate;
+
+            this.elementAdapter = gson.getAdapter(JsonElement.class);
+
+            // create serializers
+            this.serializers = makeSerializers(gson, data).toArray(new Serializer[0]);
+
+            // create deserializers
+            this.deserializers = makeDeserializers(gson, data).toArray(new Deserializer[0]);
+        }
+
+        /**
+         * Creates a complete list of serializers.
+         *
+         * @param gson the associated gson object
+         * @param data data used to configure the serializers
+         * @return a list of all serializers
+         */
+        private List<Serializer> makeSerializers(Gson gson, ClassWalker data) {
+            List<Serializer> ser = new ArrayList<Serializer>();
+
+            data.getOutProps(Field.class).forEach(field -> ser.add(new FieldSerializer(gson, field)));
+
+            return ser;
+        }
+
+        /**
+         * Creates a complete list of deserializers.
+         *
+         * @param gson the associated gson object
+         * @param data data used to configure the deserializers
+         * @return a list of all deserializers
+         */
+        private List<Deserializer> makeDeserializers(Gson gson, ClassWalker data) {
+            List<Deserializer> deser = new ArrayList<Deserializer>();
+
+            data.getInProps(Field.class).forEach(field -> deser.add(new FieldDeserializer(gson, field)));
+
+            return deser;
+        }
+
+        @Override
+        public void write(JsonWriter out, T value) throws IOException {
+            JsonElement tree = delegate.toJsonTree(value);
+
+            if (tree.isJsonObject()) {
+                JsonObject jsonObj = tree.getAsJsonObject();
+
+                // serialize each item from the value into the target tree
+                for (Serializer serializer : serializers) {
+                    serializer.addToTree(value, jsonObj);
+                }
+            }
+
+            elementAdapter.write(out, tree);
+        }
+
+        @Override
+        public T read(JsonReader in) throws IOException {
+            JsonElement tree = elementAdapter.read(in);
+            T object = delegate.fromJsonTree(tree);
+
+            if (tree.isJsonObject()) {
+                JsonObject jsonObj = tree.getAsJsonObject();
+
+                // deserialize each item from the tree into the target object
+                for (Deserializer dser : deserializers) {
+                    dser.getFromTree(jsonObj, object);
+                }
+            }
+
+            return object;
+        }
+    }
+}
diff --git a/gson/src/main/java/org/onap/policy/common/gson/internal/FieldDeserializer.java b/gson/src/main/java/org/onap/policy/common/gson/internal/FieldDeserializer.java
new file mode 100644
index 00000000..14a432d1
--- /dev/null
+++ b/gson/src/main/java/org/onap/policy/common/gson/internal/FieldDeserializer.java
@@ -0,0 +1,72 @@
+/*
+ * ============LICENSE_START=======================================================
+ * ONAP
+ * ================================================================================
+ * Copyright (C) 2019 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * 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.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.common.gson.internal;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import java.lang.reflect.Field;
+
+/**
+ * De-serializer for fields that are exposed.
+ */
+public class FieldDeserializer extends Adapter implements Deserializer {
+
+    public static final String SET_ERR = "cannot set field: ";
+
+    /**
+     * Field within the object.
+     */
+    private final Field field;
+
+    /**
+     * Constructs the object.
+     *
+     * @param gson Gson object providing type adapters
+     * @param field field within the object
+     */
+    public FieldDeserializer(Gson gson, Field field) {
+        super(gson, field);
+
+        this.field = field;
+
+        field.setAccessible(true);
+    }
+
+    @Override
+    public void getFromTree(JsonObject source, Object target) {
+        JsonElement jsonEl = source.get(getPropName());
+        if (jsonEl == null || jsonEl.isJsonNull()) {
+            return;
+        }
+
+        Object value = fromJsonTree(jsonEl);
+
+        try {
+            field.set(target, value);
+
+        } catch (IllegalArgumentException | IllegalAccessException e) {
+            throw new JsonParseException(makeError(SET_ERR), e);
+        }
+    }
+
+}
diff --git a/gson/src/main/java/org/onap/policy/common/gson/internal/FieldSerializer.java b/gson/src/main/java/org/onap/policy/common/gson/internal/FieldSerializer.java
new file mode 100644
index 00000000..1c9d8b37
--- /dev/null
+++ b/gson/src/main/java/org/onap/policy/common/gson/internal/FieldSerializer.java
@@ -0,0 +1,80 @@
+/*
+ * ============LICENSE_START=======================================================
+ * ONAP
+ * ================================================================================
+ * Copyright (C) 2019 AT&T Intellectual Property. All rights reserved.
+ * ================================================================================
+ * 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.
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.common.gson.internal;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonNull;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import java.lang.reflect.Field;
+
+/**
+ * Serializer for fields that are exposed.
+ */
+public class FieldSerializer extends Adapter implements Serializer {
+
+    public static final String GET_ERR = "cannot get field: ";
+
+    /**
+     * Field within the object.
+     */
+    private final Field field;
+
+    /**
+     * Constructs the object.
+     *
+     * @param gson Gson object providing type adapters
+     * @param field field within the object
+     */
+    public FieldSerializer(Gson gson, Field field) {
+        super(gson, field);
+
+        this.field = field;
+
+        field.setAccessible(true);
+    }
+
+    @Override
+    public void addToTree(Object source, JsonObject target) {
+        Object value;
+        try {
+            value = getFromObject(source);
+
+        } catch (IllegalArgumentException | IllegalAccessException e) {
+            throw new JsonParseException(makeError(GET_ERR), e);
+        }
+
+        JsonElement jsonEl = (value == null ? JsonNull.INSTANCE : toJsonTree(value));
+        target.add(getPropName(), jsonEl);
+    }
+
+    /**
+     * Gets the field from the source object. Overridden during junit testing.
+     *
+     * @param source object containing the field
+     * @return the field's value
+     * @throws IllegalAccessException if an error occurs
+     */
+    protected Object getFromObject(Object source) throws IllegalAccessException {
+        return field.get(source);
+    }
+}