Merge "Add jackson behavior for fields"

6 files changed, 752 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);
+    }
+}
diff --git a/gson/src/test/java/org/onap/policy/common/gson/JacksonFieldAdapterFactoryTest.java b/gson/src/test/java/org/onap/policy/common/gson/JacksonFieldAdapterFactoryTest.java
new file mode 100644
index 00000000..9d4b4388
--- /dev/null
+++ b/gson/src/test/java/org/onap/policy/common/gson/JacksonFieldAdapterFactoryTest.java
@@ -0,0 +1,214 @@
+/*
+ * ============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 static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
+import com.google.gson.reflect.TypeToken;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.Test;
+import org.onap.policy.common.gson.JacksonExclusionStrategy;
+import org.onap.policy.common.gson.JacksonFieldAdapterFactory;
+import org.onap.policy.common.gson.annotation.GsonJsonIgnore;
+import org.onap.policy.common.gson.annotation.GsonJsonProperty;
+
+public class JacksonFieldAdapterFactoryTest {
+
+    private static JacksonFieldAdapterFactory factory = new JacksonFieldAdapterFactory();
+
+    private static Gson gson = new GsonBuilder().setExclusionStrategies(new JacksonExclusionStrategy())
+                    .registerTypeAdapterFactory(factory).create();
+
+    @Test
+    public void testCreate() {
+        // unhandled types
+        assertNull(factory.create(gson, TypeToken.get(JsonElement.class)));
+        assertNull(factory.create(gson, TypeToken.get(NothingToSerialize.class)));
+
+        assertNotNull(factory.create(gson, TypeToken.get(Data.class)));
+        assertNotNull(factory.create(gson, TypeToken.get(Derived.class)));
+
+        Data data = new Data();
+
+        // deserialize using fields that aren't in the Data object
+        Data data2 = gson.fromJson("{\"abc\":100}", Data.class);
+        assertEquals(data.toString(), data2.toString());
+
+        // now work with valid fields
+        data.id = 10;
+        data.text = "hello";
+
+        String result = gson.toJson(data);
+        data2 = gson.fromJson(result, Data.class);
+        assertEquals(data.toString(), data2.toString());
+
+        // should also work with derived types
+        Derived der = new Derived();
+        der.setId(20);
+        der.text = "world";
+        der.unserialized = "abc";
+
+        result = gson.toJson(der);
+
+        // should not contain the unserialized field
+        assertFalse(result.contains("abc"));
+
+        Derived der2 = gson.fromJson(result, Derived.class);
+        der.unserialized = null;
+        assertEquals(der.toString(), der2.toString());
+    }
+
+    @Test
+    public void testCreate_Lists() {
+        DataList lst = new DataList();
+        lst.theList = new ArrayList<>();
+        lst.theList.add(new Data(200, "text 20"));
+        lst.theList.add(new Data(210, "text 21"));
+
+        String result = gson.toJson(lst);
+        assertEquals("{'theList':[{'my-id':200,'text':'text 20'},{'my-id':210,'text':'text 21'}]}".replace('\'', '"'),
+                        result);
+
+        DataList lst2 = gson.fromJson(result, DataList.class);
+        assertEquals(stripIdent(lst.toString()), stripIdent(lst2.toString()));
+        assertEquals(Data.class, lst2.theList.get(0).getClass());
+    }
+
+    @Test
+    public void testCreate_OnlyOutProps() {
+        InFieldIgnored data = new InFieldIgnored();
+        data.value = "out only";
+
+        // field should be serialized
+        String result = gson.toJson(data);
+        assertEquals("{'value':'out only'}".replace('\'', '"'), result);
+
+        // field should NOT be deserialized
+        data = gson.fromJson(result, InFieldIgnored.class);
+        assertNull(data.value);
+    }
+
+    @Test
+    public void testCreate_OnlyInProps() {
+        OutFieldIgnored data = new OutFieldIgnored();
+        data.value = "in only";
+
+        // field should NOT be serialized
+        String result = gson.toJson(data);
+        assertEquals("{}", result);
+
+        // field should NOT be deserialized
+        data = gson.fromJson("{'value':'in only'}".replace('\'', '"'), OutFieldIgnored.class);
+        assertEquals("in only", data.value);
+    }
+
+    /**
+     * Object identifiers may change with each execution, so this method is used to strip
+     * the identifier from the text string so that the strings will still match across
+     * different runs.
+     *
+     * @param text text from which to strip the identifier
+     * @return the text, without the identifier
+     */
+    private String stripIdent(String text) {
+        return text.replaceFirst("@\\w+", "@");
+    }
+
+    private static class Data {
+        @GsonJsonProperty("my-id")
+        private int id;
+
+        public String text;
+
+        public Data() {
+            super();
+        }
+
+        public Data(int id, String text) {
+            this.id = id;
+            this.text = text;
+        }
+
+        public void setId(int id) {
+            this.id = id;
+        }
+
+        @Override
+        public String toString() {
+            return "Data [id=" + id + ", text=" + text + "]";
+        }
+    }
+
+    private static class Derived extends Data {
+        // not serialized
+        private String unserialized;
+
+        @Override
+        public String toString() {
+            return "Derived [unserialized=" + unserialized + ", toString()=" + super.toString() + "]";
+        }
+    }
+
+    private static class DataList {
+        @GsonJsonProperty
+        private List<Data> theList;
+    }
+
+    protected static class NothingToSerialize {
+        // not serialized
+        protected String unserialized;
+    }
+
+    /**
+     * This has a field that should show up in the "output" list, but not in the "input"
+     * list, because the method will override it.
+     */
+    private static class InFieldIgnored {
+        @GsonJsonProperty("value")
+        private String value;
+
+        @GsonJsonIgnore
+        public void setValue(String value) {
+            this.value = value;
+        }
+    }
+
+    /**
+     * This has a field that should show up in the "input" list, but not in the "output"
+     * list, because the method will override it.
+     */
+    private static class OutFieldIgnored {
+        @GsonJsonProperty("value")
+        private String value;
+
+        @GsonJsonIgnore
+        public String getValue() {
+            return value;
+        }
+    }
+}
diff --git a/gson/src/test/java/org/onap/policy/common/gson/internal/FieldDeserializerTest.java b/gson/src/test/java/org/onap/policy/common/gson/internal/FieldDeserializerTest.java
new file mode 100644
index 00000000..62bab231
--- /dev/null
+++ b/gson/src/test/java/org/onap/policy/common/gson/internal/FieldDeserializerTest.java
@@ -0,0 +1,109 @@
+/*
+ * ============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 static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonNull;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import java.util.List;
+import org.junit.Test;
+import org.onap.policy.common.gson.JacksonExclusionStrategy;
+import org.onap.policy.common.gson.internal.DataAdapterFactory.Data;
+import org.onap.policy.common.gson.internal.FieldDeserializer;
+
+public class FieldDeserializerTest {
+    private static final String TEXT_FIELD_NAME = "text";
+    private static final String LIST_FIELD_NAME = "listField";
+    private static final String INITIAL_VALUE = "initial value";
+    private static final String NEW_VALUE = "new value";
+
+    private static DataAdapterFactory dataAdapter = new DataAdapterFactory();
+
+    private static Gson gson = new GsonBuilder().registerTypeAdapterFactory(dataAdapter)
+                    .setExclusionStrategies(new JacksonExclusionStrategy()).create();
+
+    private FieldDeserializer deser;
+
+    private String text;
+
+    private List<Data> listField;
+
+    @Test
+    public void testGetFromTree() throws Exception {
+        deser = new FieldDeserializer(gson, FieldDeserializerTest.class.getDeclaredField(TEXT_FIELD_NAME));
+
+        JsonObject json = new JsonObject();
+
+        // no value in tree - text remains unchanged
+        text = INITIAL_VALUE;
+        deser.getFromTree(json, this);
+        assertEquals(text, INITIAL_VALUE);
+
+        // null value in tree - text remains unchanged
+        json.add(TEXT_FIELD_NAME, JsonNull.INSTANCE);
+        deser.getFromTree(json, this);
+        assertEquals(text, INITIAL_VALUE);
+
+        // now assign a value - text should be changed now
+        json.addProperty(TEXT_FIELD_NAME, NEW_VALUE);
+
+        deser.getFromTree(json, this);
+        assertEquals(text, NEW_VALUE);
+
+        /*
+         * check list field
+         */
+        deser = new FieldDeserializer(gson, FieldDeserializerTest.class.getDeclaredField(LIST_FIELD_NAME));
+
+        json.add(LIST_FIELD_NAME, DataAdapterFactory.makeArray());
+
+        dataAdapter.reset();
+        listField = null;
+        deser.getFromTree(json, this);
+
+        assertTrue(dataAdapter.isDataRead());
+        assertEquals(DataAdapterFactory.makeList().toString(), listField.toString());
+    }
+
+    @Test
+    public void testGetFromTree_SetEx() throws Exception {
+        deser = new FieldDeserializer(gson, FieldDeserializerTest.class.getDeclaredField(TEXT_FIELD_NAME)) {
+            @Override
+            public Object fromJsonTree(JsonElement tree) {
+                // return an int, which won't fit in a String - cause an exception
+                return 10;
+            }
+        };
+
+        JsonObject json = new JsonObject();
+        json.addProperty(TEXT_FIELD_NAME, NEW_VALUE);
+
+        assertThatThrownBy(() -> deser.getFromTree(json, this)).isInstanceOf(JsonParseException.class)
+                        .hasMessage(FieldDeserializer.SET_ERR + FieldDeserializerTest.class.getName() + ".text");
+    }
+}
diff --git a/gson/src/test/java/org/onap/policy/common/gson/internal/FieldSerializerTest.java b/gson/src/test/java/org/onap/policy/common/gson/internal/FieldSerializerTest.java
new file mode 100644
index 00000000..18167fc0
--- /dev/null
+++ b/gson/src/test/java/org/onap/policy/common/gson/internal/FieldSerializerTest.java
@@ -0,0 +1,96 @@
+/*
+ * ============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 static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import java.util.List;
+import org.junit.Test;
+import org.onap.policy.common.gson.JacksonExclusionStrategy;
+import org.onap.policy.common.gson.internal.DataAdapterFactory.Data;
+import org.onap.policy.common.gson.internal.FieldSerializer;
+
+public class FieldSerializerTest {
+    private static final String TEXT_FIELD_NAME = "text";
+    private static final String LIST_FIELD_NAME = "listField";
+
+    private static DataAdapterFactory dataAdapter = new DataAdapterFactory();
+
+    private static Gson gson = new GsonBuilder().registerTypeAdapterFactory(dataAdapter)
+                    .setExclusionStrategies(new JacksonExclusionStrategy()).create();
+
+    private FieldSerializer ser;
+
+    protected String text;
+
+    private List<Data> listField;
+
+    @Test
+    public void testAddToTree() throws Exception {
+        ser = new FieldSerializer(gson, FieldSerializerTest.class.getDeclaredField(TEXT_FIELD_NAME));
+
+        // serialize null value first
+        text = null;
+
+        JsonObject json = new JsonObject();
+        ser.addToTree(this, json);
+        assertTrue(json.get(TEXT_FIELD_NAME).isJsonNull());
+
+        // serialize an actual value
+        text = "hello";
+        ser.addToTree(this, json);
+        assertEquals("hello", json.get(TEXT_FIELD_NAME).getAsString());
+
+        /*
+         * check list field
+         */
+        listField = DataAdapterFactory.makeList();
+
+        ser = new FieldSerializer(gson, FieldSerializerTest.class.getDeclaredField(LIST_FIELD_NAME));
+
+        dataAdapter.reset();
+        JsonElement tree = ser.toJsonTree(listField);
+        assertTrue(dataAdapter.isDataWritten());
+        assertEquals(DataAdapterFactory.ENCODED_LIST, tree.toString());
+    }
+
+    @Test
+    public void testAddToTree_GetEx() throws Exception {
+        ser = new FieldSerializer(gson, FieldSerializerTest.class.getDeclaredField(TEXT_FIELD_NAME)) {
+            @Override
+            protected Object getFromObject(Object source) throws IllegalAccessException {
+                throw new IllegalAccessException("expected exception");
+            }
+        };
+
+        text = "world";
+
+        assertThatThrownBy(() -> ser.addToTree(this, new JsonObject())).isInstanceOf(JsonParseException.class)
+                        .hasMessage(FieldSerializer.GET_ERR + FieldSerializerTest.class.getName() + ".text");
+    }
+}