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>

1 files changed, 80 insertions, 0 deletions

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);
+    }
+}