Enhancement [JOHNZON-278] Return constant instead of new instance of empty block / empty array

Even in these days of modern Java, reducing memory consumption, GC stress and memory fragmentation, are beneficial side aspects.

If makes no sense to create new empty instances of JsonArray and JsonObject again and again. For this case, JSON-P provides special constants.

It makes sense to return these constants always.

Signed-off-by: Markus KARG <markus@headcrashing.eu>

Author: mkarg

johnzon-core/src/main/java/org/apache/johnzon/core/JsonArrayBuilderImpl.java

@@ -298,7 +298,7 @@ public JsonArrayBuilder add(final JsonArrayBuilder builder) {
         addValue(builder.build());
         return this;
     }
-    
+
     private void setValue(int idx, JsonValue value) {
         if (value == null || tmpList == null) {
             throw npe();
@@ -333,7 +333,7 @@ private void addValue(int idx, JsonValue value) {
     @Override
     public JsonArray build() {
         if(tmpList == null) {
-            return new JsonArrayImpl(Collections.emptyList(), bufferProvider);
+            return JsonValue.EMPTY_JSON_ARRAY;
         }
         return new JsonArrayImpl(Collections.unmodifiableList(tmpList), bufferProvider);
     }

johnzon-core/src/main/java/org/apache/johnzon/core/JsonObjectBuilderImpl.java

@@ -176,16 +176,16 @@ private void putValue(String name, JsonValue value){
         if(name == null || value == null) {
             throw new NullPointerException("name or value/builder must not be null");
         }
-        
+
         attributeMap.put(name, value);
     }
-    
+
 
     @Override
     public JsonObject build() {
-        
+
         if(attributeMap == null || attributeMap.isEmpty()) {
-            return new JsonObjectImpl(Collections.EMPTY_MAP, bufferProvider);
+            return JsonValue.EMPTY_JSON_OBJECT;
         } else {
             Map<String, JsonValue> dump = (Collections.unmodifiableMap(attributeMap));
             return new JsonObjectImpl(dump, bufferProvider);

pom.xml

@@ -36,7 +36,7 @@
   <url>http://johnzon.apache.org</url>
 
   <properties>
-    <geronimo-jsonp.version>1.2</geronimo-jsonp.version>
+    <geronimo-jsonp.version>1.3-SNAPSHOT</geronimo-jsonp.version>
     <geronimo-jsonb.version>1.2</geronimo-jsonb.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <johnzon.site.url>https://svn.apache.org/repos/asf/johnzon/site/publish/</johnzon.site.url>