Complete #638 implementation

release-notes/VERSION

@@ -51,6 +51,8 @@ Project: jackson-databind
 #634: Add `typeFromId(DatabindContext,String)` in `TypeIdDeserializer`
 #636: `ClassNotFoundException` for classes not (yet) needed during serialization
  (contributed by mspiegel@github)
+#638: Add annotation-based method(s) for injecting properties during serialization
+  (using @JsonAppend, VirtualBeanPropertyWriter)
 - Allow use of `Shape.ARRAY` for Enums, as an alias to 'use index'
 - Start using `JsonGenerator.writeStartArray(int)` to help data formats
   that benefit from knowing number of elements in arrays (and would otherwise

src/main/java/com/fasterxml/jackson/databind/ser/BeanPropertyWriter.java

@@ -194,14 +194,17 @@ public BeanPropertyWriter(BeanPropertyDefinition propDef,
     {
         _member = member;
         _contextAnnotations = contextAnnotations;
+
         _name = new SerializedString(propDef.getName());
         _wrapperName = propDef.getWrapperName();
+        _metadata = propDef.getMetadata();
+        _includeInViews = propDef.findViews();
+
         _declaredType = declaredType;
         _serializer = (JsonSerializer<Object>) ser;
         _dynamicSerializers = (ser == null) ? PropertySerializerMap.emptyMap() : null;
         _typeSerializer = typeSer;
         _cfgSerializationType = serType;
-        _metadata = propDef.getMetadata();
 
         if (member instanceof AnnotatedField) {
             _accessorMethod = null;
@@ -210,18 +213,47 @@ public BeanPropertyWriter(BeanPropertyDefinition propDef,
             _accessorMethod = (Method) member.getMember();
             _field = null;
         } else {
-            // 01-Dec-2014, tatu: Used to be illegal, but now explicitly allowed
+            // 01-Dec-2014, tatu: Used to be illegal, but now explicitly allowed for virtual props
             _accessorMethod = null;
             _field = null;
         }
         _suppressNulls = suppressNulls;
         _suppressableValue = suppressableValue;
-        _includeInViews = propDef.findViews();
 
         // this will be resolved later on, unless nulls are to be suppressed
         _nullSerializer = null;
     }
-
+
+    /**
+     * Constructor that may be of use to virtual properties, when there is need for
+     * the zero-arg ("default") constructor, and actual initialization is done
+     * after constructor call.
+     * 
+     * @since 2.5
+     */
+    protected BeanPropertyWriter() {
+        _member = null;
+        _contextAnnotations = null;
+
+        _name = null;
+        _wrapperName = null;
+        _metadata = null;
+        _includeInViews = null;
+
+        _declaredType = null;
+        _serializer = null;
+        _dynamicSerializers = null;
+        _typeSerializer = null;
+        _cfgSerializationType = null;
+
+        _accessorMethod = null;
+        _field = null;
+        _suppressNulls = false;
+        _suppressableValue = null;
+
+        _nullSerializer = null;
+    }
+
     /**
      * "Copy constructor" to be used by filtering sub-classes
      */

src/main/java/com/fasterxml/jackson/databind/ser/VirtualBeanPropertyWriter.java

@@ -17,17 +17,31 @@
  * to add "virtual" properties in addition to regular ones.
  * 
  * @since 2.5
+ * 
+ * @see com.fasterxml.jackson.databind.ser.impl.AttributePropertyWriter
  */
 public abstract class VirtualBeanPropertyWriter
     extends BeanPropertyWriter
 {
+    /**
+     * Constructor used by most sub-types.
+     */
     protected VirtualBeanPropertyWriter(BeanPropertyDefinition propDef,
-            Annotations contextAnnotations, JavaType declaredType,
-            JsonSerializer<?> ser, TypeSerializer typeSer, JavaType serType) {
-        this(propDef, contextAnnotations, declaredType, ser, typeSer, serType,
+            Annotations contextAnnotations, JavaType declaredType)
+    {
+        this(propDef, contextAnnotations, declaredType, null, null, null,
                 propDef.findInclusion());
     }
 
+    /**
+     * Constructor that may be used by sub-classes for constructing a "blue-print" instance;
+     * one that will only become (or create) actual usable instance when its
+     * {@link #withConfig} method is called.
+     */
+    protected VirtualBeanPropertyWriter() {
+        super();
+    }
+
     /**
      * Pass-through constructor that may be used by sub-classes that
      * want full control over implementation.
@@ -61,7 +75,7 @@ protected static Object _suppressableValue(JsonInclude.Include inclusion) {
         }
         return null;
     }
-    
+
     /*
     /**********************************************************
     /* Standard accessor overrides
@@ -98,13 +112,13 @@ public Type getGenericPropertyType() {
 
     /**
      * Contextualization method called on a newly constructed virtual bean property.
-     * If information is used to change behavior, it is recommended that a new instance
-     * is constructed with given information and returned; however, this is not mandatory
-     * and modifying (and returning) this instance is legal as well as calls are made
-     * in thread-safe manner.
+     * Usually a new intance needs to be created due to finality of some of configuration
+     * members; otherwise while recommended, creating a new instance is not strictly-speaking
+     * mandatory because calls are made in thread-safe manner, as part of initialization
+     * before use.
      *
      * @param config Currenct configuration; guaranteed to be {@link SerializationConfig}
-     *   (but not typed since caller does not have full typing)
+     *   (just not typed since caller does not have dependency to serialization-specific types)
      * @param declaringClass Class that contains this property writer
      * @param propDef Nominal property definition to use
      * @param type Declared type for the property

src/test/java/com/fasterxml/jackson/databind/ser/TestVirtualProperties.java

@@ -3,10 +3,14 @@
 import java.util.*;
 
 import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.core.JsonGenerator;
 
-import com.fasterxml.jackson.databind.BaseMapTest;
-import com.fasterxml.jackson.databind.ObjectWriter;
+import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JsonAppend;
+import com.fasterxml.jackson.databind.cfg.MapperConfig;
+import com.fasterxml.jackson.databind.introspect.AnnotatedClass;
+import com.fasterxml.jackson.databind.introspect.BeanPropertyDefinition;
+import com.fasterxml.jackson.databind.util.Annotations;
 
 /**
  * Tests for verifying that one can append virtual properties after regular ones.
@@ -26,10 +30,10 @@ static class SimpleBean
     @JsonAppend(prepend=true, attrs={ @JsonAppend.Attr("id"),
             @JsonAppend.Attr(value="internal", propName="extra")
         })
-        static class SimpleBeanPrepend
-        {
-            public int value = 13;
-        }
+    static class SimpleBeanPrepend
+    {
+        public int value = 13;
+    }
 
     enum ABC {
         A, B, C;
@@ -40,6 +44,44 @@ static class OptionalsBean
     {
         public int value = 28;
     }
+
+    static class CustomVProperty
+        extends VirtualBeanPropertyWriter
+    {
+        private CustomVProperty() { super(); }
+
+        private CustomVProperty(BeanPropertyDefinition propDef,
+                Annotations ctxtAnn, JavaType type) {
+            super(propDef, ctxtAnn, type);
+        }
+
+        @Override
+        protected Object value(Object bean, JsonGenerator jgen, SerializerProvider prov) {
+            if (_name.toString().equals("id")) {
+                return "abc123";
+            }
+            if (_name.toString().equals("extra")) {
+                return new int[] { 42 };
+            }
+            return "???";
+        }
+
+        @Override
+        public VirtualBeanPropertyWriter withConfig(MapperConfig<?> config,
+                AnnotatedClass declaringClass, BeanPropertyDefinition propDef,
+                JavaType type)
+        {
+            return new CustomVProperty(propDef, declaringClass.getAnnotations(), type);
+        }
+    }
+
+    @JsonAppend(prepend=true, props={ @JsonAppend.Prop(value=CustomVProperty.class, name="id"),
+            @JsonAppend.Prop(value=CustomVProperty.class, name="extra")
+        })
+    static class CustomVBean
+    {
+        public int value = 72;
+    }
 
     /*
     /**********************************************************
@@ -82,4 +124,11 @@ public void testAttributePropInclusion() throws Exception
                 .writeValueAsString(new OptionalsBean());
         assertEquals(aposToQuotes("{'value':28}"), json);
     }
+
+    public void testCustomProperties() throws Exception
+    {
+        String json = WRITER.withAttribute("desc", "nice")
+                .writeValueAsString(new CustomVBean());
+        assertEquals(aposToQuotes("{'id':'abc123','extra':[42],'value':72}"), json);
+    }
 }