Fix #66

Author: cowtowncoder

release-notes/VERSION

@@ -6,6 +6,10 @@ Project: jackson-datatype-guava
 
 2.6.0 (not yet released)
 
+#66: Add `GuavaModule.configureAbsentsAsNulls(boolean)` to change whether
+ `Optional.absent()` is to be handled same as Java null during serialization
+ (default: true) or not.
+
 2.5.4 (not yet released)
 
 2.5.3 (24-Apr-2015)

src/main/java/com/fasterxml/jackson/datatype/guava/GuavaModule.java

@@ -8,6 +8,21 @@
 public class GuavaModule extends Module // can't use just SimpleModule, due to generic types
 {
     private final String NAME = "GuavaModule";
+
+    /**
+     * Configuration setting that determines whether `Optional.absent()` is
+     * considered "same as null" for serialization purposes; that is, to be
+     * filtered same as nulls are.
+     * If enabled, absent values are treated like nulls; if disabled, they are not.
+     * In either case, absent values are always considered "empty".
+     *<p>
+     * Default value is `true` for backwards compatibility (2.5 and prior
+     * only had this behavior).
+     *<p>
+     * Note that this setting MUST be changed BEFORE registering the module:
+     * changes after registration will have no effect.
+     */
+    protected boolean _cfgHandleAbsentAsNull = true;
 
     public GuavaModule() {
         super();
@@ -22,9 +37,31 @@ public void setupModule(SetupContext context)
         context.addDeserializers(new GuavaDeserializers());
         context.addSerializers(new GuavaSerializers());
         context.addTypeModifier(new GuavaTypeModifier());
-        context.addBeanSerializerModifier(new GuavaBeanSerializerModifier());
+
+        // 28-Apr-2015, tatu: Allow disabling "treat Optional.absent() like Java nulls"
+        if (_cfgHandleAbsentAsNull) {
+            context.addBeanSerializerModifier(new GuavaBeanSerializerModifier());
+        }
     }
 
+    /**
+     * Configuration method that may be used to change configuration setting
+     * {@link #_cfgHandleAbsentAsNull}: enabling means that `Optional.absent()` values
+     * are handled like Java nulls (wrt filtering on serialization); disabling that
+     * they are only treated as "empty" values, but not like native Java nulls.
+     * Recommended setting for this value is `false`, for compatibility with other
+     * "optional" values (like JDK 8 optionals); but the default is `true` for
+     * backwards compatibility.
+     * 
+     * @return This module instance, useful for chaining calls
+     * 
+     * @since 2.6
+     */
+    public GuavaModule configureAbsentsAsNulls(boolean state) {
+        _cfgHandleAbsentAsNull = state;
+        return this;
+    }
+    
     @Override
     public int hashCode()
     {

src/main/java/com/fasterxml/jackson/datatype/guava/ser/GuavaBeanSerializerModifier.java

@@ -8,8 +8,12 @@
 
 import java.util.List;
 
-public class GuavaBeanSerializerModifier extends BeanSerializerModifier {
-
+/**
+ * {@link BeanSerializerModifier} needed to sneak in handler to exclude "absent"
+ * optional values iff handling of "absent as nulls" is enabled.
+ */
+public class GuavaBeanSerializerModifier extends BeanSerializerModifier
+{
     @Override
     public List<BeanPropertyWriter> changeProperties(SerializationConfig config,
             BeanDescription beanDesc,

src/main/java/com/fasterxml/jackson/datatype/guava/ser/GuavaOptionalSerializer.java

@@ -84,7 +84,7 @@ public JsonSerializer<?> createContextual(SerializerProvider provider,
 
     @Override
     public void serialize(Optional<?> value, JsonGenerator jgen, SerializerProvider provider)
-            throws IOException
+        throws IOException
     {
         if (value.isPresent()) {
             if (_valueSerializer != null) {

src/test/java/com/fasterxml/jackson/datatype/guava/TestOptional.java

@@ -16,7 +16,7 @@ public class TestOptional extends ModuleTestBase
     private final ObjectMapper MAPPER = mapperWithModule();
 
     @JsonAutoDetect(fieldVisibility=Visibility.ANY)
-    public static final class OptionalData{
+    public static final class OptionalData {
         private Optional<String> myString;
     }
 
@@ -122,14 +122,34 @@ public void testSerOptDefault() throws Exception {
         String value = mapperWithModule().setSerializationInclusion(JsonInclude.Include.ALWAYS).writeValueAsString(data);
         assertEquals("{\"myString\":null}", value);
     }
-    
+
     public void testSerOptNull() throws Exception {
         OptionalData data = new OptionalData();
         data.myString = null;
         String value = mapperWithModule().setSerializationInclusion(JsonInclude.Include.NON_NULL).writeValueAsString(data);
         assertEquals("{}", value);
     }
 
+    // for [dataformat-guava#66]
+    public void testSerOptDisableAsNull() throws Exception {
+        final OptionalData data = new OptionalData();
+        data.myString = Optional.absent();
+
+        GuavaModule mod = new GuavaModule().configureAbsentsAsNulls(false);
+        ObjectMapper mapper = new ObjectMapper()
+            .registerModule(mod)
+            .setSerializationInclusion(JsonInclude.Include.NON_NULL);
+
+        assertEquals("{\"myString\":null}", mapper.writeValueAsString(data));
+
+        // but do exclude with NON_EMPTY
+        mapper = new ObjectMapper()
+            .registerModule(mod)
+            .setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
+
+        assertEquals("{}", mapper.writeValueAsString(data));
+    }
+    
     public void testSerOptNonEmpty() throws Exception {
         OptionalData data = new OptionalData();
         data.myString = null;