Merge branch '2.10' into 2.11

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/introspect/SimpleMixInResolver.java

@@ -99,4 +99,33 @@ public Class<?> findMixInClassFor(Class<?> cls)
     public int localSize() {
         return (_localMixIns == null) ? 0 : _localMixIns.size();
     }
+
+    /**
+     * Method that may be called for optimization purposes, to see if calls to
+     * mix-in resolver may be avoided. Return value of {@code true} means that
+     * it is possible that a mix-in class will be found; {@code false} that no
+     * mix-in will ever be found. In latter case caller can avoid calls altogether.
+     *<p>
+     * Note that the reason for "empty" resolvers is to use "null object" for simplifying
+     * code.
+     *
+     * @return True, if this resolver MAY have mix-ins to apply; false if not (it
+     *   is "empty")
+     *
+     * @since 2.10.1
+     */
+    public boolean hasMixIns() {
+        if (_localMixIns == null) {
+            // if neither local mix-ins nor overrides, no mix-ins
+            if (_overrides == null) {
+                return false;
+            }
+            // or, if no local mix-ins and can delegate to resolver
+            if (_overrides instanceof SimpleMixInResolver) {
+                return ((SimpleMixInResolver) _overrides).hasMixIns();
+            }
+        }
+        // cannot rule out the possibility, so...
+        return true;
+    }
 }

src/test/java/com/fasterxml/jackson/databind/mixins/TestMixinSerForMethods.java

@@ -6,6 +6,7 @@
 import com.fasterxml.jackson.annotation.*;
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.introspect.ClassIntrospector;
+import com.fasterxml.jackson.databind.introspect.SimpleMixInResolver;
 import com.fasterxml.jackson.databind.introspect.ClassIntrospector.MixInResolver;
 
 public class TestMixinSerForMethods
@@ -147,11 +148,18 @@ public void testIntermediateMixin2() throws IOException
         assertEquals(Integer.valueOf(42), result.get("x"));
     }
 
+    public void testSimpleMixInResolverHasMixins() {
+        SimpleMixInResolver simple = new SimpleMixInResolver(null);
+        assertFalse(simple.hasMixIns());
+        simple.addLocalDefinition(String.class, Number.class);
+        assertTrue(simple.hasMixIns());
+    }
+
     // [databind#688]
     public void testCustomResolver() throws IOException
     {
         ObjectMapper mapper = new ObjectMapper();
-        mapper.setMixInResolver(new ClassIntrospector.MixInResolver() {
+        MixInResolver res = new ClassIntrospector.MixInResolver() {
             @Override
             public Class<?> findMixInClassFor(Class<?> target) {
                 if (target == EmptyBean.class) {
@@ -164,9 +172,13 @@ public Class<?> findMixInClassFor(Class<?> target) {
             public MixInResolver copy() {
                 return this;
             }
-        });
+        };
+        mapper.setMixInResolver(res);
         Map<String,Object> result = writeAndMap(mapper, new SimpleBean());
         assertEquals(1, result.size());
         assertEquals(Integer.valueOf(42), result.get("x"));
+
+        SimpleMixInResolver simple = new SimpleMixInResolver(res);
+        assertTrue(simple.hasMixIns());
     }
 }