Fix #5045 (#5301)

Author: cowtowncoder

release-notes/CREDITS-2.x

@@ -11,6 +11,7 @@ Co-Authors (with only partial listings below):
 * Joo Hyuk Kim (@JooHyukKim)
 * PJ Fanning (@pjfanning)
 * Sim Yih Tsern (@yihtsern)
+* wrongwrong (@k163377)
 
 ----------------------------------------------------------------------------
 
@@ -1526,7 +1527,7 @@ PJ Fanning (pjfanning@github)
   * Contributed #3530: Change LRUMap to just evict one entry when maxEntries reached
   (2.14.0)
   * Contributed #3837: Set transformer factory attributes to improve protection against XXE
-  (2.14.3)
+  (2.14.3
   - And NUMEROUS other contributions not listed here! (for 2.15 and above)
 
 Igor Shymko (ancane@github)
@@ -1872,6 +1873,7 @@ wrongwrong (@k163377)
  * Reported #4218: If `@JacksonInject` is specified for field and deserialized by
    the Creator, the inject process will be executed twice
   (2.20.0)
+ - And many other contributions not listed here! (for 2.21 and above)
 
 Bernd Ahlers (@bernd)
  * Reported #4742: Deserialization with Builder, External type id, `@JsonCreator` failing

release-notes/VERSION-2.x

@@ -6,6 +6,9 @@ Project: jackson-databind
 
 2.21.0 (not yet released)
 
+#5045: If there is a no-parameter constructor marked as `JsonCreator` and
+  a constructor reported as `DefaultCreator`, latter is incorrectly used
+ (reported by  @wrongwrong)
 #5293: Fix minor typo in `PropertyBindingException.getMessageSuffix()`
  (reported by Johny L)
 

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

@@ -690,6 +690,13 @@ protected void _addCreators(Map<String, POJOPropertyBuilder> props)
         List<PotentialCreator> constructors = _collectCreators(_classDef.getConstructors());
         List<PotentialCreator> factories = _collectCreators(_classDef.getFactoryMethods());
 
+        // Note! 0-param ("default") constructor is NOT included in 'constructors':
+        PotentialCreator zeroParamsConstructor;
+        {
+            AnnotatedConstructor ac = _classDef.getDefaultConstructor();
+            zeroParamsConstructor = (ac == null) ? null : _potentialCreator(ac);
+        }
+
         // Then find what is the Primary Constructor (if one exists for type):
         // for Java Records and potentially other types too ("data classes"):
         // Needs to be done early to get implicit names populated
@@ -699,20 +706,30 @@ protected void _addCreators(Map<String, POJOPropertyBuilder> props)
         } else {
             // 02-Nov-2024, tatu: Alas, naming here is confusing: method properly
             //    should have been "findPrimaryCreator()" so as not to confused with
-            //    0-args default Creators...
+            //    0-param default Creators...
             primaryCreator = _annotationIntrospector.findDefaultCreator(_config, _classDef,
                     constructors, factories);
         }
         // Next: remove creators marked as explicitly disabled
         _removeDisabledCreators(constructors);
         _removeDisabledCreators(factories);
-        
+        if (zeroParamsConstructor != null && _isDisabledCreator(zeroParamsConstructor)) {
+            zeroParamsConstructor = null;
+        }
+
         // And then remove non-annotated static methods that do not look like factories
         _removeNonFactoryStaticMethods(factories, primaryCreator);
 
         // and use annotations to find explicitly chosen Creators
         if (_useAnnotations) { // can't have explicit ones without Annotation introspection
-            // Start with Constructors as they have higher precedence:
+            // Start with Constructors as they have higher precedence
+
+            // 08-Sep-2025, tatu: [databind#5045] Need to ensure 0-param ("default")
+            //   constructor considered if annotated (disabled case handled above).
+            if (zeroParamsConstructor != null && zeroParamsConstructor.isAnnotated()) {
+                creators.setPropertiesBased(_config, zeroParamsConstructor, "explicit");
+            }
+
             _addExplicitlyAnnotatedCreators(creators, constructors, props, false);
             // followed by Factory methods (lower precedence)
             _addExplicitlyAnnotatedCreators(creators, factories, props,
@@ -753,7 +770,7 @@ protected void _addCreators(Map<String, POJOPropertyBuilder> props)
         final ConstructorDetector ctorDetector = _config.getConstructorDetector();
         if (!creators.hasPropertiesBasedOrDelegating()
                 && !ctorDetector.requireCtorAnnotation()) {
-            // But only if no Default (0-args) constructor available OR if we are configured
+            // But only if no Default (0-params) constructor available OR if we are configured
             // to prefer properties-based Creators
             if ((_classDef.getDefaultConstructor() == null)
                     || ctorDetector.singleArgCreatorDefaultsToProperties()) {
@@ -809,25 +826,33 @@ private List<PotentialCreator> _collectCreators(List<? extends AnnotatedWithPara
         }
         List<PotentialCreator> result = new ArrayList<>();
         for (AnnotatedWithParams ctor : ctors) {
-            JsonCreator.Mode creatorMode = _useAnnotations
-                    ? _annotationIntrospector.findCreatorAnnotation(_config, ctor) : null;
             // 06-Jul-2024, tatu: Can't yet drop DISABLED ones; add all (for now)
-            result.add(new PotentialCreator(ctor, creatorMode));
+            result.add(_potentialCreator(ctor));
         }
         return (result == null) ? Collections.emptyList() : result;
     }
 
+    private PotentialCreator _potentialCreator(AnnotatedWithParams ctor) {
+        final JsonCreator.Mode creatorMode = _useAnnotations
+                ? _annotationIntrospector.findCreatorAnnotation(_config, ctor) : null;
+        return new PotentialCreator(ctor, creatorMode);
+    }
+
     private void _removeDisabledCreators(List<PotentialCreator> ctors)
     {
         Iterator<PotentialCreator> it = ctors.iterator();
         while (it.hasNext()) {
-            // explicitly prevented? Remove
-            if (it.next().creatorMode() == JsonCreator.Mode.DISABLED) {
+            // explicitly disabled? Remove
+            if (_isDisabledCreator(it.next())) {
                 it.remove();
             }
         }
     }
 
+    private boolean _isDisabledCreator(PotentialCreator ctor) {
+         return ctor.creatorMode() == JsonCreator.Mode.DISABLED;
+    }
+
     private void _removeNonVisibleCreators(List<PotentialCreator> ctors)
     {
         Iterator<PotentialCreator> it = ctors.iterator();

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

@@ -24,7 +24,7 @@ public PotentialCreators() { }
     /**********************************************************************
      */
 
-    // desc -> "explicit", "implicit" etc
+    // mode -> "explicit", "implicit" etc
     public void setPropertiesBased(MapperConfig<?> config, PotentialCreator ctor, String mode)
     {
         if (propertiesBased != null) {

src/test/java/com/fasterxml/jackson/databind/deser/creators/NoParamsCreatorDefault5045Test.java

@@ -0,0 +1,61 @@
+package com.fasterxml.jackson.databind.deser.creators;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.cfg.MapperConfig;
+import com.fasterxml.jackson.databind.introspect.AnnotatedClass;
+import com.fasterxml.jackson.databind.introspect.PotentialCreator;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+import com.fasterxml.jackson.databind.testutil.DatabindTestUtil;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+public class NoParamsCreatorDefault5045Test extends DatabindTestUtil
+{
+    static class User5045 {
+        public int age;
+
+        public User5045(@ImplicitName("age") int age) {
+            throw new IllegalStateException("Should not be called");
+        }
+
+        @JsonCreator
+        public User5045() { 
+            this.age = -1;
+        }
+
+        public int getAge() { return age; }
+    }
+
+    @SuppressWarnings("serial")
+    static class AI5045 extends ImplicitNameIntrospector {
+        @Override
+        public PotentialCreator findDefaultCreator(MapperConfig<?> config,
+                AnnotatedClass valueClass,
+                List<PotentialCreator> declaredConstructors,
+                List<PotentialCreator> declaredFactories)
+        {
+            for (PotentialCreator pc : declaredConstructors) {
+                if (pc.paramCount() != 0) {
+                    return pc;
+                }
+            }
+            return null;
+        }
+    }
+
+    @Test
+    public void defaultCreator5045() throws Exception {
+        ObjectMapper mapper = JsonMapper.builder().annotationIntrospector(new AI5045()).build();
+        String json = "{ }";
+
+        User5045 user = mapper.readValue(json, User5045.class);
+        assertNotNull(user);
+        assertEquals(-1, user.getAge());
+    }    
+}