Implement #3676

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -4,6 +4,11 @@ Project: jackson-databind
 === Releases === 
 ------------------------------------------------------------------------
 
+2.15.0 (not yet released)
+
+#3676: Allow use of `@JsonCreator(mode = Mode.PROPERTIES)` creator for POJOs
+ with"empty String" coercion
+
 2.14.1 (not yet released)
 
 #3655: `Enum` values can not be read from single-element array even with

src/main/java/com/fasterxml/jackson/databind/deser/BeanDeserializerBase.java

@@ -1039,7 +1039,11 @@ public AccessPattern getEmptyAccessPattern() {
     public Object getEmptyValue(DeserializationContext ctxt) throws JsonMappingException {
         // alas, need to promote exception, if any:
         try {
-            return _valueInstantiator.createUsingDefault(ctxt);
+            // 20-Nov-2022, tatu: Ok one more complication; may want to consider
+            //     EITHER default Creator OR properties-one with no args.
+            //     But that is encapsulated by `ValueInstantiator` now
+            // return _valueInstantiator.createUsingDefault(ctxt);
+            return _valueInstantiator.createUsingDefaultOrWithoutArguments(ctxt);
         } catch (IOException e) {
             return ClassUtil.throwAsMappingException(ctxt, e);
         }

src/main/java/com/fasterxml/jackson/databind/deser/ValueInstantiator.java

@@ -263,6 +263,19 @@ public Object createFromObjectWith(DeserializationContext ctxt, Object[] args) t
                 "no creator with arguments specified");
     }
 
+    /**
+     * Combination of {@link #createUsingDefault} and {@link #createFromObjectWith(DeserializationContext, Object[])}
+     * which will call former first, if possible; or latter if possible (with {@code null}
+     * arguments); and if neither works throw an exception.
+     *
+     * @since 2.15
+     */
+    //public abstract Object createUsingDefaultOrWithoutArguments(DeserializationContext ctxt) throws IOException;
+    public Object createUsingDefaultOrWithoutArguments(DeserializationContext ctxt) throws IOException {
+        return ctxt.handleMissingInstantiator(getValueClass(), this, null,
+                "neither default (no-arguments) nor with-arguments Creator found");
+    }
+
     /**
      * Method that delegates to
      * {@link #createFromObjectWith(DeserializationContext, Object[])} by

src/main/java/com/fasterxml/jackson/databind/deser/std/StdValueInstantiator.java

@@ -294,6 +294,17 @@ public Object createFromObjectWith(DeserializationContext ctxt, Object[] args) t
         }
     }
 
+    @Override
+    public Object createUsingDefaultOrWithoutArguments(DeserializationContext ctxt) throws IOException {
+        if (_defaultCreator != null) { // sanity-check; caller should check
+            return createUsingDefault(ctxt);
+        }
+        if (_withArgsCreator != null) {
+            return createFromObjectWith(ctxt, new Object[_constructorArguments.length]);
+        }
+        return super.createUsingDefaultOrWithoutArguments(ctxt);
+    }
+
     @Override
     public Object createUsingDelegate(DeserializationContext ctxt, Object delegate) throws IOException
     {

src/test/java/com/fasterxml/jackson/databind/convert/CoercePojosTest.java

@@ -1,5 +1,7 @@
 package com.fasterxml.jackson.databind.convert;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JacksonException;
 
 import com.fasterxml.jackson.databind.*;
@@ -14,11 +16,20 @@ static class Bean {
         public String a;
     }
 
-    private final ObjectMapper MAPPER = newJsonMapper();
+    static class BeanWithProp3676 {
+        @JsonCreator
+        public BeanWithProp3676(@JsonProperty("a") String a) {
+            this.a = a;
+        }
+
+        public String a;
+    }
 
     private final String JSON_EMPTY = q("");
     private final String JSON_BLANK = q("    ");
 
+    private final ObjectMapper MAPPER = newJsonMapper();
+
     /*
     /********************************************************
     /* Test methods, from empty String
@@ -52,6 +63,22 @@ public void testPOJOFromEmptyPhysicalTypeConfig() throws Exception
         _testPOJOFromEmptyPhysicalTypeConfig(CoercionInputShape.EmptyString, JSON_EMPTY, null);
     }
 
+    // [databind#3676] Alternative test for "Mode.PROPERTIES" variant where we
+    //  have no "default" constructor
+    public void testPOJOFromEmptyWithProperties() throws Exception
+    {
+        // Then coerce as empty
+        ObjectMapper mapper = jsonMapperBuilder()
+                .withCoercionConfigDefaults(h -> {
+                    h.setCoercion(CoercionInputShape.EmptyString, CoercionAction.AsEmpty);
+                })
+            .build();
+        BeanWithProp3676 b = mapper.readerFor(BeanWithProp3676.class)
+                .readValue(JSON_EMPTY);
+        assertNotNull(b);
+        assertNull(b.a);
+    }
+
     /*
     /********************************************************
     /* Test methods, from blank String