RFE-4650: Single string value primitive array deserialization improvement

release-notes/VERSION-2.x

@@ -20,6 +20,9 @@ Project: jackson-databind
  (contributed by Geoffrey G)
 #4388: Allow using `@JsonPropertyOrder` with "any" (`@JsonAnyGetter`)  properties
  (fix by Joo-Hyuk K)
+#4650: `PrimitiveArrayDeserializers` should deal with single String value if
+  `DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY` enabled
+ (reported, fix suggested by @eeren-bm)
 #4674: Allow setting global enum naming strategy similar to property naming strategy
  (requested by @hajdamak)
  (contributed by Konstantin M)

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

@@ -213,13 +213,19 @@ public T deserialize(JsonParser p, DeserializationContext ctxt, T existing) thro
     @SuppressWarnings("unchecked")
     protected T handleNonArray(JsonParser p, DeserializationContext ctxt) throws IOException
     {
-        // Empty String can become null...
-        if (p.hasToken(JsonToken.VALUE_STRING)) {
-            return _deserializeFromString(p, ctxt);
-        }
-        boolean canWrap = (_unwrapSingle == Boolean.TRUE) ||
+
+        final boolean canWrap = (_unwrapSingle == Boolean.TRUE) ||
                 ((_unwrapSingle == null) &&
                         ctxt.isEnabled(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY));
+        // 12-Mar-2025, tatu: as per [databind#4650] things get bit tricky with
+        //   single-element wrapping of a String value
+        // Let's still call _deserializeFromString() for empty strings no matter what,
+        // and for all values if wrapping not enabled
+        if (p.hasToken(JsonToken.VALUE_STRING)) {
+            if (!canWrap || _isBlank(p.getText())) {
+                return _deserializeFromString(p, ctxt);
+            }
+        }
         if (canWrap) {
             return handleSingleElementUnwrapped(p, ctxt);
         }

src/test/java/com/fasterxml/jackson/databind/deser/jdk/ArrayDeserializationTest.java

@@ -12,6 +12,7 @@
 import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 
+import static com.fasterxml.jackson.databind.DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY;
 import static org.junit.jupiter.api.Assertions.*;
 
 import static com.fasterxml.jackson.databind.testutil.DatabindTestUtil.a2q;
@@ -542,6 +543,53 @@ public void testFloatArray() throws Exception
         }
     }
 
+    @Test
+    public void testSingleStringToPrimitiveArray() throws JsonProcessingException {
+        MAPPER.enable(ACCEPT_SINGLE_VALUE_AS_ARRAY);
+        assertLengthValue(MAPPER.readValue("\"true\"", boolean[].class), true);
+        assertLengthValue(MAPPER.readValue("\"a\"", char[].class), 'a');
+        assertLengthValue(MAPPER.readValue("\"1\"", short[].class), (short) 1);
+        assertLengthValue(MAPPER.readValue("\"1\"", int[].class), 1);
+        assertLengthValue(MAPPER.readValue("\"1\"", long[].class), 1L);
+        assertLengthValue(MAPPER.readValue("\"7.038531e-26\"", float[].class), 7.038531e-26f);
+        assertLengthValue(MAPPER.readValue("\"1.5555\"", double[].class), 1.5555d);
+    }
+
+    private void assertLengthValue(boolean[] arr, boolean expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
+    private void assertLengthValue(char[] arr, char expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
+    private void assertLengthValue(short[] arr, short expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
+    private void assertLengthValue(int[] arr, int expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
+    private void assertLengthValue(long[] arr, long expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
+    private void assertLengthValue(float[] arr, float expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
+    private void assertLengthValue(double[] arr, double expt) {
+        assertEquals(1, arr.length);
+        assertEquals(expt, arr[0]);
+    }
+
     /*
     /**********************************************************
     /* Tests for Bean arrays