Fix #2657

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -47,6 +47,7 @@ Project: jackson-databind
 #2643: Change default textual serialization of `java.util.Date`/`Calendar`
   to include colon in timezone offset
 #2647: Add `ObjectMapper.createParser()` and `createGenerator()` methods
+#2657: Allow serialization of `Properties` with non-String values
 #2663: Add new factory method for creating custom `EnumValues` to pass to `EnumDeserializer
  (requested by Rafal K)
 - Add `SerializerProvider.findContentValueSerializer()` methods

src/main/java/com/fasterxml/jackson/databind/ser/std/MapSerializer.java

@@ -304,12 +304,18 @@ public static MapSerializer construct(Set<String> ignoredEntries, JavaType mapTy
             Object filterId)
     {
         JavaType keyType, valueType;
-        
+
         if (mapType == null) {
             keyType = valueType = UNSPECIFIED_TYPE;
         } else { 
             keyType = mapType.getKeyType();
-            valueType = mapType.getContentType();
+            if (mapType.hasRawClass(java.util.Properties.class)) {
+                // 25-Mar-2020, tatu: [databind#2657] Since non-standard Properties may actually
+                //     contain non-Strings, demote value type to raw `Object`
+                valueType = TypeFactory.unknownType();
+            } else {
+                valueType = mapType.getContentType();
+            }
         }
         // If value type is final, it's same as forcing static value typing:
         if (!staticValueType) {

src/test/java/com/fasterxml/jackson/databind/ser/jdk/JDKTypeSerializationTest.java

@@ -222,4 +222,15 @@ public void testVoidSerialization() throws Exception
         assertEquals(aposToQuotes("{'value':null}"),
                 MAPPER.writeValueAsString(new VoidBean()));
     }
+
+    // [databind#2657]
+    public void testNonStandardProperties() throws Exception
+    {
+        Properties properties = new Properties();
+        // Bad usage: Properties should NOT contain non-Strings. But
+        // some do that regardless and compiler won't stop it so.
+        properties.put("key", 1);
+        String json = MAPPER.writeValueAsString(properties);
+        assertEquals("{\"key\":1}", json);
+    }
 }