#3305 - fix default CharSequence serialization

src/main/java/com/fasterxml/jackson/databind/ser/BeanSerializerFactory.java

@@ -637,6 +637,8 @@ protected List<BeanPropertyWriter> findBeanProperties(SerializerProvider prov,
     protected List<BeanPropertyWriter> filterBeanProperties(SerializationConfig config,
             BeanDescription beanDesc, List<BeanPropertyWriter> props)
     {
+        removeDefaultProperties(props);
+
         // 01-May-2016, tatu: Which base type to use here gets tricky, since
         //   it may often make most sense to use general type for overrides,
         //   but what we have here may be more specific impl type. But for now
@@ -767,6 +769,28 @@ protected void removeSetterlessGetters(SerializationConfig config, BeanDescripti
         }
     }
 
+    /**
+     * Helper method that will remove all properties that are added by default JDK methods,
+     * e.g. java.lang.CharSequence.isEmpty() (since JDK 15).
+     */
+    private void removeDefaultProperties(List<BeanPropertyWriter> properties)
+    {
+        Iterator<BeanPropertyWriter> it = properties.iterator();
+        while (it.hasNext()) {
+            BeanPropertyWriter writer = it.next();
+
+            AnnotatedMember member = writer.getMember();
+            if (member != null) {
+                Class<?> declaringClass = member.getDeclaringClass();
+
+                if (declaringClass == CharSequence.class) {
+                    // #3331 JDK 15 defines CharSequence.isEmpty() method that is treated as property
+                    it.remove();
+                }
+            }
+        }
+    }
+
     /**
      * Helper method called to ensure that we do not have "duplicate" type ids.
      * Added to resolve [databind#222]

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

@@ -0,0 +1,64 @@
+package com.fasterxml.jackson.databind.ser.jdk;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class CharSequenceSerializationTest {
+
+    private static final String APP_ID = "3074457345618296002";
+
+    @Test
+    public void objectMapperShouldSerializeAsJsonStringValue() throws Exception {
+        ObjectMapper objectMapper = new ObjectMapper();
+
+        AppId appId = AppId.valueOf(APP_ID);
+
+        String serialized = objectMapper.writeValueAsString(appId);
+
+        //Without a fix fails on JDK17 with
+        //org.junit.ComparisonFailure:
+        //Expected :{"empty":false}
+        //Actual   :"3074457345618296002"
+        assertEquals(serialized, "\"" + APP_ID + "\"");
+    }
+
+    public static final class AppId implements CharSequence {
+
+        private final long value;
+
+        public AppId(long value) throws IllegalArgumentException {
+            this.value = value;
+        }
+
+        public static AppId valueOf(String value) throws IllegalArgumentException {
+            if (value == null) {
+                throw new IllegalArgumentException("value is null");
+            }
+            return new AppId(Long.parseLong(value));
+        }
+
+        @Override
+        public int length() {
+            return toString().length();
+        }
+
+        @Override
+        public char charAt(int index) {
+            return toString().charAt(index);
+        }
+
+        @Override
+        public CharSequence subSequence(int start, int end) {
+            return toString().subSequence(start, end);
+        }
+
+        // pay attention: no @JsonValue here
+        @Override
+        public String toString() {
+            return Long.toString(value);
+        }
+    }
+
+}