Fix #4082: add check for attempts to ser/deser Java 8 optionals witho…

…ut module

release-notes/VERSION-2.x

@@ -63,6 +63,8 @@ Project: jackson-databind
 #4078: `java.desktop` module is no longer optional
  (reported by Andreas Z)
  (fix contributed by Joo-Hyuk K)
+#4082: `ClassUtil` fails with `java.lang.reflect.InaccessibleObjectException`
+  trying to setAccessible on `OptionalInt` with JDK 17+
 
 2.15.3 (not yet released)
 

src/main/java/com/fasterxml/jackson/databind/util/BeanUtil.java

@@ -309,6 +309,9 @@ public static String checkUnsupportedType(JavaType type) {
         } else if (isJodaTimeClass(className)) {
             typeName =  "Joda date/time";
             moduleName = "com.fasterxml.jackson.datatype:jackson-datatype-joda";
+        } else if (isJava8OptionalClass(className)) {
+            typeName =  "Java 8 optional";
+            moduleName = "com.fasterxml.jackson.datatype:jackson-datatype-jdk8";
         } else {
             return null;
         }
@@ -323,17 +326,31 @@ public static boolean isJava8TimeClass(Class<?> rawType) {
         return isJava8TimeClass(rawType.getName());
     }
 
+    // @since 2.12
     private static boolean isJava8TimeClass(String className) {
         return className.startsWith("java.time.");
     }
 
+    /**
+     * @since 2.16
+     */
+    public static boolean isJava8OptionalClass(Class<?> rawType) {
+        return isJava8OptionalClass(rawType.getName());
+    }
+
+    // @since 2.16
+    private static boolean isJava8OptionalClass(String className) {
+        return className.startsWith("java.util.Optional");
+    }
+
     /**
      * @since 2.12
      */
     public static boolean isJodaTimeClass(Class<?> rawType) {
         return isJodaTimeClass(rawType.getName());
     }
 
+    // @since 2.12
     private static boolean isJodaTimeClass(String className) {
         return className.startsWith("org.joda.time.");
     }

src/test/java/com/fasterxml/jackson/databind/interop/OptionalJava8Fallbacks4082Test.java

@@ -0,0 +1,89 @@
+package com.fasterxml.jackson.databind.interop;
+
+import java.util.Optional;
+import java.util.OptionalDouble;
+import java.util.OptionalInt;
+import java.util.OptionalLong;
+
+import com.fasterxml.jackson.core.*;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
+import com.fasterxml.jackson.databind.util.TokenBuffer;
+
+// [databind#4082]: add fallback handling for Java 8 Optional types, to
+// prevent accidental serialization as POJOs, as well as give more information
+// on deserialization attempts
+//
+// @since 2.16
+public class OptionalJava8Fallbacks4082Test extends BaseMapTest
+{
+    private final ObjectMapper MAPPER = newJsonMapper();
+
+    // Test to prevent serialization as POJO, without Java 8 date/time module:
+    public void testPreventSerialization() throws Exception {
+        _testPreventSerialization(Optional.empty());
+        _testPreventSerialization(OptionalInt.of(13));
+        _testPreventSerialization(OptionalLong.of(-1L));
+        _testPreventSerialization(OptionalDouble.of(0.5));
+    }
+
+    private void _testPreventSerialization(Object value) throws Exception
+    {
+        try {
+            String json = MAPPER.writeValueAsString(value);
+            fail("Should not pass, wrote out as\n: "+json);
+        } catch (InvalidDefinitionException e) {
+            verifyException(e, "Java 8 optional type `"+value.getClass().getName()
+                    +"` not supported by default");
+            verifyException(e, "add Module \"com.fasterxml.jackson.datatype:jackson-datatype-jdk8\"");
+        }
+    }
+
+    public void testBetterDeserializationError() throws Exception
+    {
+        _testBetterDeserializationError(Optional.class);
+        _testBetterDeserializationError(OptionalInt.class);
+        _testBetterDeserializationError(OptionalLong.class);
+        _testBetterDeserializationError(OptionalDouble.class);
+    }
+
+    private void _testBetterDeserializationError(Class<?> target) throws Exception
+    {
+        try {
+            Object result = MAPPER.readValue(" 0 ", target);
+            fail("Not expecting to pass, resulted in: "+result);
+        } catch (InvalidDefinitionException e) {
+            verifyException(e, "Java 8 optional type `"+target.getName()+"` not supported by default");
+            verifyException(e, "add Module \"com.fasterxml.jackson.datatype:jackson-datatype-jdk8\"");
+        }
+    }
+
+    // But, [databind#3091], allow deser from JsonToken.VALUE_EMBEDDED_OBJECT
+    public void testAllowAsEmbedded() throws Exception
+    {
+        Optional<Object> optValue = Optional.empty();
+        try (TokenBuffer tb = new TokenBuffer((ObjectCodec) null, false)) {
+            tb.writeEmbeddedObject(optValue);
+
+            try (JsonParser p = tb.asParser()) {
+                Optional<?>  result = MAPPER.readValue(p, Optional.class);
+                assertSame(optValue, result);
+            }
+        }
+
+        // but also try deser into an array
+        try (TokenBuffer tb = new TokenBuffer((ObjectCodec) null, false)) {
+            tb.writeStartArray();
+            tb.writeEmbeddedObject(optValue);
+            tb.writeEndArray();
+
+            try (JsonParser p = tb.asParser()) {
+                Object[] result = MAPPER.readValue(p, Object[].class);
+                assertNotNull(result);
+                assertEquals(1, result.length);
+                assertSame(optValue, result[0]);
+            }
+        }
+    }
+}