Add day of month to day of week, X#Y syntax

.sdkmanrc

@@ -0,0 +1,3 @@
+# Enable auto-env through the sdkman_auto_env config
+# Add key=value pairs of SDKs to use below
+java=8.0.412-zulu

src/main/java/com/cronutils/mapper/CronMapper.java

@@ -29,7 +29,6 @@
 import com.cronutils.model.field.definition.FieldDefinition;
 import com.cronutils.model.field.expression.*;
 import com.cronutils.model.field.expression.visitor.FieldExpressionVisitorAdaptor;
-import com.cronutils.model.field.expression.visitor.ValueMappingFieldExpressionVisitor;
 import com.cronutils.model.field.value.FieldValue;
 import com.cronutils.model.field.value.IntegerFieldValue;
 import com.cronutils.model.field.value.SpecialChar;
@@ -286,12 +285,14 @@ static Function<CronField, CronField> dayOfWeekMapping(final DayOfWeekFieldDefin
             final FieldExpression expression = field.getExpression();
             FieldExpression dest = null;
             dest = expression.accept(new FieldExpressionVisitorAdaptor() {
+                @Override
                 public FieldExpression visit(Every every) {
                     return new Every(every.getExpression().accept(this), every.getPeriod());
                 }
 
+                @Override
                 public FieldExpression visit(On on) {
-                    return new On(mapDayOfWeek(sourceDef, targetDef, on.getTime()), on.getSpecialChar());
+                    return new On(mapDayOfWeek(sourceDef, targetDef, on.getTime()), on.getSpecialChar(),  on.getNth());
                 }
 
                 @Override

src/test/java/com/cronutils/Issue605Test.java

@@ -0,0 +1,44 @@
+package com.cronutils;
+
+import com.cronutils.mapper.CronMapper;
+import com.cronutils.model.Cron;
+import com.cronutils.model.CronType;
+import com.cronutils.model.definition.CronDefinition;
+import com.cronutils.model.definition.CronDefinitionBuilder;
+import com.cronutils.parser.CronParser;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.stream.Stream;
+
+import static com.cronutils.model.CronType.QUARTZ;
+import static com.cronutils.model.CronType.SPRING;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class Issue605Test {
+
+    static Stream<Arguments> cronExpressions() {
+        return Stream.of(
+                Arguments.of(QUARTZ, CronMapper.fromQuartzToCron4j(), "0 0 * * 4#1"),
+                Arguments.of(QUARTZ, CronMapper.fromQuartzToSpring(), "0 0 0 ? * 4#1"),
+                Arguments.of(QUARTZ, CronMapper.fromQuartzToUnix(), "0 0 * * 4#1"),
+                Arguments.of(SPRING, CronMapper.fromSpringToQuartz(), "0 0 0 ? * 6#1 *")
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("cronExpressions")
+    void testDayOfWeekMappingSpring(CronType cronType, CronMapper mapper, String expectedExpression) {
+        Cron sourceCron = getCron(cronType, "0 0 0 ? * 5#1");
+        Cron destinationCron = mapper.map(sourceCron);
+        assertEquals(expectedExpression, destinationCron.asString());
+    }
+
+    private Cron getCron(CronType cronType, @SuppressWarnings("SameParameterValue") final String quartzExpression) {
+        final CronDefinition cronDefinition = CronDefinitionBuilder.instanceDefinitionFor(cronType);
+        final CronParser parser = new CronParser(cronDefinition);
+        return parser.parse(quartzExpression);
+    }
+
+}