JOHNZON-421 JsonbSerializer crashes when using primitives

If an object is serialised into a primitive, then we did crash with an Exception
JsonGenerationException: write(param) is only valid in arrays.

Author: struberg

johnzon-jsonb/src/test/java/org/apache/johnzon/jsonb/serializer/SerialiseAsPrimitiveTest.java

@@ -0,0 +1,129 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.johnzon.jsonb.serializer;
+
+import java.lang.reflect.Type;
+
+import org.junit.Test;
+
+import jakarta.json.bind.Jsonb;
+import jakarta.json.bind.JsonbBuilder;
+import jakarta.json.bind.annotation.JsonbTypeDeserializer;
+import jakarta.json.bind.annotation.JsonbTypeSerializer;
+import jakarta.json.bind.serializer.DeserializationContext;
+import jakarta.json.bind.serializer.JsonbDeserializer;
+import jakarta.json.bind.serializer.JsonbSerializer;
+import jakarta.json.bind.serializer.SerializationContext;
+import jakarta.json.stream.JsonGenerator;
+import jakarta.json.stream.JsonParser;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * This test checks a JsonbSerialize/JsonbDeserialize roundtrip when using a primitive as placeholder
+ */
+public class SerialiseAsPrimitiveTest {
+    
+    
+    public static class TestConstant {
+        public final static TestConstant VAL_1 = new TestConstant("A");
+        public final static TestConstant VAL_2 = new TestConstant("B");
+        public final static TestConstant VAL_3 = new TestConstant("C");
+
+        private final String code;
+
+        public TestConstant(String code) {
+            this.code = code;
+        }
+
+        public String getCode() {
+            return code;
+        }
+
+        public static TestConstant getByCode(String code) {
+            switch (code) {
+                case "A": return VAL_1;
+                case "B": return VAL_2;
+                case "C": return VAL_3;
+                default: return null;
+            }
+        }
+    }
+    
+    public static class ConstantUsage {
+        private int i;
+
+        @JsonbTypeSerializer(ConstantJsonbSerialiser.class)
+        @JsonbTypeDeserializer(ConstantJsonbDeserializer.class)
+        private TestConstant testConstant;
+
+        public int getI() {
+            return i;
+        }
+
+        public void setI(int i) {
+            this.i = i;
+        }
+
+        public TestConstant getTestConstant() {
+            return testConstant;
+        }
+
+        public void setTestConstant(TestConstant testEnum) {
+            this.testConstant = testEnum;
+        }
+    }
+
+    public static class ConstantJsonbSerialiser implements JsonbSerializer<TestConstant> {
+        @Override
+        public void serialize(TestConstant val, JsonGenerator generator, SerializationContext ctx) {
+            if (val == null) {
+                ctx.serialize(null, generator);
+            } else {
+                ctx.serialize(val.getCode(), generator);
+            }
+        }
+    }
+
+    public static class ConstantJsonbDeserializer implements JsonbDeserializer<TestConstant> {
+
+    @Override
+    public TestConstant deserialize(JsonParser parser, DeserializationContext ctx, Type rtType) {
+        if (rtType instanceof TestConstant) {
+            final String key = parser.getString();
+            if (key != null) {
+                return TestConstant.getByCode(key);
+            }
+        }
+        
+        return null;
+    }
+}
+
+
+
+    @Test
+    public void testEnumJsonb() {
+        ConstantUsage enumVerwender = new ConstantUsage();
+        enumVerwender.setI(1);
+        enumVerwender.setTestConstant(TestConstant.VAL_2);
+        
+        Jsonb jsonb = JsonbBuilder.create();
+        final String json = jsonb.toJson(enumVerwender);
+        assertTrue(json.contains("\"testConstant\":\"B\""));
+    }
+
+}

johnzon-mapper/src/main/java/org/apache/johnzon/mapper/MappingGeneratorImpl.java

@@ -131,7 +131,7 @@ public void doWriteObject(Object object, JsonGenerator generator, boolean writeB
                 return;
             }
 
-            if (writePrimitives(object)) {
+            if (writePrimitives(object, generator)) {
                 return;
             }
 
@@ -231,7 +231,8 @@ private JsonGenerator writeMapBody(final Map<?, ?> object, final Adapter itemCon
     /**
      * @return {@code true} if it was a primitive, {@code false} if the value did not get handled
      */
-    private boolean writePrimitives(final Object value) {
+    private boolean writePrimitives(final Object value,
+                                    final JsonGenerator generator) {
         boolean handled = false;
         if (value == null) {
             return true; // fake a write
@@ -550,7 +551,7 @@ private void writeIterator(final Adapter itemConverter, final String key,
             String valJsonPointer = jsonPointers == null ? null : jsonPointers.get(o);
             if (valJsonPointer != null) {
                 // write JsonPointer instead of the original object
-                writePrimitives(valJsonPointer);
+                writePrimitives(valJsonPointer, generator);
             } else {
                 ObjectConverter.Writer objectConverterToUse = objectConverter;
                 if (o != null && objectConverterToUse == null) {
@@ -693,7 +694,7 @@ private void writeArray(Class<?> type, Adapter itemConverter, String key, Object
     private void writeItem(final Object o, final Collection<String> ignoredProperties, JsonPointerTracker jsonPointer) {
         if (o == null) {
             generator.writeNull();
-        } else if (!writePrimitives(o)) {
+        } else if (!writePrimitives(o, generator)) {
             if (Collection.class.isInstance(o)) {
                 doWriteIterable(Collection.class.cast(o), ignoredProperties, jsonPointer);
             } else if (o.getClass().isArray()) {