Fixed [JOHNZON-277]

Fails to deserialize inner empty JSON block {} at OBJECT_START

Signed-off-by: Markus KARG <markus@headcrashing.eu>

johnzon-jsonb/src/main/java/org/apache/johnzon/jsonb/serializer/JohnzonDeserializationContext.java

@@ -63,6 +63,8 @@ private JsonValue read(final JsonParser parser) {
                 parseObject(null, parser, objectBuilder);
                 return objectBuilder.build();
             }
+            case END_OBJECT:
+                return JsonValue.EMPTY_JSON_OBJECT;
             case START_ARRAY:
                 final JsonArrayBuilder arrayBuilder = builderFactory.createArrayBuilder();
                 parseArray(parser, arrayBuilder);

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

@@ -0,0 +1,83 @@
+/*
+ * 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 static org.junit.Assert.assertNotNull;
+
+import java.lang.reflect.Type;
+
+import javax.json.bind.Jsonb;
+import javax.json.bind.JsonbBuilder;
+import javax.json.bind.JsonbConfig;
+import javax.json.bind.serializer.DeserializationContext;
+import javax.json.bind.serializer.JsonbDeserializer;
+import javax.json.stream.JsonParser;
+
+import org.junit.Test;
+
+/**
+ * Tests compliance of {@link JohnzonDeserializationContext} with {@link DeserializationContext} wrt. empty inner JSON blocks.
+ *
+ * According to https://github.com/eclipse-ee4j/jsonb-api/blob/master/api/src/main/java/javax/json/bind/serializer/DeserializationContext.java#L34-L35 a
+ * deserialization context must be able to deserialize an object EVEN IN CASE the parser cursor is at {@code START_OBJECT}.
+ *
+ * Quote: "JsonParser cursor have to be at KEY_NAME before START_OBJECT / START_ARRAY, or at START_OBJECT / START_ARRAY 35 * to call this method."
+ *
+ * The latter case, "...or at START_OBJECT..." seems to fail in case the inner JSON to parse is an empty block "{}".
+ */
+public class DeserializationContextTest {
+
+    @Test
+    public void deserializeClass() throws Exception {
+        try (final Jsonb jsonb = JsonbBuilder.create()) {
+            // CAN create Bar instance from empty JSON inside of Foo => Parsing empty blocks seems to be allowed.
+            final Foo fooWithBar = jsonb.fromJson("{\"bar\":{}}", Foo.class);
+            assertNotNull(fooWithBar);
+            assertNotNull(fooWithBar.bar);
+        }
+
+        try (final Jsonb jsonb = JsonbBuilder.create(new JsonbConfig().withDeserializers(new CustomDeserializer()))) {
+            // CANNOT create Bar instance from empty JSON when parser cursor is at START_OBJECT => Bug in Johnzon
+            final Foo fooWithBar = jsonb.fromJson("{\"bar\":{}}", Foo.class); // throws exception "Unknown structure: END_OBJECT"
+            assertNotNull(fooWithBar);
+            assertNotNull(fooWithBar.bar);
+        }
+    }
+
+    public static class CustomDeserializer implements JsonbDeserializer<Foo> {
+        @Override
+        public Foo deserialize(final JsonParser parser, final DeserializationContext ctx, final Type rtType) {
+            parser.next(); // now cursor is at START_OBJECT of outer Foo, so let's create empty Foo...
+            final Foo foo = new Foo();
+            parser.next(); // now cursor is at KEY_NAME "bar"
+            parser.next(); // now cursor is at START_OBJECT of inner Bar, so let's fill Foo.bar...
+            foo.bar = ctx.deserialize(Bar.class, parser);
+            return foo;
+        }
+    }
+
+    public static class Foo {
+        public Bar bar;
+    }
+
+    public static class Bar {
+        // intentionally left blank
+    }
+
+}