implement issue #6168 configure jackson 3 mapper

vertx-core/src/main/java21/io/vertx/core/json/jackson/v3/DatabindCodec.java

@@ -17,6 +17,7 @@
 import tools.jackson.core.StreamWriteFeature;
 import tools.jackson.core.type.TypeReference;
 import tools.jackson.databind.ObjectMapper;
+import tools.jackson.databind.cfg.MapperBuilder;
 import tools.jackson.databind.json.JsonMapper;
 import io.netty.buffer.ByteBufInputStream;
 import io.vertx.core.buffer.Buffer;
@@ -26,20 +27,20 @@
 import io.vertx.core.json.JsonArray;
 import io.vertx.core.json.JsonObject;
 
-import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.Reader;
 import java.io.Writer;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Function;
 
 /**
  * @author <a href="mailto:julien@julienviet.com">Julien Viet</a>
  */
 public class DatabindCodec extends JacksonCodec {
 
-  private static final ObjectMapper mapper = JsonMapper
+  private static volatile ObjectMapper mapper = JsonMapper
     .builder(JacksonCodec.factory)
     .addModule(new VertxModule())
     .build();
@@ -51,6 +52,16 @@ public static ObjectMapper mapper() {
     return mapper;
   }
 
+  /**
+   * this creates a @{@link MapperBuilder} from the already configured @{@link ObjectMapper}
+   * this builder is passed to the function which returns a new mapper
+   *
+   * @param f update mapper function
+   */
+  public static void rebuildMapper(Function<MapperBuilder<ObjectMapper, ?>, ObjectMapper> f) {
+    mapper = f.apply(mapper().rebuild());
+  }
+
   @Override
   public <T> T fromValue(Object json, Class<T> clazz) {
     T value = DatabindCodec.mapper.convertValue(json, clazz);

vertx-core/src/test/java/io/vertx/tests/json/jackson/v3/MapperConfigurationTest.java

@@ -0,0 +1,35 @@
+package io.vertx.tests.json.jackson.v3;
+
+import io.vertx.core.json.jackson.v3.DatabindCodec;
+import org.junit.Test;
+import tools.jackson.core.JacksonException;
+import tools.jackson.databind.DeserializationFeature;
+import tools.jackson.databind.ObjectMapper;
+
+import static org.junit.Assert.assertThrows;
+
+public class MapperConfigurationTest {
+
+  public static class User {
+    private int age;
+
+    public int getAge() {
+      return age;
+    }
+
+    public void setAge(int age) {
+      this.age = age;
+    }
+  }
+
+  @Test
+  public void testConfigurationChanges() {
+    final ObjectMapper oldMapper = DatabindCodec.mapper();
+    assertThrows(JacksonException.class, () -> oldMapper.readValue("{\"age\": null}", User.class));
+
+    DatabindCodec.rebuildMapper(builder -> builder.disable(DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES).build());
+
+    final ObjectMapper newMapper = DatabindCodec.mapper();
+    newMapper.readValue("{\"age\": null}", User.class);
+  }
+}