Skipping over groovy metadata class + groovy test.

jr-objects/pom.xml

@@ -40,6 +40,12 @@ has no other dependencies, and provides additional builder-style content generat
       <artifactId>jackson-core</artifactId>
       <version>${jackson.version.core}</version>
     </dependency>
+    <dependency>
+      <groupId>org.codehaus.groovy</groupId>
+      <artifactId>groovy</artifactId>
+      <version>3.0.18</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>
@@ -64,9 +70,6 @@ has no other dependencies, and provides additional builder-style content generat
                 <goal>replace</goal>
             </goals>
             <phase>generate-sources</phase>
-<!--
-            <phase>process-sources</phase>
--->
           </execution>
         </executions>
           <configuration>

jr-objects/src/main/java/com/fasterxml/jackson/jr/ob/impl/BeanPropertyIntrospector.java

@@ -88,7 +88,7 @@ private POJODefinition _construct(Class<?> beanType, int features)
     private static void _introspect(Class<?> currType, Map<String, PropBuilder> props,
             int features)
     {
-        if (currType == null || currType == Object.class) {
+        if (currType == null || currType == Object.class || isGroovyMetaClass(currType)) {
             return;
         }
         // First, check base type
@@ -158,12 +158,7 @@ private static void _introspect(Class<?> currType, Map<String, PropBuilder> prop
     }
 
     private static PropBuilder _propFrom(Map<String,PropBuilder> props, String name) {
-        PropBuilder prop = props.get(name);
-        if (prop == null) {
-            prop = Prop.builder(name);
-            props.put(name, prop);
-        }
-        return prop;
+        return props.computeIfAbsent(name, Prop::builder);
     }
 
     private static String decap(String name) {
@@ -182,4 +177,13 @@ private static String decap(String name) {
         return name;
     }
 
+    /**
+     * Another helper method to deal with Groovy's problematic metadata accessors
+     *
+     * @implNote Groovy MetaClass have cyclic reference, and hence the class containing it should not be serialised without
+     * either removing that reference, or skipping over such references.
+     */
+    protected static boolean isGroovyMetaClass(Class<?> clazz) {
+        return clazz.getName().startsWith("groovy.lang");
+    }
 }

jr-objects/src/test/java/com/fasterxml/jackson/jr/GroovyTest.groovy

@@ -0,0 +1,21 @@
+package com.fasterxml.jackson.jr
+
+import com.fasterxml.jackson.jr.ob.JSON
+import com.fasterxml.jackson.jr.ob.TestBase
+
+class GroovyTest extends TestBase {
+
+    void testSimpleObject() throws Exception {
+        var data = JSON.std.asString(new MyClass())
+        var expected = "{\"aDouble\":0.0,\"aStr\":\"stringData\",\"anInt\":0,\"metaClass\":{}}";
+        assertEquals(data, expected)
+    }
+
+    private class MyClass {
+        public int anInt;                       //testing groovy primitive
+        public String aStr = "stringData";      //testing allocated object
+
+        public double aDouble;                  //
+        public Double aDoublesd;                //testing boxing object
+    }
+}