mybatis/mybatis-3 · error · ExecutorException

Error instantiating collection property for result '{}'. Ca

Error message

Error instantiating collection property for result '{}'.  Cause: {}

What it means

MyBatis tried to lazily instantiate a collection property for a nested result (the property was null and its declared Java type is a collection) and the objectFactory.create(type) call threw — typically InstantiationException/AccessException because the collection type is abstract or has no no-arg constructor. The wrap names the resultMapping property and keeps the cause.

Source

Thrown at src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java:1645

    return list.isEmpty() ? null : list.get(0);
  }

  private Object instantiateCollectionPropertyIfAppropriate(ResultMapping resultMapping, MetaObject metaObject) {
    final String propertyName = resultMapping.getProperty();
    Object propertyValue = metaObject.getValue(propertyName);
    if (propertyValue == null) {
      Class<?> type = resultMapping.getJavaType();
      if (type == null) {
        type = metaObject.getSetterType(propertyName);
      }
      try {
        if (objectFactory.isCollection(type)) {
          propertyValue = objectFactory.create(type);
          metaObject.setValue(propertyName, propertyValue);
          return propertyValue;
        }
      } catch (Exception e) {
        throw new ExecutorException(
            "Error instantiating collection property for result '" + resultMapping.getProperty() + "'.  Cause: " + e,
            e);
      }
    } else if (objectFactory.isCollection(propertyValue.getClass())) {
      return propertyValue;
    }
    return null;
  }

  private boolean hasTypeHandlerForResultObject(ResultSetWrapper rsw, Class<?> resultType) {
    if (rsw.getColumnNames().size() == 1) {
      return typeHandlerRegistry.hasTypeHandler(resultType, rsw.getJdbcType(rsw.getColumnNames().get(0)));
    }
    return typeHandlerRegistry.hasTypeHandler(resultType);
  }

}

View on GitHub (pinned to 008069adb1)

Solutions

1. Use a concrete collection type for the property/mapping javaType (java.util.ArrayList, java.util.LinkedHashSet, etc.).
2. If the property's declared setter type is already concrete, remove the explicit javaType so MyBatis derives it from the setter.
3. Give custom collection classes a public no-arg constructor, or configure an ObjectFactory that knows how to build them.
4. Register a custom DefaultObjectFactory that handles your collection types.

Example fix

<!-- before -->
<collection property="items" ofType="Item" javaType="java.util.List"/>

<!-- after -->
<collection property="items" ofType="Item" javaType="java.util.ArrayList"/>
<!-- or simply omit javaType if the setter type is concrete -->

// assert the nested collection property type is instantiable before first use
Class<?> t = resultMapping.getJavaType() != null
    ? resultMapping.getJavaType()
    : metaObject.getSetterType(propertyName);
if (objectFactory.isCollection(t) && (Modifier.isAbstract(t.getModifiers())
    || Arrays.stream(t.getConstructors()).noneMatch(c -> c.getParameterCount() == 0))) {
  throw new IllegalStateException(t + " is a collection without a public no-arg constructor;");
}

static boolean instantiableCollection(Class<?> c) {
  return Collection.class.isAssignableFrom(c)
      && !Modifier.isAbstract(c.getModifiers())
      && Arrays.stream(c.getConstructors()).anyMatch(x -> x.getParameterCount() == 0);
}

When it happens

Trigger: A nested collection mapping whose javaType is a non-instantiable collection (e.g. java.util.List, java.util.Collection, java.util.Set interfaces directly, or a custom collection lacking a public no-arg constructor); instantiateCollectionPropertyIfAppropriate runs before linking nested rows and object creation fails.

Common situations: Declaring javaType="java.util.List" instead of a concrete class on <collection>; custom ImmutableBag collection types; a custom ObjectFactory that rejects or fails to create collection classes; mapping onto a collection whose constructor requires arguments.

Related errors

• Do not know how to create an instance of " + resultType
• Cannot add a collection result to non-collection based resul
• Error instantiating {} with invalid types ({}) or values ({}
• Error creating instance. Cause: {cause}
• Could not find a parent resultMap with id '{extend}'

AI-assisted analysis of mybatis/mybatis-3@008069adb1 (2026-08-14). Data as JSON: /api/errors/1213466b0f77e3df. Report an issue: GitHub.