DATACMNS-1373 - Use ReflectUtils.defineClass(…) to load generated EntityInstantiators.

We now use Spring's ReflectUtils.defineClass(…) to load generated EntityInstantiators which uses internally either MethodHandles.Lookup.defineClass(…) (on Java 9 and higher) or reflective defineClass invocation on the originating ClassLoader. Class injection into the originating ClassLoader assigns the ClassLoader of the entity to the generated class which allows optimized instantiation of package-protected classes and constructors.

Original pull request: #308.

src/test/java/org/springframework/data/convert/ClassGeneratingEntityInstantiatorUnitTests.java

@@ -303,6 +303,66 @@ public class ClassGeneratingEntityInstantiatorUnitTests<P extends PersistentProp
 		});
 	}
 
+	@Test // DATACMNS-1373
+	public void shouldInstantiateProtectedInnerClass() {
+
+		prepareMocks(ProtectedInnerClass.class);
+
+		assertThat(this.instance.shouldUseReflectionEntityInstantiator(entity)).isFalse();
+		assertThat(this.instance.createInstance(entity, provider)).isInstanceOf(ProtectedInnerClass.class);
+	}
+
+	@Test // DATACMNS-1373
+	public void shouldInstantiatePackagePrivateInnerClass() {
+
+		prepareMocks(PackagePrivateInnerClass.class);
+
+		assertThat(this.instance.shouldUseReflectionEntityInstantiator(entity)).isFalse();
+		assertThat(this.instance.createInstance(entity, provider)).isInstanceOf(PackagePrivateInnerClass.class);
+	}
+
+	@Test // DATACMNS-1373
+	public void shouldNotInstantiatePrivateInnerClass() {
+
+		prepareMocks(PrivateInnerClass.class);
+
+		assertThat(this.instance.shouldUseReflectionEntityInstantiator(entity)).isTrue();
+	}
+
+	@Test // DATACMNS-1373
+	public void shouldInstantiateClassWithPackagePrivateConstructor() {
+
+		prepareMocks(ClassWithPackagePrivateConstructor.class);
+
+		assertThat(this.instance.shouldUseReflectionEntityInstantiator(entity)).isFalse();
+		assertThat(this.instance.createInstance(entity, provider)).isInstanceOf(ClassWithPackagePrivateConstructor.class);
+	}
+
+	@Test // DATACMNS-1373
+	public void shouldInstantiateClassInDefaultPackage() throws ClassNotFoundException {
+
+		Class<?> typeInDefaultPackage = Class.forName("TypeInDefaultPackage");
+		prepareMocks(typeInDefaultPackage);
+
+		assertThat(this.instance.shouldUseReflectionEntityInstantiator(entity)).isFalse();
+		assertThat(this.instance.createInstance(entity, provider)).isInstanceOf(typeInDefaultPackage);
+	}
+
+	@Test // DATACMNS-1373
+	public void shouldNotInstantiateClassWithPrivateConstructor() {
+
+		prepareMocks(ClassWithPrivateConstructor.class);
+
+		assertThat(this.instance.shouldUseReflectionEntityInstantiator(entity)).isTrue();
+	}
+
+	private void prepareMocks(Class<?> type) {
+
+		doReturn(type).when(entity).getType();
+		doReturn(PreferredConstructorDiscoverer.discover(type))//
+				.when(entity).getPersistenceConstructor();
+	}
+
 	static class Foo {
 
 		Foo(String foo) {
@@ -424,4 +484,21 @@ public class ClassGeneratingEntityInstantiatorUnitTests<P extends PersistentProp
 			this.param7 = param7;
 		}
 	}
+
+	protected static class ProtectedInnerClass {}
+
+	static class PackagePrivateInnerClass {}
+
+	private static class PrivateInnerClass {}
+
+	static class ClassWithPrivateConstructor {
+
+		private ClassWithPrivateConstructor() {}
+	}
+
+	static class ClassWithPackagePrivateConstructor {
+
+		ClassWithPackagePrivateConstructor() {}
+	}
+
 }