Extract generateListResultClass into ListResult (#2333)

#### What type of PR is this?

/kind improvement
/area core
/milestone 2.0
/release-note-none

#### What this PR does / why we need it:

Extract generateListResultClass into ListResult to make it easy to use in other places.

src/main/java/run/halo/app/extension/ListResult.java

@@ -7,6 +7,8 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import lombok.Data;
+import net.bytebuddy.ByteBuddy;
+import net.bytebuddy.description.type.TypeDescription;
 import org.springframework.data.util.Streamable;
 import org.springframework.util.Assert;
 
@@ -84,4 +86,23 @@ public class ListResult<T> implements Streamable<T> {
     public boolean isEmpty() {
         return Streamable.super.isEmpty();
     }
+
+    /**
+     * Generate generic ListResult class. Like {@code ListResult<User>}, {@code ListResult<Post>},
+     * etc.
+     *
+     * @param scheme scheme of the generic type.
+     * @return generic ListResult class.
+     */
+    public static Class<?> generateGenericClass(Scheme scheme) {
+        var generic =
+            TypeDescription.Generic.Builder.parameterizedType(ListResult.class, scheme.type())
+                .build();
+        return new ByteBuddy()
+            .subclass(generic)
+            .name(scheme.groupVersionKind().kind() + "List")
+            .make()
+            .load(ListResult.class.getClassLoader())
+            .getLoaded();
+    }
 }

src/main/java/run/halo/app/extension/router/ExtensionRouterFunctionFactory.java

@@ -5,8 +5,6 @@ import static org.springdoc.core.fn.builders.parameter.Builder.parameterBuilder;
 import static org.springdoc.core.fn.builders.requestbody.Builder.requestBodyBuilder;
 
 import io.swagger.v3.oas.annotations.enums.ParameterIn;
-import net.bytebuddy.ByteBuddy;
-import net.bytebuddy.description.type.TypeDescription;
 import org.springdoc.webflux.core.fn.SpringdocRouteBuilder;
 import org.springframework.lang.NonNull;
 import org.springframework.web.reactive.function.server.HandlerFunction;
@@ -55,7 +53,7 @@ public class ExtensionRouterFunctionFactory {
                         .tag(tagName)
                         .response(responseBuilder().responseCode("200")
                             .description("Response " + scheme.plural())
-                            .implementation(generateListResultClass()));
+                            .implementation(ListResult.generateGenericClass(scheme)));
                     QueryParamBuildUtil.buildParametersFromType(builder, ListRequest.class);
                 })
             .POST(createHandler.pathPattern(), createHandler,
@@ -130,15 +128,4 @@ public class ExtensionRouterFunctionFactory {
 
     }
 
-    private Class<?> generateListResultClass() {
-        var generic =
-            TypeDescription.Generic.Builder.parameterizedType(ListResult.class, scheme.type())
-                .build();
-        return new ByteBuddy()
-            .subclass(generic)
-            .name(scheme.groupVersionKind().kind() + "List")
-            .make()
-            .load(this.getClass().getClassLoader())
-            .getLoaded();
-    }
 }

src/test/java/run/halo/app/extension/ListResultTest.java

@@ -0,0 +1,22 @@
+package run.halo.app.extension;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.lang.reflect.ParameterizedType;
+import org.junit.jupiter.api.Test;
+
+class ListResultTest {
+
+    @Test
+    void generateGenericClass() {
+        var fakeListClass =
+            ListResult.generateGenericClass(Scheme.buildFromType(FakeExtension.class));
+        assertTrue(ListResult.class.isAssignableFrom(fakeListClass));
+        assertSame(FakeExtension.class, ((ParameterizedType) fakeListClass.getGenericSuperclass())
+            .getActualTypeArguments()[0]);
+        assertEquals("FakeList", fakeListClass.getSimpleName());
+    }
+
+}