docs: Add package-level Javadoc for gateway core packages

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/discovery/package-info.java

@@ -15,9 +15,29 @@
  */
 
 /**
- * TODO: package javadoc.
+ * Service discovery integration for Spring Cloud Gateway.
+ *
+ * <p>
+ * This package provides support for dynamic route discovery using Spring Cloud's
+ * {@link org.springframework.cloud.client.discovery.DiscoveryClient}. It enables
+ * automatic route creation based on registered service instances in service registries
+ * such as Eureka, Consul, or Kubernetes.
+ * </p>
+ *
+ * <p>
+ * Key components:
+ * <ul>
+ * <li>{@link org.springframework.cloud.gateway.discovery.DiscoveryClientRouteDefinitionLocator}
+ * - Locates route definitions from discovered services</li>
+ * <li>{@link org.springframework.cloud.gateway.discovery.GatewayDiscoveryClientAutoConfiguration}
+ * - Auto-configuration for discovery client integration</li>
+ * </ul>
+ * </p>
+ *
+ * @see org.springframework.cloud.client.discovery.DiscoveryClient
+ * @see org.springframework.cloud.gateway.route.RouteDefinitionLocator
  */
 @NullMarked
 package org.springframework.cloud.gateway.discovery;
 
-import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.NullMarked;

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/event/package-info.java

@@ -15,9 +15,33 @@
  */
 
 /**
- * TODO: package javadoc.
+ * Event publishing and handling for Spring Cloud Gateway.
+ *
+ * <p>
+ * This package provides event-driven capabilities for gateway lifecycle and route
+ * management. It enables applications to react to gateway events such as route
+ * refreshes, route definitions being added or removed, and other gateway state changes.
+ * </p>
+ *
+ * <p>
+ * Key components:
+ * <ul>
+ * <li>Event classes for various gateway lifecycle events</li>
+ * <li>Event publishers for notifying listeners of gateway state changes</li>
+ * <li>Integration with Spring's event publishing mechanism</li>
+ * </ul>
+ * </p>
+ *
+ * <p>
+ * Applications can listen to these events by implementing
+ * {@link org.springframework.context.ApplicationListener} or using the
+ * {@link org.springframework.context.event.EventListener} annotation.
+ * </p>
+ *
+ * @see org.springframework.context.ApplicationEvent
+ * @see org.springframework.context.ApplicationListener
  */
 @NullMarked
 package org.springframework.cloud.gateway.event;
 
-import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.NullMarked;

spring-cloud-gateway-server-webflux/src/main/java/org/springframework/cloud/gateway/filter/package-info.java

@@ -9,15 +9,46 @@
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * WITHOUT WARRANTIES or conditions of ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 /**
- * TODO: package javadoc.
+ * Gateway filters for request and response processing.
+ *
+ * <p>
+ * This package contains the core filter implementations for Spring Cloud Gateway.
+ * Filters are used to modify incoming requests and outgoing responses as they pass
+ * through the gateway. They can be applied globally or scoped to specific routes.
+ * </p>
+ *
+ * <p>
+ * Filter types include:
+ * <ul>
+ * <li><strong>Global Filters:</strong> Applied to all routes</li>
+ * <li><strong>route Filters:</strong> Applied to specific routes</li>
+ * <li><strong>Pre-filters:</strong> Execute before the request is routed</li>
+ * <li><strong>Post-filters:</strong> Execute after the response is received</li>
+ * </ul>
+ * </p>
+ *
+ * <p>
+ * Common filter implementations:
+ * <ul>
+ * <li>{@link org.springframework.cloud.gateway.filter.NettyRoutingFilter}
+ * - Routes requests using Netty HTTP client</li>
+ * <li>{@link org.springframework.cloud.gateway.filter.ForwardRoutingFilter}
+ * - Forwards requests to local endpoints</li>
+ * <li>{@link org.springframework.cloud.gateway.filter.FunctionRoutingFilter}
+ * - Routes requests to Spring Cloud Function endpoints</li>
+ * </ul>
+ * </p>
+ *
+ * @see org.springframework.cloud.gateway.filter.GatewayFilter
+ * @see org.springframework.cloud.gateway.filter.GlobalFilter
  */
 @NullMarked
 package org.springframework.cloud.gateway.filter;
 
-import org.jspecify.annotations.NullMarked;
+import org.jspecify.annotations.NullMarked;