fix: initial state for session creation

dev/src/main/java/com/google/adk/web/controller/SessionController.java

@@ -21,6 +21,7 @@
 import com.google.adk.sessions.BaseSessionService;
 import com.google.adk.sessions.ListSessionsResponse;
 import com.google.adk.sessions.Session;
+import com.google.adk.web.dto.SessionRequest;
 import io.reactivex.rxjava3.core.Maybe;
 import io.reactivex.rxjava3.core.Single;
 import java.util.Collections;
@@ -167,13 +168,15 @@ public Session createSessionWithId(
       @PathVariable String appName,
       @PathVariable String userId,
       @PathVariable String sessionId,
-      @RequestBody(required = false) Map<String, Object> state) {
+      @RequestBody(required = false) SessionRequest body) {
     log.info(
-        "Request received for POST /apps/{}/users/{}/sessions/{} with state: {}",
+        "Request received for POST /apps/{}/users/{}/sessions/{} with request body: {}",
         appName,
         userId,
         sessionId,
-        state);
+        body);
+
+    Map<String, Object> initialState = (body != null) ? body.getState() : Collections.emptyMap();
 
     try {
       findSessionOrThrow(appName, userId, sessionId);
@@ -190,7 +193,6 @@ public Session createSessionWithId(
       log.info("Session {} not found, proceeding with creation.", sessionId);
     }
 
-    Map<String, Object> initialState = (state != null) ? state : Collections.emptyMap();
     try {
       Session createdSession =
           sessionService
@@ -228,18 +230,17 @@ public Session createSessionWithId(
   public Session createSession(
       @PathVariable String appName,
       @PathVariable String userId,
-      @RequestBody(required = false) Map<String, Object> state) {
+      @RequestBody(required = false) SessionRequest body) {
 
     log.info(
-        "Request received for POST /apps/{}/users/{}/sessions (service generates ID) with state:"
-            + " {}",
+        "Request received for POST /apps/{}/users/{}/sessions (service generates ID) with request"
+            + " body: {}",
         appName,
         userId,
-        state);
+        body);
 
-    Map<String, Object> initialState = (state != null) ? state : Collections.emptyMap();
     try {
-
+      Map<String, Object> initialState = (body != null) ? body.getState() : Collections.emptyMap();
       Session createdSession =
           sessionService
               .createSession(appName, userId, new ConcurrentHashMap<>(initialState), null)

dev/src/main/java/com/google/adk/web/dto/SessionRequest.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * 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.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.adk.web.dto;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.google.common.collect.ImmutableMap;
+import java.util.Map;
+
+/**
+ * Data Transfer Object (DTO) for POST /apps/{appName}/users/{userId}/sessions and POST
+ * /apps/{appName}/users/{userId}/sessions/{sessionId} equests. Contains information for a session.
+ */
+public final class SessionRequest {
+  private final ImmutableMap<String, Object> state;
+
+  @JsonCreator
+  public SessionRequest(@JsonProperty("state") Map<String, Object> state) {
+    this.state = (state == null) ? ImmutableMap.of() : ImmutableMap.copyOf(state);
+  }
+
+  public ImmutableMap<String, Object> getState() {
+    return state;
+  }
+}