refactor: GH-3998 Refactor org.springframework.ai.ollama.OllamaChatModel#ollamaChatRequest to support custom implementations of AbstractMessage and align with other ChatModel implementations.

Signed-off-by: Sun Yuhan <sunyuhan1998@users.noreply.github.com>

Author: sunyuhan1998

models/spring-ai-ollama/src/main/java/org/springframework/ai/ollama/OllamaChatModel.java

@@ -32,7 +32,7 @@
 import reactor.core.scheduler.Schedulers;
 
 import org.springframework.ai.chat.messages.AssistantMessage;
-import org.springframework.ai.chat.messages.SystemMessage;
+import org.springframework.ai.chat.messages.MessageType;
 import org.springframework.ai.chat.messages.ToolResponseMessage;
 import org.springframework.ai.chat.messages.UserMessage;
 import org.springframework.ai.chat.metadata.ChatGenerationMetadata;
@@ -439,18 +439,21 @@ Prompt buildRequestPrompt(Prompt prompt) {
 OllamaApi.ChatRequest ollamaChatRequest(Prompt prompt, boolean stream) {
 
 List<OllamaApi.Message> ollamaMessages = prompt.getInstructions().stream().map(message -> {
-if (message instanceof UserMessage userMessage) {
+if (message.getMessageType() == MessageType.USER || message.getMessageType() == MessageType.SYSTEM) {
 var messageBuilder = OllamaApi.Message.builder(Role.USER).content(message.getText());
-if (!CollectionUtils.isEmpty(userMessage.getMedia())) {
-messageBuilder.images(
-userMessage.getMedia().stream().map(media -> this.fromMediaData(media.getData())).toList());
+if (message instanceof UserMessage userMessage) {
+if (!CollectionUtils.isEmpty(userMessage.getMedia())) {
+messageBuilder.images(userMessage.getMedia()
+.stream()
+.map(media -> this.fromMediaData(media.getData()))
+.toList());
+}
 }
+
 return List.of(messageBuilder.build());
 }
-else if (message instanceof SystemMessage systemMessage) {
-return List.of(OllamaApi.Message.builder(Role.SYSTEM).content(systemMessage.getText()).build());
-}
-else if (message instanceof AssistantMessage assistantMessage) {
+else if (message.getMessageType() == MessageType.ASSISTANT) {
+var assistantMessage = (AssistantMessage) message;
 List<ToolCall> toolCalls = null;
 if (!CollectionUtils.isEmpty(assistantMessage.getToolCalls())) {
 toolCalls = assistantMessage.getToolCalls().stream().map(toolCall -> {
@@ -465,7 +468,8 @@ else if (message instanceof AssistantMessage assistantMessage) {
 .toolCalls(toolCalls)
 .build());
 }
-else if (message instanceof ToolResponseMessage toolMessage) {
+else if (message.getMessageType() == MessageType.TOOL) {
+ToolResponseMessage toolMessage = (ToolResponseMessage) message;
 return toolMessage.getResponses()
 .stream()
 .map(tr -> OllamaApi.Message.builder(Role.TOOL).content(tr.responseData()).build())