Solve the problem of occasional incomplete response content. (langcha…

…in4j#699)

It is now possible for Qwen models to return messages with content when
finishReason == STOP (but not always). compatible with this situation.

When finishReason != STOP, if the returned message has no content,
NullPointerException will still be thrown.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit


- **New Features**
- Enhanced conversation handling in the application with new methods for
checking and extracting answers.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

langchain4j-dashscope/src/main/java/dev/langchain4j/model/dashscope/QwenHelper.java

@@ -163,6 +163,14 @@ static String roleFrom(ChatMessage message) {
         }
     }
 
+    static boolean hasAnswer(GenerationResult result) {
+        return Optional.of(result)
+                .map(GenerationResult::getOutput)
+                .map(GenerationOutput::getChoices)
+                .filter(choices -> !choices.isEmpty())
+                .isPresent();
+    }
+
     static String answerFrom(GenerationResult result) {
         return Optional.of(result)
                 .map(GenerationResult::getOutput)
@@ -178,6 +186,18 @@ static String answerFrom(GenerationResult result) {
                         .orElseThrow(NullPointerException::new));
     }
 
+    static boolean hasAnswer(MultiModalConversationResult result) {
+        return Optional.of(result)
+                .map(MultiModalConversationResult::getOutput)
+                .map(MultiModalConversationOutput::getChoices)
+                .filter(choices -> !choices.isEmpty())
+                .map(choices -> choices.get(0))
+                .map(MultiModalConversationOutput.Choice::getMessage)
+                .map(MultiModalMessage::getContent)
+                .filter(contents -> !contents.isEmpty())
+                .isPresent();
+    }
+
     static String answerFrom(MultiModalConversationResult result) {
         return Optional.of(result)
                 .map(MultiModalConversationResult::getOutput)

langchain4j-dashscope/src/main/java/dev/langchain4j/model/dashscope/QwenStreamingResponseBuilder.java

@@ -9,8 +9,7 @@
 import dev.langchain4j.model.output.Response;
 import dev.langchain4j.model.output.TokenUsage;
 
-import static dev.langchain4j.model.dashscope.QwenHelper.answerFrom;
-import static dev.langchain4j.model.dashscope.QwenHelper.finishReasonFrom;
+import static dev.langchain4j.model.dashscope.QwenHelper.*;
 
 public class QwenStreamingResponseBuilder {
     private final StringBuilder generatedContent = new StringBuilder();
@@ -37,7 +36,9 @@ public String append(GenerationResult partialResponse) {
         FinishReason finishReason = finishReasonFrom(partialResponse);
         if (finishReason != null) {
             this.finishReason = finishReason;
-            return null;
+            if (!hasAnswer(partialResponse)) {
+                return null;
+            }
         }
 
         String partialContent = answerFrom(partialResponse);
@@ -60,7 +61,9 @@ public String append(MultiModalConversationResult partialResponse) {
         FinishReason finishReason = finishReasonFrom(partialResponse);
         if (finishReason != null) {
             this.finishReason = finishReason;
-            return null;
+            if (!hasAnswer(partialResponse)) {
+                return null;
+            }
         }
 
         String partialContent = answerFrom(partialResponse);

langchain4j-dashscope/src/test/java/dev/langchain4j/model/dashscope/QwenStreamingChatModelIT.java

@@ -27,6 +27,7 @@ public void should_send_non_multimodal_messages_and_receive_response(String mode
         System.out.println(response);
 
         assertThat(response.content().text()).containsIgnoringCase("rain");
+        assertThat(response.content().text()).endsWith("That's all!");
     }
 
     @ParameterizedTest
@@ -42,6 +43,7 @@ public void should_send_multimodal_image_url_and_receive_response(String modelNa
         System.out.println(response);
 
         assertThat(response.content().text()).containsIgnoringCase("dog");
+        assertThat(response.content().text()).endsWith("That's all!");
     }
 
     @ParameterizedTest
@@ -57,5 +59,6 @@ public void should_send_multimodal_image_data_and_receive_response(String modelN
         System.out.println(response);
 
         assertThat(response.content().text()).containsIgnoringCase("parrot");
+        assertThat(response.content().text()).endsWith("That's all!");
     }
 }

langchain4j-dashscope/src/test/java/dev/langchain4j/model/dashscope/QwenTestHelper.java

@@ -20,18 +20,14 @@ public class QwenTestHelper {
     public static Stream<Arguments> languageModelNameProvider() {
         return Stream.of(
                 Arguments.of(QwenModelName.QWEN_TURBO),
-                Arguments.of(QwenModelName.QWEN_PLUS),
-                Arguments.of(QwenModelName.QWEN_7B_CHAT),
-                Arguments.of(QwenModelName.QWEN_14B_CHAT)
+                Arguments.of(QwenModelName.QWEN_PLUS)
         );
     }
 
     public static Stream<Arguments> nonMultimodalChatModelNameProvider() {
         return Stream.of(
                 Arguments.of(QwenModelName.QWEN_TURBO),
-                Arguments.of(QwenModelName.QWEN_PLUS),
-                Arguments.of(QwenModelName.QWEN_7B_CHAT),
-                Arguments.of(QwenModelName.QWEN_14B_CHAT)
+                Arguments.of(QwenModelName.QWEN_PLUS)
         );
     }
 
@@ -57,9 +53,10 @@ public static List<ChatMessage> chatMessages() {
         List<ChatMessage> messages = new LinkedList<>();
         messages.add(SystemMessage.from("Your name is Jack." +
                 " You like to answer other people's questions briefly." +
-                " It's rainy today."));
+                " It's rainy today." +
+                " When you're done, end with \"That's all!\"."));
         messages.add(UserMessage.from("Hello. What's your name?"));
-        messages.add(AiMessage.from("Jack."));
+        messages.add(AiMessage.from("Jack. That's all!"));
         messages.add(UserMessage.from("How about the weather today?"));
         return messages;
     }
@@ -69,7 +66,7 @@ public static List<ChatMessage> multimodalChatMessagesWithImageUrl() {
                 .url("https://dashscope.oss-cn-beijing.aliyuncs.com/images/dog_and_girl.jpeg")
                 .build();
         ImageContent imageContent = ImageContent.from(image);
-        TextContent textContent = TextContent.from("What animal is in the picture?");
+        TextContent textContent = TextContent.from("What animal is in the picture? When you're done, end with \"That's all!\".");
         return Collections.singletonList(UserMessage.from(imageContent, textContent));
     }
 
@@ -78,7 +75,7 @@ public static List<ChatMessage> multimodalChatMessagesWithImageData() {
                 .base64Data(multimodalImageData())
                 .build();
         ImageContent imageContent = ImageContent.from(image);
-        TextContent textContent = TextContent.from("What animal is in the picture?");
+        TextContent textContent = TextContent.from("What animal is in the picture? When you're done, end with \"That's all!\".");
         return Collections.singletonList(UserMessage.from(imageContent, textContent));
     }