如何在LangChain中实现流式输出？有什么应用场景

publicclassCustomStreamingHandlerextendsBaseCallbackHandler{
    @Override
    publicvoidonLlmNewToken(String token){
        // 每个新token都会触发这个方法
        System.out.print(token);
        // 也可以发送到WebSocket、更新数据库等
    }

    @Override
    publicvoidonLlmEnd(LlmResult result){
    // 发送结束标记
    System.out.println("\n[生成完成]");
}

@Override
publicvoidonLlmError(Exception error){
System.err.println("生成过程出现异常："+ error.getMessage());
}
}

@Component
publicclassStreamingChatService{
    privatefinalObjectMapper objectMapper =newObjectMapper();

    publicvoidhandleUserMessage(String userInput,WebSocketSession session){
        // 创建自定义回调处理器
        WebSocketStreamingHandler handler =newWebSocketStreamingHandler(session);

        // 初始化LLM with streaming
        ChatOpenAI llm =ChatOpenAI.builder()
        .streaming(true)
        .callbacks(Arrays.asList(handler))
        .temperature(0.7)
        .build();

        try{
            // 发送开始标记
            sendMessage(session,newStreamMessage("",true,false));

            // 执行对话
            llm.predict(userInput);

        }catch(Exception e){
            handler.onLlmError(e);
        }
    }

    privatevoidsendMessage(WebSocketSession session,StreamMessage message){
        try{
            String jsonMessage = objectMapper.writeValueAsString(message);
            session.sendMessage(newTextMessage(jsonMessage));
        }catch(Exception e){
            log.error("Failed to send message", e);
        }
    }
}

publicclassWebSocketStreamingHandlerextendsBaseCallbackHandler{
    privatefinalWebSocketSession session;
    privatefinalObjectMapper objectMapper =newObjectMapper();

    publicWebSocketStreamingHandler(WebSocketSession session){
        this.session = session;
    }

    @Override
    publicvoidonLlmNewToken(String token){
    try{
        // 构造实时消息
        StreamMessage message =newStreamMessage(token,false,false);
        String jsonMessage = objectMapper.writeValueAsString(message);

        // 通过WebSocket推送到前端
        session.sendMessage(newTextMessage(jsonMessage));

    }catch(Exception e){
        log.error("Failed to send streaming token", e);
    }
}

@Override
publicvoidonLlmEnd(LlmResult result){
try{
    // 发送结束标记
    StreamMessage endMessage =newStreamMessage("",false,true);
    String jsonMessage = objectMapper.writeValueAsString(endMessage);
    session.sendMessage(newTextMessage(jsonMessage));
}catch(Exception e){
    log.error("Failed to send end message", e);
}
}

@Override
publicvoidonLlmError(Exception error){
    try{
        StreamMessage errorMsg =newStreamMessage(
            "抱歉，生成过程出现异常，请重试",
            true,
            true
        );
        String jsonMessage = objectMapper.writeValueAsString(errorMsg);
        session.sendMessage(newTextMessage(jsonMessage));
    }catch(IOException e){
        log.error("Failed to send error message", e);
    }
}
}

@Data
@AllArgsConstructor
publicclassStreamMessage{
    privateString token;
    privateboolean isError;
    privateboolean isEnd;
}

let currentMessage ='';
const websocket =newWebSocket('ws://localhost:8080/chat');

websocket.onmessage=function(event){
  const data =JSON.parse(event.data);

  if(data.isError){
    showErrorMessage(data.token);
    return;
  }

  if(data.isEnd){
    finishTyping();
    currentMessage ='';// 重置消息
  }else{
    currentMessage += data.token;
    updateChatDisplay(currentMessage);
  }
};

websocket.onclose=function(){
  // 自动重连逻辑
  setTimeout(()=>{
    websocket =newWebSocket('ws://localhost:8080/chat');
  },3000);
};