基于React + FastAPI + LangChain + 通义千问的智能医疗问答系统

📌 文章摘要：

本文详细介绍了如何在前端通过 Fetch 实现与 FastAPI 后端的 流式响应通信，并支持图文多模态数据上传。通过构建 multipart/form-data 请求，配合 ReadableStream 实时读取 AI 回复内容，实现类似 ChatGPT 的对话效果。同时提供完整的接口调用代码和 UI 展示逻辑，帮助开发者快速搭建自然流畅的 AI 医疗助手交互界面。

正常提问

经过RAG处理提问

项目简介

AI医疗助手是一个结合了最新人工智能技术的医疗问答系统，旨在为用户提供准确、专业的医疗咨询服务。系统采用前后端分离架构，前端使用React构建友好的用户界面，后端使用FastAPI提供高性能的API服务，并结合LangChain框架和通义千问大语言模型提供智能问答能力。本项目是本人用于学习LangChain框架的练手项目，后续会继续完善。

核心功能

• 🩺 医疗问答：针对用户的医疗问题提供专业解答
• 💬 实时对话：流式响应，打字机效果，提升用户体验
• 🧠 上下文记忆：支持多轮对话，理解上下文信息
• 📚 知识检索：基于RAG技术，从医疗知识库中检索相关信息
• 🎨 美观界面：现代化的聊天UI，支持Markdown渲染
• 🔄 对话记忆：自动保存对话历史，支持会话恢复

技术栈

前端

• 框架：React 19 + TypeScript
• 状态管理：React Hooks
• 样式：CSS Modules
• 网络请求：Fetch API（支持流式响应）
• 组件：
  • 自定义聊天界面
  • Markdown渲染 (react-markdown)
  • 弹窗组件
  • 消息提示 (react-hot-toast)

后端

• 框架：FastAPI (Python)
• AI框架：LangChain 0.3.0
• 大语言模型：通义千问 (qwen-turbo/qwen-plus/qwen-max)
• 向量数据库：Chroma
• 文本嵌入：DashScope Embeddings
• 流式响应：SSE (Server-Sent Events)
• 文档处理：LangChain Text Splitters

系统架构

✅ 2. 核心功能组件代码展示

App.css

/* 基础布局样式 */

.App {
    text-align: center;
    display: flex;
    flex-direction: column;
    height: 100vh;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: #f8fbfd;
}


/* 头部样式 */

.App-header {
    background-color: #1e88e5;
    background-image: linear-gradient(135deg, #1e88e5 0%, #0d47a1 100%);
    min-height: 80px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    color: white;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    padding: 12px 20px;
    position: relative;
}

.App-header::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, #29b6f6, #4fc3f7, #81d4fa);
}

.logo-container {
    display: flex;
    align-items: center;
    gap: 10px;
}

.logo-icon {
    font-size: 28px;
}

.App-header h1 {
    margin: 0;
    font-size: 1.8rem;
    font-weight: 600;
    letter-spacing: 0.5px;
}

.header-subtitle {
    font-size: 0.9rem;
    opacity: 0.9;
    margin-top: 4px;
    font-weight: 400;
}


/* 主体内容样式 */

main {
    flex-grow: 1;
    display: flex;
    flex-direction: column;
    max-width: 1100px;
    width: 100%;
    margin: 0 auto;
    padding: 0;
    position: relative;
}

main>div {
    flex-grow: 1;
    height: 100%;
    border-radius: 12px;
    margin: 15px;
    overflow: hidden;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
    background-color: white;
    border: 1px solid #e0e6ed;
}


/* 底部样式 */

.App-footer {
    background-color: #f1f5f9;
    color: #64748b;
    font-size: 0.8rem;
    padding: 12px;
    text-align: center;
    border-top: 1px solid #e2e8f0;
}


/* 响应式设计 */

@media (max-width: 768px) {
    .App-header {
        padding: 10px;
        min-height: 60px;
    }
    .App-header h1 {
        font-size: 1.4rem;
    }
    .logo-icon {
        font-size: 24px;
    }
    main>div {
        margin: 8px;
        border-radius: 8px;
    }
    .header-subtitle {
        font-size: 0.8rem;
    }
}

@media (max-width: 480px) {
    .App-header h1 {
        font-size: 1.2rem;
    }
    .logo-icon {
        font-size: 20px;
    }
    main>div {
        margin: 4px;
        border-radius: 6px;
    }
    .header-subtitle {
        display: none;
    }
}

MessageList.css

.message-list {
    display: flex;
    flex-direction: column;
    padding: 1rem;
    overflow-y: auto;
    flex: 1;
    max-height: calc(100vh - 170px);
}

.message {
    margin-bottom: 1rem;
    display: flex;
    flex-direction: column;
    max-width: 80%;
}

.user-message {
    align-self: flex-end;
}

.assistant-message {
    align-self: flex-start;
}

.message-content {
    padding: 0.8rem;
    border-radius: 8px;
    box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1);
}

.user-message .message-content {
    background-color: #e3f2fd;
    color: #0d47a1;
}

.assistant-message .message-content {
    background-color: #f5f5f5;
    color: #333;
}

.message-header {
    display: flex;
    justify-content: space-between;
    margin-bottom: 0.5rem;
    font-size: 0.8rem;
    color: #666;
}

.message-role {
    font-weight: bold;
}

.message-time {
    font-size: 0.7rem;
}

.message-text {
    white-space: pre-wrap;
    word-break: break-word;
    line-height: 1.5;
}

.empty-messages {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100%;
    color: #9e9e9e;
    text-align: center;
    padding: 2rem;
}

.empty-messages p {
    font-size: 1.1rem;
    margin-bottom: 1rem;
}

ChatInput.css

.chat-input-form {
    padding: 1rem;
    border-top: 1px solid #eaeaea;
    background-color: #fff;
}

.input-container {
    display: flex;
    position: relative;
}

.message-input {
    flex: 1;
    min-height: 60px;
    max-height: 200px;
    padding: 12px;
    border: 1px solid #ccc;
    border-radius: 8px;
    resize: vertical;
    font-family: inherit;
    font-size: 1rem;
    outline: none;
    transition: border-color 0.3s;
}

.message-input:focus {
    border-color: #2196f3;
}

.message-input:disabled {
    background-color: #f9f9f9;
    cursor: not-allowed;
}

.send-button {
    margin-left: 10px;
    padding: 0 20px;
    height: 40px;
    align-self: flex-end;
    background-color: #2196f3;
    color: white;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    font-weight: bold;
    transition: background-color 0.3s;
}

.send-button:hover:not(:disabled) {
    background-color: #0d8bf2;
}

.send-button:disabled {
    background-color: #cccccc;
    cursor: not-allowed;
}

.input-help-text {
    margin-top: 0.5rem;
    font-size: 0.75rem;
    color: #757575;
    text-align: right;
}

ChatInterface.css

.chat-container {
    display: flex;
    flex-direction: column;
    /* height: 100vh; */
    width: 100%;
    max-height: 86vh;
    background-color: #f8fbfd;
    position: relative;
    overflow: hidden;
}


/* 聊天历史区域 */

.messages-container {
    flex: 1;
    overflow-y: auto;
    padding: 2rem;
    padding-bottom: 2rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
    scrollbar-width: thin;
    scrollbar-color: rgba(0, 0, 0, 0.2) transparent;
    scroll-behavior: smooth;
    background-image: linear-gradient(rgba(255, 255, 255, 0.8) 0%, rgba(255, 255, 255, 0.9) 100%), url('data:image/svg+xml;utf8,<svg width="100" height="100" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg"><path d="M10 10h10v10H10zM30 10h10v10H30zM50 10h10v10H50zM70 10h10v10H70zM20 20h10v10H20zM40 20h10v10H40zM60 20h10v10H60zM80 20h10v10H80zM10 30h10v10H10zM30 30h10v10H30zM50 30h10v10H50zM70 30h10v10H70z" fill="%23E3F2FD" fill-opacity="0.1"/></svg>');
}


/* 美化滚动条 */

.messages-container::-webkit-scrollbar {
    width: 6px;
}

.messages-container::-webkit-scrollbar-track {
    background: transparent;
}

.messages-container::-webkit-scrollbar-thumb {
    background-color: rgba(0, 0, 0, 0.2);
    border-radius: 3px;
}

.messages-container::-webkit-scrollbar-thumb:hover {
    background: #a1c4e4;
}


/* 消息气泡容器 */

.message {
    max-width: 85%;
    display: flex;
    flex-direction: column;
    position: relative;
    animation: fadeIn 0.3s ease-out;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.message.user {
    align-self: flex-end;
}

.message.assistant {
    align-self: flex-start;
}

.message.system {
    align-self: center;
    max-width: 90%;
    margin: 8px 0;
}


/* 消息气泡 */

.message-bubble {
    padding: 14px 16px;
    border-radius: 18px;
    word-break: break-word;
    line-height: 1.5;
    position: relative;
    font-size: 15px;
    letter-spacing: 0.2px;
    transition: all 0.2s ease;
    text-align: left;
}


/* 用户消息气泡 */

.user .message-bubble {
    background-color: #0d6efd;
    color: white;
    border-bottom-right-radius: 4px;
    box-shadow: 0 2px 8px rgba(13, 110, 253, 0.2);
}


/* 助手消息气泡 */

.assistant .message-bubble {
    background-color: #e9f3ff;
    color: #0a2642;
    border-bottom-left-radius: 4px;
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
    border-left: 3px solid #4dabf7;
}

.assistant .message-bubble::before {
    content: '🩺';
    position: absolute;
    left: -30px;
    top: 2px;
    font-size: 16px;
    color: #4dabf7;
    background: white;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}


/* 系统消息气泡 */

.system .message-bubble {
    background-color: #fff3cd;
    color: #856404;
    border-radius: 10px;
    border-left: 3px solid #ffc107;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
}


/* 消息信息 */

.message-info {
    font-size: 12px;
    color: #8e8e93;
    margin-top: 4px;
    padding: 0 8px;
    display: flex;
    align-items: center;
}

.user .message-info {
    justify-content: flex-end;
}


/* 输入区域 */

.input-container {
    flex-shrink: 0;
    padding: 1rem;
    background-color: white;
    border-top: 1px solid #e0e6ed;
    display: flex;
    gap: 10px;
    z-index: 100;
    position: sticky;
    bottom: 0;
    left: 0;
    right: 0;
    width: 100%;
    /* box-shadow: 0 -2px 10px rgba(0, 0, 0, 0.05); */
}

.input-container::before {
    content: '';
    position: absolute;
    top: -20px;
    left: 0;
    right: 0;
    height: 20px;
    background: linear-gradient(to bottom, rgba(248, 251, 253, 0), rgba(248, 251, 253, 1));
    pointer-events: none;
}

.input-container input {
    flex: 1;
    border: 1px solid #d1e3f8;
    padding: 12px 16px;
    border-radius: 24px;
    background-color: #f8fbfd;
    margin-right: 10px;
    font-size: 15px;
    outline: none;
    transition: all 0.2s ease;
    color: #0a2642;
}

.input-container input:focus {
    border-color: #4dabf7;
    box-shadow: 0 0 0 3px rgba(77, 171, 247, 0.2);
    background-color: white;
}

.input-container input::placeholder {
    color: #99b2cc;
}

.input-container button {
    background-color: #0d6efd;
    color: white;
    border: none;
    border-radius: 24px;
    padding: 0 24px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    height: 42px;
}

.input-container button:hover:not(:disabled) {
    background-color: #0b5ed7;
    transform: translateY(-1px);
    box-shadow: 0 2px 5px rgba(11, 94, 215, 0.3);
}

.input-container button:active:not(:disabled) {
    transform: translateY(0);
    box-shadow: none;
}

.input-container button:disabled {
    background-color: #b9d7ff;
    cursor: not-allowed;
}


/* 打字指示器动画 */

.typing-indicator {
    display: inline-block;
    position: relative;
    width: 60px;
    height: 24px;
}

.typing-indicator::before {
    content: "";
    position: absolute;
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background-color: #4dabf7;
    left: 0;
    animation: typing-dot 1.4s infinite ease-in-out both;
    animation-delay: -0.32s;
}

.typing-indicator::after {
    content: "";
    position: absolute;
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background-color: #4dabf7;
    right: 0;
    animation: typing-dot 1.4s infinite ease-in-out both;
    animation-delay: 0s;
}

.typing-indicator span {
    position: absolute;
    top: 0;
    width: 10px;
    height: 10px;
    border-radius: 50%;
    background-color: #4dabf7;
    left: 22px;
    animation: typing-dot 1.4s infinite ease-in-out both;
    animation-delay: -0.16s;
}

@keyframes typing-dot {
    0%,
    80%,
    100% {
        transform: scale(0.7);
        opacity: 0.6;
    }
    40% {
        transform: scale(1);
        opacity: 1;
    }
}


/* 响应式设计 */

@media (max-width: 768px) {
    .message-bubble {
        padding: 12px 14px;
        font-size: 14px;
    }
    .assistant .message-bubble::before {
        display: none;
    }
    .input-container {
        padding: 12px;
    }
    .input-container input {
        padding: 10px 14px;
    }
    .input-container button {
        padding: 0 16px;
        height: 38px;
    }
}

@media (max-width: 480px) {
    .messages-container {
        padding: 15px 10px;
    }
    .message {
        max-width: 90%;
    }
    .message-bubble {
        padding: 10px 12px;
        font-size: 14px;
    }
    .input-container input {
        padding: 10px 12px;
    }
    .input-container button {
        padding: 0 15px;
        font-size: 14px;
    }
}

.chat-header {
    padding: 1rem;
    background-color: #2196f3;
    color: white;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    flex-shrink: 0;
    z-index: 10;
}

.chat-header h1 {
    margin: 0;
    font-size: 1.5rem;
    font-weight: 500;
}

.conversation-id {
    font-size: 0.8rem;
    opacity: 0.8;
}

.error-message {
    padding: 0.8rem;
    margin: 0.5rem 1rem;
    background-color: #ffebee;
    color: #c62828;
    border-radius: 4px;
    font-size: 0.9rem;
}


/* Markdown样式 */

.markdown-content {
    margin: 0;
    line-height: 1.5;
    text-align: left;
}

.markdown-content p,
.markdown-content ul,
.markdown-content ol,
.markdown-content h1,
.markdown-content h2,
.markdown-content h3,
.markdown-content h4,
.markdown-content h5,
.markdown-content h6 {
    text-align: left;
}

.markdown-content p {
    margin: 0 0 0.8em;
}

.markdown-content p:last-child {
    margin-bottom: 0;
}

.markdown-content h1,
.markdown-content h2,
.markdown-content h3,
.markdown-content h4,
.markdown-content h5,
.markdown-content h6 {
    margin-top: 1em;
    margin-bottom: 0.5em;
    font-weight: 600;
    line-height: 1.25;
    color: #003366;
}

.markdown-content h1 {
    font-size: 1.5em;
}

.markdown-content h2 {
    font-size: 1.3em;
}

.markdown-content h3 {
    font-size: 1.1em;
}

.markdown-content ul,
.markdown-content ol {
    margin-top: 0;
    margin-bottom: 1em;
    padding-left: 2em;
}

.markdown-content li {
    margin: 0.3em 0;
}

.markdown-content a {
    color: #0d6efd;
    text-decoration: none;
}

.markdown-content a:hover {
    text-decoration: underline;
}

.markdown-content blockquote {
    margin: 0.8em 0;
    padding: 0 1em;
    color: #0d47a1;
    border-left: 3px solid #90caf9;
    background-color: rgba(144, 202, 249, 0.1);
}

.markdown-content code {
    font-family: monospace;
    padding: 0.2em 0.4em;
    margin: 0;
    font-size: 85%;
    border-radius: 3px;
    background-color: rgba(0, 0, 0, 0.05);
    color: #d32f2f;
}

.markdown-content pre {
    margin: 0.8em 0;
    padding: 0.8em;
    overflow: auto;
    background-color: #f1f5f9;
    border-radius: 4px;
}

.markdown-content pre code {
    padding: 0;
    background-color: transparent;
    color: #0a2642;
}

.markdown-content table {
    border-collapse: collapse;
    width: 100%;
    margin: 1em 0;
}

.markdown-content table th,
.markdown-content table td {
    padding: 6px 12px;
    border: 1px solid #e0e6ed;
    text-align: left;
}

.markdown-content table th {
    background-color: rgba(77, 171, 247, 0.1);
    font-weight: 600;
}

.markdown-content table tr:nth-child(even) {
    background-color: rgba(244, 247, 250, 0.7);
}

.markdown-content img {
    max-width: 100%;
    height: auto;
    border-radius: 4px;
    margin: 0.5em 0;
}

.markdown-content hr {
    height: 1px;
    margin: 1em 0;
    background-color: #e0e6ed;
    border: none;
}


/* 医疗相关样式 */

.markdown-content .highlight-warning {
    background-color: #fff3cd;
    padding: 8px 12px;
    border-radius: 4px;
    border-left: 3px solid #ffc107;
    margin: 0.8em 0;
}

.markdown-content .highlight-info {
    background-color: #e9f3ff;
    padding: 8px 12px;
    border-radius: 4px;
    border-left: 3px solid #4dabf7;
    margin: 0.8em 0;
}


/* 医疗专业术语 */

.markdown-content .medical-term {
    border-bottom: 1px dashed #4dabf7;
}


/* 响应式样式 */

@media (max-width: 768px) {
    .markdown-content h1 {
        font-size: 1.3em;
    }
    .markdown-content h2 {
        font-size: 1.2em;
    }
    .markdown-content h3 {
        font-size: 1.1em;
    }
    .markdown-content pre {
        padding: 0.6em;
    }
    .markdown-content blockquote {
        padding: 0 0.8em;
    }
}


/* 添加头部样式 */

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 20px;
    background-color: #f0f8ff;
    border-bottom: 1px solid #e0e6ed;
}

.title {
    font-size: 1.5rem;
    font-weight: 600;
    color: #003366;
}

.actions {
    display: flex;
    gap: 12px;
}


/* 流式响应开关样式 */

.stream-toggle {
    display: flex;
    align-items: center;
}

.toggle-label {
    display: flex;
    align-items: center;
    cursor: pointer;
    font-size: 0.9rem;
    color: #444;
}

.toggle-label input[type="checkbox"] {
    margin-right: 6px;
    width: 16px;
    height: 16px;
    cursor: pointer;
}

.toggle-label input[type="checkbox"]:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.toggle-label input[type="checkbox"]:checked+span {
    color: #0078d7;
    font-weight: 500;
}


/* 消息图片样式 */

.message-image-container {
    margin-bottom: 8px;
    max-width: 100%;
}

.message-image {
    max-width: 100%;
    max-height: 300px;
    border-radius: 8px;
    cursor: pointer;
}


/* 图片预览区域 */

.image-preview-container {
    margin: 0 16px;
    padding: 8px;
    position: relative;
    display: inline-block;
    max-width: 150px;
    margin-bottom: 8px;
}

.image-preview {
    width: 100%;
    max-height: 150px;
    object-fit: contain;
    border-radius: 8px;
    border: 1px solid #e1e1e1;
}

.clear-image-button {
    position: absolute;
    top: 0;
    right: 0;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    background-color: rgba(0, 0, 0, 0.5);
    color: white;
    border: none;
    font-size: 16px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
}

.clear-image-button:hover {
    background-color: rgba(0, 0, 0, 0.7);
}


/* 输入区域样式 */

.input-container {
    display: flex;
    padding: 12px 16px;
    border-top: 1px solid #e1e1e1;
    background-color: #f9f9f9;
    align-items: center;
}

.input-container input[type="text"] {
    flex: 1;
    padding: 10px 16px;
    border: 1px solid #d1d1d1;
    border-radius: 20px;
    font-size: 16px;
    outline: none;
    transition: border 0.3s;
}

.input-container input[type="text"]:focus {
    border-color: #4a89dc;
}

.input-container input[type="text"].with-image {
    border-color: #4a89dc;
    background-color: #f0f7ff;
}


/* 图片上传按钮 */

.image-upload-button {
    width: 38px;
    height: 38px;
    border-radius: 50%;
    background-color: #f0f0f0;
    border: 1px solid #d1d1d1;
    margin-right: 10px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 0;
}

.image-upload-button svg {
    fill: #5a5a5a;
    width: 20px;
    height: 20px;
}

.image-upload-button:hover {
    background-color: #e3e3e3;
}

.image-upload-button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}


/* 发送按钮 */

.send-button {
    margin-left: 10px;
    padding: 10px 20px;
    background-color: #4a89dc;
    color: white;
    border: none;
    border-radius: 20px;
    font-weight: 500;
    cursor: pointer;
    transition: background-color 0.3s;
}

.send-button:hover {
    background-color: #3a79d2;
}

.send-button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}


/* 流式响应开关 */

.stream-toggle {
    display: flex;
    align-items: center;
    margin-right: 10px;
}

.toggle-label {
    display: flex;
    align-items: center;
    cursor: pointer;
    font-size: 14px;
    color: #666;
}

.toggle-label input {
    margin-right: 6px;
}


/* 响应式设计调整 */

@media (max-width: 600px) {
    .image-upload-button {
        width: 34px;
        height: 34px;
    }
    .image-upload-button svg {
        width: 18px;
        height: 18px;
    }
    .send-button {
        padding: 8px 12px;
        font-size: 14px;
    }
}

✅ 3. API 接口调用代码（Fetch 流式响应）

在本项目中，我们通过 FastAPI 搭建了一个支持多模态聊天（图文）和图生图的 AI 医疗助手系统。前端使用 Fetch 实现与后端的流式响应通信，实现了更自然的人机交互体验。

本文将聚焦于前端调用后端接口的 流式响应实现方式，并结合项目的接口说明，展示完整的调用代码和注意事项。

🧠 为什么选择流式响应？

传统的 HTTP 请求是在服务端处理完所有数据后一次性返回，而 流式响应（Streaming Response） 能够实现像 ChatGPT 一样 “字一个一个地出来”，提高用户体验。

流式的技术基础：

• 服务端使用 yield 或 StreamingResponse 分块发送数据；

• 客户端使用 Fetch + ReadableStream 实现逐块接收并展示内容。

🛠️ 后端接口回顾

POST /api/chat/multimodal
Content-Type: multipart/form-data
Form fields:
- conversation_id: string
- text: string
- image: file (optional)

Response: 流式返回 AI 回复内容

📜 前端 Fetch 调用示例（流式读取）

const controller = new AbortController(); // 用于中止请求
const signal = controller.signal;

async function chatWithAI({ conversationId, inputText, imageFile }) {
  const formData = new FormData();
  formData.append("conversation_id", conversationId);
  formData.append("text", inputText);
  if (imageFile) {
    formData.append("image", imageFile);
  }

  const response = await fetch("http://localhost:8000/api/chat/multimodal", {
    method: "POST",
    body: formData,
    signal,
  });

  if (!response.ok) {
    throw new Error("请求失败: " + response.statusText);
  }

  const reader = response.body.getReader();
  const decoder = new TextDecoder("utf-8");
  let resultText = "";

  while (true) {
    const { value, done } = await reader.read();
    if (done) break;
    const chunk = decoder.decode(value, { stream: true });
    resultText += chunk;

    // 你可以在此处逐步展示文本（如更新 chat UI）
    appendToChatUI(chunk);
  }

  return resultText;
}

📦 UI 使用场景示例

<input type="file" id="imageInput" />
<input type="text" id="textInput" placeholder="请输入咨询内容" />
<button onclick="handleSubmit()">发送</button>
<div id="chatBox"></div>

<script>
  async function handleSubmit() {
    const imageInput = document.getElementById("imageInput").files[0];
    const text = document.getElementById("textInput").value;
    const chatBox = document.getElementById("chatBox");

    chatBox.innerHTML += "<div class='user-msg'>" + text + "</div>";

    try {
      await chatWithAI({
        conversationId: "user-session-123",
        inputText: text,
        imageFile: imageInput
      });
    } catch (err) {
      console.error("请求失败", err);
    }
  }

  function appendToChatUI(textChunk) {
    let botMsg = document.querySelector(".bot-msg:last-child");
    if (!botMsg || botMsg.getAttribute("finished")) {
      botMsg = document.createElement("div");
      botMsg.className = "bot-msg";
      document.getElementById("chatBox").appendChild(botMsg);
    }
    botMsg.innerText += textChunk;
  }
</script>