C#调用百度API实现多类型资源搜索指南

一、技术背景与开发价值

在.NET生态中，开发者常面临跨平台资源搜索的需求。百度开放平台提供的Web搜索、图片搜索、视频搜索等API，为C#开发者提供了标准化的数据接口。通过RESTful风格的API调用，开发者可以快速集成百度强大的搜索能力，实现从网页内容抓取到多媒体资源检索的完整功能链。

技术实现上，C#的HttpClient类库提供了高效的HTTP请求支持，配合Newtonsoft.Json进行数据解析，可构建出健壮的搜索服务模块。相比传统爬虫方案，API调用具有数据合法性、结构化输出、服务稳定性等显著优势。

二、开发前准备

2.1 API服务申请

访问百度开发者中心完成实名认证
创建应用获取API Key和Secret Key
申请对应搜索服务的权限（需单独申请图片/视频搜索权限）
配置IP白名单（生产环境必备）

2.2 开发环境配置

<!-- 项目.csproj文件添加NuGet包 -->
<ItemGroup>
    <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
    <PackageReference Include="Microsoft.Extensions.Http" Version="6.0.0" />
</ItemGroup>

三、核心实现方案

3.1 基础请求封装

public class BaiduSearchClient
{
    private readonly string _apiKey;
    private readonly string _secretKey;
    private readonly HttpClient _httpClient;
    public BaiduSearchClient(string apiKey, string secretKey)
    {
        _apiKey = apiKey;
        _secretKey = secretKey;
        _httpClient = new HttpClient();
        _httpClient.DefaultRequestHeaders.Add("User-Agent", "Mozilla/5.0 C# BaiduAPI");
    }
    protected async Task<string> GetAccessTokenAsync()
    {
        var url = $"https://openapi.baidu.com/oauth/2.0/token?grant_type=client_credentials&client_id={_apiKey}&client_secret={_secretKey}";
        var response = await _httpClient.GetStringAsync(url);
        dynamic json = JsonConvert.DeserializeObject(response);
        return json.access_token;
    }
}

3.2 网页搜索实现

public async Task<List<WebResult>> SearchWebAsync(string query, int page = 1, int size = 10)
{
    var token = await GetAccessTokenAsync();
    var url = $"https://openapi.baidu.com/rest/2.0/websearch/websearch?access_token={token}&q={Uri.EscapeDataString(query)}&pn={(page - 1) * size}&rn={size}";
    var response = await _httpClient.GetStringAsync(url);
    dynamic json = JsonConvert.DeserializeObject(response);
    return ((JArray)json.results).Select(x => new WebResult
    {
        Title = x.title.ToString(),
        Url = x.url.ToString(),
        Abstract = x.abstract.ToString()
    }).ToList();
}
public class WebResult
{
    public string Title { get; set; }
    public string Url { get; set; }
    public string Abstract { get; set; }
}

3.3 图片搜索实现

public async Task<List<ImageResult>> SearchImageAsync(string query, string filter = "large", int count = 20)
{
    var token = await GetAccessTokenAsync();
    var url = $"https://openapi.baidu.com/rest/2.0/image-search/v1/search?access_token={token}&word={Uri.EscapeDataString(query)}&rn={count}&tag={filter}";
    var response = await _httpClient.GetStringAsync(url);
    dynamic json = JsonConvert.DeserializeObject(response);
    return ((JArray)json.data).Select(x => new ImageResult
    {
        ThumbnailUrl = x.thumbURL.ToString(),
        HighResUrl = x.middleURL.ToString(),
        Width = (int)x.width,
        Height = (int)x.height
    }).ToList();
}
public class ImageResult
{
    public string ThumbnailUrl { get; set; }
    public string HighResUrl { get; set; }
    public int Width { get; set; }
    public int Height { get; set; }
}

3.4 视频搜索实现

public async Task<List<VideoResult>> SearchVideoAsync(string query, int duration = 0, int page = 1)
{
    var token = await GetAccessTokenAsync();
    var url = $"https://openapi.baidu.com/rest/2.0/video/videosearch?access_token={token}&wd={Uri.EscapeDataString(query)}&pn={(page - 1) * 10}&rn=10";
    if (duration > 0)
    {
        url += $"&duration={duration}";
    }
    var response = await _httpClient.GetStringAsync(url);
    dynamic json = JsonConvert.DeserializeObject(response);
    return ((JArray)json.video).Select(x => new VideoResult
    {
        Title = x.title.ToString(),
        PlayUrl = x.playUrl.ToString(),
        Thumbnail = x.thumbUrl.ToString(),
        Duration = TimeSpan.FromSeconds((double)x.duration)
    }).ToList();
}
public class VideoResult
{
    public string Title { get; set; }
    public string PlayUrl { get; set; }
    public string Thumbnail { get; set; }
    public TimeSpan Duration { get; set; }
}

四、高级功能实现

4.1 异步批量搜索

public async Task<Dictionary<string, List<object>>> BatchSearchAsync(Dictionary<string, string> queries)
{
    var results = new Dictionary<string, List<object>>();
    var tasks = new List<Task>();
    foreach (var query in queries)
    {
        tasks.Add(Task.Run(async () => {
            if (query.Key == "web")
                results[query.Key] = (await SearchWebAsync(query.Value)).Cast<object>().ToList();
            else if (query.Key == "image")
                results[query.Key] = (await SearchImageAsync(query.Value)).Cast<object>().ToList();
        }));
    }
    await Task.WhenAll(tasks);
    return results;
}

4.2 搜索结果缓存

public class SearchCache
{
    private readonly MemoryCache _cache = new MemoryCache(new MemoryCacheOptions());
    public async Task<T> GetOrSetAsync<T>(string cacheKey, Func<Task<T>> acquire, TimeSpan? expiry = null)
    {
        if (_cache.TryGetValue(cacheKey, out T cachedValue))
            return cachedValue;
        var result = await acquire();
        var options = new MemoryCacheEntryOptions
        {
            SlidingExpiration = expiry ?? TimeSpan.FromMinutes(30)
        };
        _cache.Set(cacheKey, result, options);
        return result;
    }
}

五、异常处理与最佳实践

5.1 异常处理机制

public async Task<T> SafeApiCall<T>(Func<Task<T>> apiCall)
{
    try
    {
        return await apiCall();
    }
    catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.Unauthorized)
    {
        throw new ApplicationException("API认证失败，请检查密钥");
    }
    catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.Forbidden)
    {
        throw new ApplicationException("访问权限不足，请检查API权限");
    }
    catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.TooManyRequests)
    {
        throw new ApplicationException("请求过于频繁，请降低调用频率");
    }
    catch (JsonException)
    {
        throw new ApplicationException("API响应格式异常");
    }
}

5.2 性能优化建议

连接复用：配置HttpClient保持长连接

var handler = new HttpClientHandler
{
 PooledConnectionLifetime = TimeSpan.FromMinutes(5),
 PooledConnectionIdleTimeout = TimeSpan.FromMinutes(2)
};
_httpClient = new HttpClient(handler);

并行控制：使用SemaphoreSlim限制并发数
```csharp
private readonly SemaphoreSlim _throttle = new SemaphoreSlim(5);

public async Task ThrottledCall(Func> apiCall)
{
await _throttle.WaitAsync();
try
{
return await apiCall();
}
finally
{
_throttle.Release();
}
}
```

结果分页：合理设置rn参数（每页结果数）
字段过滤：通过rn参数减少不必要的数据传输

六、安全与合规要点

数据脱敏：处理搜索结果时过滤敏感信息
频率限制：遵守百度API的QPS限制（通常5-20次/秒）
日志记录：记录API调用情况便于问题排查
密钥管理：使用Azure Key Vault等安全存储方案

七、扩展应用场景

智能推荐系统：结合用户行为数据进行个性化搜索
内容审核系统：自动过滤违规搜索结果
数据分析平台：收集搜索趋势数据
企业知识库：构建内部搜索系统

八、版本兼容说明

支持.NET Core 3.1及以上版本
兼容.NET Framework 4.6.1及以上版本
百度API v2.0及以上版本

通过上述实现方案，开发者可以快速构建出功能完善的百度搜索服务集成模块。实际开发中建议结合Polly库实现更完善的重试机制，并考虑使用Refit等库简化HTTP调用。对于高并发场景，建议部署API网关进行请求聚合和缓存控制。