前言
上次,我们介绍了应该在业务层实现管道模式
响应缓存是ASP.NET Core中很重要的功能,它可以存储响应,并提供来自缓存的响应,以便提高程序性能。
响应缓存通常是通过Middleware实现的:
public static class ResponseCachingExtensions
{/// <summary>/// Adds the <see cref="ResponseCachingMiddleware"/> for caching HTTP responses./// </summary>/// <param name="app">The <see cref="IApplicationBuilder"/>.</param>public static IApplicationBuilder UseResponseCaching(this IApplicationBuilder app){if (app == null){throw new ArgumentNullException(nameof(app));}return app.UseMiddleware<ResponseCachingMiddleware>();}
}
现在,我们改成由业务层实现响应缓存。
实现
1.引用Nuget包
新建WebAPI项目,引用需要的Nuget包:
Install-Package MediatR
Install-Package MediatR.Extensions.Microsoft.DependencyInjection
Install-Package Newtonsoft.Json
2.新增接口
新增ICacheableQuery
接口,表示需要缓存:
public interface ICacheableQuery
{TimeSpan? SlidingExpiration { get; }
}
SlidingExpiration:缓存过期时间
3.新增缓存管道
利用MediatR的IPipelineBehavior功能,实现缓存管道:
public class CachingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse> where TRequest : ICacheableQuery
{private readonly IDistributedCache _cache;public CachingBehavior(IDistributedCache cache){_cache = cache;}public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next){TResponse response;if (request.SlidingExpiration == null){return await next();}var key =GetCacheKey(request);var cachedResponse = await _cache.GetAsync(key, cancellationToken);if (cachedResponse != null){response = JsonConvert.DeserializeObject<TResponse>(Encoding.UTF8.GetString(cachedResponse));}else{response = await next();var options = new DistributedCacheEntryOptions { SlidingExpiration = request.SlidingExpiration };var serializedData = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(response));await _cache.SetAsync(key, serializedData, options, cancellationToken);return response;}return response;}
}
以TRequest作为缓存Key,如果缓存存在,则反序列化得到缓存的响应,否则执行请求,缓存响应。
4.使用缓存管道
修改WeatherForecastController,使用Mediator,设置缓存时间为5秒:
public class WeatherForecastController : ControllerBase
{private readonly IMediator _mediator;public WeatherForecastController(IMediator mediator){this._mediator = mediator;}[HttpGet]public async Task<IEnumerable<WeatherForecast>> Get(){return await this._mediator.Send(new GetWeatherForecastQuery()); }
}public class GetWeatherForecastQuery : IRequest<IEnumerable<WeatherForecast>>, ICacheableQuery
{public TimeSpan? SlidingExpiration { get; set; } = TimeSpan.FromSeconds(5);
}internal class GetWeatherForecastQueryHandler : IRequestHandler<GetWeatherForecastQuery, IEnumerable<WeatherForecast>>
{public async Task<IEnumerable<WeatherForecast>> Handle(GetWeatherForecastQuery request, CancellationToken cancellationToken){await Task.Delay(1000);var rng = new Random();return Enumerable.Range(1, 1).Select(index => new WeatherForecast{ TemperatureC = rng.Next(-20, 55),Summary = Summaries[rng.Next(Summaries.Length)]}).ToArray();}
}
为了体现效果明显,代码里故意加了等待时间。
运行程序,可以看到,第一次请求花了1000多ms,而后的请求都很快,说明使用了缓存:
结论
在本文中,我们学会了使用MediatR实现响应缓存。
如果你觉得这篇文章对你有所启发,请关注我的个人公众号”My IO“