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第一步：在webAPI中安装 Autofac.WebApi2 。

不要错误的安装Autofac.Mvc5，也不要错误的安装Autofac.WebApi，因为Autofac.WebApi是给webapi1的，否则会报错：重写成员“Autofac.Integration.WebApi.AutofacWebApiDependencyResolver.BeginScope()”时违反了继承安全

第二步：在App_Start中创建一个类 ：取名AutoFacConfig

第三步：引入 using Autofac;  using Autofac.Integration.WebApi;

namespace WebApi.App_Start
{public class AutoFacConfig{public static void InitAutoFac(){//得到你的HttpConfiguration.var configuration = GlobalConfiguration.Configuration;var builder = new ContainerBuilder();//注册控制器builder.RegisterApiControllers(Assembly.GetExecutingAssembly()).PropertiesAutowired();//可选：注册Autofac过滤器提供商.builder.RegisterWebApiFilterProvider(configuration);//builder.RegisterType(typeof(MyAuthenticationAttribute)).PropertiesAutowired(); //单独注册我们的MyAuthenticationAttribute过滤器var webapiAssembly = Assembly.Load("WebApi");//注册webapi项目中现实了IAuthorizationFilter接口或者实现了IActionFilter接口的非抽象过滤器类builder.RegisterAssemblyTypes(webapiAssembly).Where(r => !r.IsAbstract &&(typeof(IAuthorizationFilter).IsAssignableFrom(r)) || typeof(IActionFilter).IsAssignableFrom(r)).PropertiesAutowired();//对Repositorys这个程序集实现了IBaseRepository接口的非抽象类进行注册var repository = Assembly.Load("Repositorys");builder.RegisterAssemblyTypes(repository).Where(r => !r.IsAbstract).AsImplementedInterfaces().SingleInstance().PropertiesAutowired();IContainer container = builder.Build();//将依赖关系解析器设置为Autofac。var resolver = new AutofacWebApiDependencyResolver(container);configuration.DependencyResolver = resolver;}}
}

第四步：在Global.asax中引用执行。

namespace WebApi
{public class WebApiApplication : System.Web.HttpApplication{protected void Application_Start(){AutoFacConfig.InitAutoFac();//调用InitAutoFac()方法执行GlobalConfiguration.Configure(WebApiConfig.Register);}}
}

在过滤器中使用属性注入（特别注意过滤器的注册，过滤器对象最好不要直接new，而是去IOC容器中拿，否则不能直接在过滤器中使用属性注入）

例如：我创建了一个身份验证过滤器，如果过滤器中使用了属性依赖注入，那么注册这个过滤器的时候需要从IOC容器中去拿这个过滤器类对象的实例，不能直接new

namespace WebApi
{public class MyAuthenticationAttribute : IAuthorizationFilter//也可以直接继承AuthorizationFilterAttribute{public IAppInfosRepository app { get; set; }public bool AllowMultiple => true;public async Task<HttpResponseMessage> ExecuteAuthorizationFilterAsync(HttpActionContext actionContext, CancellationToken cancellationToken, Func<Task<HttpResponseMessage>> continuation){//获得报文头中的AppKey和Sign （我们与客户端约定，在向服务端发起请求的时候，将AppKey和Sign放到请求报文头中）IEnumerable<string> appKeys;if (!actionContext.Request.Headers.TryGetValues("AppKey", out appKeys)) //从请求报文头中获取AppKey{{return new HttpResponseMessage(System.Net.HttpStatusCode.Unauthorized) { Content = new StringContent("报文头中的AppKey为空") };}}IEnumerable<string> signs;if (!actionContext.Request.Headers.TryGetValues("Sign", out signs)) //从请求报文头中获取Sign{return new HttpResponseMessage(System.Net.HttpStatusCode.Unauthorized) { Content = new StringContent("报文头中的Sign为空") };}string appKey = appKeys.First();string sign = signs.First();var appInfo = await app.GetByAppKeyAsync(appKey);//从数据库获取appinfo这条数据（获取AppKey，AppSecret信息）if (appInfo == null){return new HttpResponseMessage(System.Net.HttpStatusCode.Unauthorized) { Content = new StringContent("不存在的AppKey") };}if (appInfo.IsEnable == "true"){return new HttpResponseMessage(System.Net.HttpStatusCode.Forbidden) { Content = new StringContent("AppKey已经被封禁") };}string requestDataStr = ""; //请求参数字符串List<KeyValuePair<string, string>> requestDataList = new List<KeyValuePair<string, string>>();//请求参数键值对if (actionContext.Request.Method == HttpMethod.Post) //如果是Post请求{//获取Post请求数据  requestDataStr = GetRequestValues(actionContext);if (requestDataStr.Length > 0){string[] requestParamsKv = requestDataStr.Split('&');foreach (var item in requestParamsKv){string[] pkv = item.Split('=');requestDataList.Add(new KeyValuePair<string, string>(pkv[0], pkv[1]));}//requestDataList就是按照key（参数的名字）进行排序的请求参数集合   requestDataList = requestDataList.OrderBy(kv => kv.Key).ToList();var segments = requestDataList.Select(kv => kv.Key + "=" + kv.Value);//拼接key=value的数组requestDataStr = string.Join("&", segments);//用&符号拼接起来}}if (actionContext.Request.Method == HttpMethod.Get) //如果是Get请求{//requestDataList就是按照key（参数的名字）进行排序的请求参数集合          requestDataList = actionContext.Request.GetQueryNameValuePairs().OrderBy(kv => kv.Key).ToList();var segments = requestDataList.Select(kv => kv.Key + "=" + kv.Value);//拼接key=value的数组requestDataStr = string.Join("&", segments);//用&符号拼接起来}//计算Sign （即：计算requestDataStr+AppSecret的md5值）string computedSign = MD5Helper.ComputeMd5(requestDataStr + appInfo.AppSecret);//用户传进来md5值和计算出来的比对一下，就知道数据是否有被篡改过if (sign.Equals(computedSign, StringComparison.CurrentCultureIgnoreCase)){return await continuation();}else{return new HttpResponseMessage(System.Net.HttpStatusCode.Unauthorized) { Content = new StringContent("sign验证失败") };}}/// <summary>/// 获取Post请求的请求参数内容/// 参考资料：https://www.cnblogs.com/hnsongbiao/p/7039666.html/// </summary>/// <param name="actionContext"></param>/// <returns></returns>public string GetRequestValues(HttpActionContext actionContext){Stream stream = actionContext.Request.Content.ReadAsStreamAsync().Result;Encoding encoding = Encoding.UTF8;/*这个StreamReader不能关闭，也不能dispose， 关了就傻逼了因为你关掉后，后面的管道  或拦截器就没办法读取了所有这里不要用usingusing (StreamReader reader = new StreamReader(stream, System.Text.Encoding.UTF8)){result = reader.ReadToEnd().ToString();}*/var reader = new StreamReader(stream, encoding);string result = reader.ReadToEnd();/*这里也要注意：   stream.Position = 0;当你读取完之后必须把stream的位置设为开始因为request和response读取完以后Position到最后一个位置，交给下一个方法处理的时候就会读不到内容了。*/stream.Position = 0;return result;}}
}

在WebApiConfig.cs类中注册这个过滤器 （统一注册过滤器）

namespace WebApi
{public static class WebApiConfig{public static void Register(HttpConfiguration config){// Web API 配置和服务// Web API 路由config.MapHttpAttributeRoutes();config.Routes.MapHttpRoute(name: "DefaultApi",routeTemplate: "api/{controller}/{id}",defaults: new { id = RouteParameter.Optional });//从Autofac的IOC容器中拿到MyAuthenticationAttribute过滤器的类对象//MyAuthenticationAttribute authorFilter = (MyAuthenticationAttribute)GlobalConfiguration.Configuration.DependencyResolver.GetService(typeof(MyAuthenticationAttribute));//config.Filters.Add(authorFilter); //注册过滤器//注意：如果想在过滤器中使用属性注入，则注册这个过滤器的时候，这个过滤器的对象必须要用IOC容器过得到            //不能直接new 例如:不能直接config.Filters.Add(new MyAuthenticationAttribute())//因为一个对象必须是由IOC容器创建出来的，IOC容器才会自动帮我们注入#region 统一注册过滤器var webapiAss = Assembly.Load("WebApi");//从webapiAss中拿到所有实现了IAuthorizationFilter接口，或者实现了IActionFilter接口的非抽象过滤器类var filters = webapiAss.GetTypes().Where(r => !r.IsAbstract && (typeof(IAuthorizationFilter).IsAssignableFrom(r) || typeof(IActionFilter).IsAssignableFrom(r)));foreach (var item in filters){//从IOC容器中拿到过滤器类对象（因为过滤器都是实现了IFilter接口的，所有这里以IFilter接口来接收）IFilter filter = (IFilter)GlobalConfiguration.Configuration.DependencyResolver.GetService(item);config.Filters.Add(filter); //注册过滤器} #endregion}}
}