为了 顺利迭代升级，web api 在维护过程是不断升级的，但用户是不能强迫他们每次都跟随你去升级，这样会让用户不胜其烦。为了保证不同版本的客户端能同时兼容，在web api接口上加入版本控制就很有必要了。
当然，对于我们开发的代码进行版本控制也有利，不至于陷入混乱。版本参数可以放置在请求的url 作为路由参数的一部分，也可以放在header里。实现的办法是 实现 IHttpControllerSelector 并在WebApiConfig的注册方法里进行替换。
public class VersionHttpControllerSelector : IHttpControllerSelector
{
private const string VersionKey = "version";
private const string ControllerKey = "controller"; private readonly HttpConfiguration _configuration;
private readonly Lazy<Dictionary<string, HttpControllerDescriptor>> _controllers;
private readonly HashSet<string> _duplicates; public VersionHttpControllerSelector(HttpConfiguration config)
{
_configuration = config;
_duplicates = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
_controllers = new Lazy<Dictionary<string, HttpControllerDescriptor>>(InitializeControllerDictionary);
} private Dictionary<string, HttpControllerDescriptor> InitializeControllerDictionary()
{
var dictionary = new Dictionary<string, HttpControllerDescriptor>(StringComparer.OrdinalIgnoreCase);
IAssembliesResolver assembliesResolver = _configuration.Services.GetAssembliesResolver();
IHttpControllerTypeResolver controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();
ICollection<Type> controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver); foreach (Type t in controllerTypes)
{
var segments = t.Namespace.Split(Type.Delimiter); var controllerName = t.Name.Remove(t.Name.Length - DefaultHttpControllerSelector.ControllerSuffix.Length);
string version = segments[segments.Length - ];
var key = String.Format(CultureInfo.InvariantCulture, "{0}.{1}", version, controllerName);
if (version == "Controllers")
{
key = String.Format(CultureInfo.InvariantCulture, "{0}", controllerName);
}
// Check for duplicate keys.
if (dictionary.Keys.Contains(key))
{
_duplicates.Add(key);
}
else
{
dictionary[key] = new HttpControllerDescriptor(_configuration, t.Name, t);
}
}
foreach (string s in _duplicates)
{
dictionary.Remove(s);
}
return dictionary;
} // Get a value from the route data, if present.
private static T GetRouteVariable<T>(IHttpRouteData routeData, string name)
{
object result = null;
if (routeData.Values.TryGetValue(name, out result))
{
return (T)result;
}
return default(T);
} public HttpControllerDescriptor SelectController(HttpRequestMessage request)
{
IHttpRouteData routeData = request.GetRouteData();
if (routeData == null)
{
throw new HttpResponseException(HttpStatusCode.NotFound);
} // Get the version and controller variables from the route data.
string version = GetRouteVariable<string>(routeData, VersionKey);
if (string.IsNullOrEmpty(version))
{
version = GetVersionFromHTTPHeaderAndAcceptHeader(request);
}
string controllerName = GetRouteVariable<string>(routeData, ControllerKey);
if (controllerName == null)
{
throw new HttpResponseException(HttpStatusCode.NotFound);
} // Find a matching controller.
string key = String.Format(CultureInfo.InvariantCulture, "{0}", controllerName);
if (!string.IsNullOrEmpty(version))
{
key = String.Format(CultureInfo.InvariantCulture, "{0}.{1}", version, controllerName);
} HttpControllerDescriptor controllerDescriptor;
if (_controllers.Value.TryGetValue(key, out controllerDescriptor))
{
return controllerDescriptor;
}
else if (_duplicates.Contains(key))
{
throw new HttpResponseException(
request.CreateErrorResponse(HttpStatusCode.InternalServerError,
"Multiple controllers were found that match this request."));
}
else
{
throw new HttpResponseException(HttpStatusCode.NotFound);
}
} public IDictionary<string, HttpControllerDescriptor> GetControllerMapping()
{
return _controllers.Value;
}
private string GetVersionFromHTTPHeaderAndAcceptHeader(HttpRequestMessage request)
{
if (request.Headers.Contains(VersionKey))
{
var versionHeader = request.Headers.GetValues(VersionKey).FirstOrDefault();
if (versionHeader != null)
{
return versionHeader;
}
}
var acceptHeader = request.Headers.Accept;
foreach (var mime in acceptHeader)
{
if (mime.MediaType == "application/json" || mime.MediaType == "text/html")
{
var version = mime.Parameters
.Where(v => v.Name.Equals(VersionKey, StringComparison.OrdinalIgnoreCase))
.FirstOrDefault(); if (version != null)
{
return version.Value;
}
return string.Empty;
}
}
return string.Empty;
}
}
重点是SelectController方法，从http请求里找出合适版本的controller。我这里兼容了从路由和header里获取版本，先从路由里获取，没有再从header里获取。
IHttpRouteData routeData = request.GetRouteData();
if (routeData == null)
{
throw new HttpResponseException(HttpStatusCode.NotFound);
} // Get the version and controller variables from the route data.
string version = GetRouteVariable<string>(routeData, VersionKey);
if (string.IsNullOrEmpty(version))
{
version = GetVersionFromHTTPHeaderAndAcceptHeader(request);
}
private string GetVersionFromHTTPHeaderAndAcceptHeader(HttpRequestMessage request)
{
if (request.Headers.Contains(VersionKey))
{
var versionHeader = request.Headers.GetValues(VersionKey).FirstOrDefault();
if (versionHeader != null)
{
return versionHeader;
}
}
var acceptHeader = request.Headers.Accept;
foreach (var mime in acceptHeader)
{
if (mime.MediaType == "application/json" || mime.MediaType == "text/html")
{
var version = mime.Parameters
.Where(v => v.Name.Equals(VersionKey, StringComparison.OrdinalIgnoreCase))
.FirstOrDefault(); if (version != null)
{
return version.Value;
}
return string.Empty;
}
}
return string.Empty;
}
WebApiConfig文件调用代码如下：
public static void Register(HttpConfiguration config)
{
。。。
config.Services.Replace(typeof(IHttpControllerSelector), new VersionHttpControllerSelector((config))); }
web api的定义呢，则从命名空间上区分就可以了。 比如版本号为V1的 LoginApiController 的命名空间 为定义为 xxx.WebAPI.Controllers.V1，版本号为V2的 LoginApiController 的命名空间 为定义为 xxx.WebAPI.Controllers.V2，如此类推,
客户端在header里加上参数 versoin=v1/v2... 就可以指定使用不同版本的api了。