WebAPI 中的 HttpResponseException
- 你可以在 Action 中使用 HttpResponseException 来包装指定的 HttpCode 和 HttpMessage,如下例子所示:
public Employee GetEmployee(int id)
{
Employee emp = employeeRepository.Get(id);
if (emp == null)
{
var response = new HttpResponseMessage(HttpStatusCode.NotFound)
{
Content = new StringContent("Employee doesn't exist", System.Text.Encoding.UTF8, "text/plain"),
StatusCode = HttpStatusCode.NotFound
}
throw new HttpResponseException(response);
}
return emp;
}
- 如果你的 Action 返回的是 IHttpActionResult,那么可将 GetEmployee() 方法修改如下:
public IHttpActionResult GetEmployee(int id)
{
Employee emp = employeeRepository.Get(id);
if (emp == null)
{
var response = new HttpResponseMessage(HttpStatusCode.NotFound)
{
Content = new StringContent("Employee doesn't exist", System.Text.Encoding.UTF8, "text/plain"),
StatusCode = HttpStatusCode.NotFound
}
throw new HttpResponseException(response);
}
return Ok(emp);
}
从上面的代码可以看出,错误码 和 错误消息 都赋给了 Response 对象,然后包装到了 HttpResponseException 进行返回。
WebAPI 中使用 HttpError
- 除了直接实例化 HttpResponseMessage 类,还可以使用 Request.CreateErrorResponse() 快捷的创建 HttpResponseMessage 类,如下代码所示:
public IActionResult GetEmployee(int id)
{
Employee emp = employeeRepository.Get(id);
if (emp == null)
{
string message = "Employee doesn't exist";
throw new HttpResponseException(
Request.CreateErrorResponse(HttpStatusCode.NotFound, message));
}
return Ok(emp);
}
WebAPI 中使用 异常过滤器
- 异常过滤器是一种可以在 WebAPI 中捕获那些未得到处理的异常的过滤器,要想创建异常过滤器,你需要实现 IExceptionFilter 接口,不过这种方式比较麻烦,更快捷的方法是直接继承 ExceptionFilterAttribute 并重写里面的 OnException() 方法即可,这是因为 ExceptionFilterAttribute 类本身就实现了 IExceptionFilter 接口,如下代码所示:
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, Inherited = true, AllowMultiple = true)]
public abstract class ExceptionFilterAttribute : FilterAttribute, IExceptionFilter, IFilter
{
protected ExceptionFilterAttribute();
public virtual void OnException(HttpActionExecutedContext actionExecutedContext);
public virtual Task OnExceptionAsync(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken);
}
- 下面的代码片段展示了如何通过重写 ExceptionFilterAttribute.OnException() 方法来创建一个自定义异常过滤器,请注意下面的代码是如何捕获在 Action 中抛出的异常,并将捕获到的异常转换为 HttpStatusResponse 实体,然后塞入合适的 httpcode 和 httpmessage,如下代码所示:
public class CustomExceptionFilter : ExceptionFilterAttribute
{
public override void OnException(HttpActionExecutedContext actionExecutedContext)
{
HttpStatusCode status = HttpStatusCode.InternalServerError;
String message = String.Empty;
var exceptionType = actionExecutedContext.Exception.GetType();
if (exceptionType == typeof(UnauthorizedAccessException))
{
message = "Access to the Web API is not authorized.";
status = HttpStatusCode.Unauthorized;
}
else if (exceptionType == typeof(DivideByZeroException))
{
message = "Internal Server Error.";
status = HttpStatusCode.InternalServerError;
}
else
{
message = "Not found.";
status = HttpStatusCode.NotFound;
}
actionExecutedContext.Response = new HttpResponseMessage()
{
Content = new StringContent(message, System.Text.Encoding.UTF8, "text/plain"),
StatusCode = status
};
base.OnException(actionExecutedContext);
}
}
- 接下来将自定义的异常过滤器添加到 HttpConfiguration 全局集合中,如下代码所示:
public static void Register(HttpConfiguration config)
{
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
config.Formatters.Remove(config.Formatters.XmlFormatter);
config.Filters.Add(new CustomExceptionFilter());
}
- 除了将自定义异常设置到全局上,你还可以缩小粒度到 Controller 或者 Action 级别上,下面的代码分别展示了如何将其控制在 Action 和 Controller 上。
[DatabaseExceptionFilter]
public class EmployeesController : ApiController
{
//Some code
}
[CustomExceptionFilter]
public IEnumerable<string> Get()
{
throw new DivideByZeroException();
}
ASP.NET Web API 提供了强大的 HttpResponseException 来包装异常信息,默认情况下,当 WebAPI 中抛出异常,系统默认使用 Http StateCode = 500 作为回应,也即:Internal Server Error. ,场景就来了,如果你会用 HttpResponseException 的话,就可以改变这种系统默认行为,自定义错误码和错误信息让结果更加清晰语义化。