WCF4.0 -- RESTful WCF Services 错误处理 (Error Handling)

REST WCF 的错误处理可用于从 WCF Web HTTP 服务返回指定 HTTP 状态代码的错误，并且返回的错误详细信息使用与操作相同的格式（如 XML 或 JSON）。在WCF 4.0中增加了WebFaultException<T>异常类，我们可以更加方便的处理错误，并能给予客户端详细的错误提示。

服务端代码：

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1. //当查不到User时，抛出WebFaultException，并提示NotFound及错误信息 
2. [WebGet(UriTemplate="/Users/{name}")] 
3. public User GetUser(string name) 
4. { 
5.     var user = Users.FirstOrDefault(u => u.Name == name); 
6.     if (user == null) 
7.         throw new WebFaultException<string>( 
8.            string.Format("There is no user with the userName '{0}'.", name), 
9.            HttpStatusCode.NotFound); 
10.     else 
11.         return user; 
12. } 

//当查不到User时，抛出WebFaultException，并提示NotFound及错误信息[WebGet(UriTemplate="/Users/{name}")]public User GetUser(string name){ var user = Users.FirstOrDefault(u => u.Name == name); if (user == null) throw new WebFaultException<string>( string.Format("There is no user with the userName '{0}'.", name), HttpStatusCode.NotFound); else return user;}
客户端代码：
1. 先包装 HttpWebRequest 的Get方法便于演示：

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1. static string RequestGet(string url) 
2. { 
3.     var req = HttpWebRequest.Create(url); 
4.     using (var resp = req.GetResponse()) 
5.     { 
6.         using (var stream = resp.GetResponseStream()) 
7.         { 
8.             using (var sr = new StreamReader(stream)) 
9.             { 
10.                 return sr.ReadToEnd(); 
11.             } 
12.         } 
13.     } 
14. } 

static string RequestGet(string url){ var req = HttpWebRequest.Create(url); using (var resp = req.GetResponse()) { using (var stream = resp.GetResponseStream()) { using (var sr = new StreamReader(stream)) { return sr.ReadToEnd(); } } }}
2. 客户端请求REST服务，这里传给服务端一个错误名字:errorname，服务端查不到抛出异常。

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1. var resp = RequestGet("http://localhost:52402/Service1/Users/errorname"); 
2. Console.WriteLine(resp); 

var resp = RequestGet("http://localhost:52402/Service1/Users/errorname");Console.WriteLine(resp);
3. 当Response.StatusCode 不等于 200(成功) 的时候，GetResponse() 方法会抛出 WebException，我们通过捕获它获得异常的详细内容：(WebException.Response 可以获得出错时的Response，服务端的错误内容写在Response Body里)

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1. try 
2. { 
3.     // Request ... 
4. } 
5. catch (WebException ex) 
6. { 
7.     var errResp = ex.Response as HttpWebResponse; 
8.     Console.WriteLine("StatusCode:{0}({1})", errResp.StatusCode, (int)errResp.StatusCode); 
9.     using (var stream = errResp.GetResponseStream()) 
10.     { 
11.         using (var sr = new StreamReader(stream)) 
12.         { 
13.             Console.WriteLine("Content:{0}", sr.ReadToEnd()); 
14.         } 
15.     } 
16. } 

try{ // Request ...}catch (WebException ex){ var errResp = ex.Response as HttpWebResponse; Console.WriteLine("StatusCode:{0}({1})", errResp.StatusCode, (int)errResp.StatusCode); using (var stream = errResp.GetResponseStream()) { using (var sr = new StreamReader(stream)) { Console.WriteLine("Content:{0}", sr.ReadToEnd()); } }}
运行结果：


WebFaultException<T> 还支持返回复杂的“错误”对象，我们在服务端定义一个复杂的错误类：

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1. public class ComplexError 
2. { 
3.     public string ErrorCode {get; set; } 
4.     public string ErrorMessage {get; set; } 
5. } 

public class ComplexError{ public string ErrorCode { get; set; } public string ErrorMessage { get; set; }}
在服务中抛出这个复杂错误：

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1. [WebGet(UriTemplate = "/Users2/{name}")] 
2. public User GetUser2(string name) 
3. { 
4.     var user = Users.FirstOrDefault(u => u.Name == name); 
5.     if (user == null) 
6.         throw new WebFaultException<ComplexError>( 
7.            new ComplexError 
8.            { 
9.                ErrorCode = "E001", 
10.                ErrorMessage = string.Format("There is no user with the userName '{0}'.", name) 
11.            }, 
12.            HttpStatusCode.NotFound); 
13.     else 
14.         return user; 
15. } 

[WebGet(UriTemplate = "/Users2/{name}")]public User GetUser2(string name){ var user = Users.FirstOrDefault(u => u.Name == name); if (user == null) throw new WebFaultException<ComplexError>( new ComplexError { ErrorCode = "E001", ErrorMessage = string.Format("There is no user with the userName '{0}'.", name) }, HttpStatusCode.NotFound); else return user;}
服务端会按照既定的ResponseFormat返回错误信息。
运行结果：


PS: 如果使用 WCF REST Starter Kit 的 HttpClient 处理的话，需要自己判断 StatusCode。

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1. var client = new HttpClient(); 
2. var resp = client.Get("http://localhost:52402/Service1/Users/errorname"); 
3. Console.WriteLine("StatusCode:{0}({1})", resp.StatusCode, (int)resp.StatusCode); 
4. var result = resp.Content.ReadAsString(); 
5. Console.WriteLine("Content:{0}", result);