C#以post方式调用struts rest-plugin service的问题

struts2: 玩转 rest-plugin 一文中，学习了用struts2开发restful service的方法，发现用c#以post方式调用时各种报错，但java、ajax，包括firefox 的rest client插件测试也无问题。

先给出rest service中的这个方法：

 1     // POST /orders
 2     public HttpHeaders create() throws IOException, ServletException {
 3         ordersService.doSave(model);
 4         HttpServletResponse response = ServletActionContext.getResponse();
 5         HttpServletRequest request = ServletActionContext.getRequest();
 6         String ContentType = request.getHeader("Content-Type").toLowerCase();
 7         if (ContentType.startsWith("application/xml")) { // 返回xml视图
 8             response.sendRedirect("orders/" + model.getId() + ".xml");
 9         } else if (ContentType.startsWith("application/json")) { // 返回json视图
10             response.sendRedirect("orders/" + model.getId() + ".json");
11         } else {// 返回xhtml页面视图
12             response.sendRedirect("orders/");
13         }
14         return null;
15     }

代码不复杂，post一段String过来(xml/json/html格式均可)，自动映射成Order对象的实例model，然后根据请求HttpHeader中的Content-Type，如果是xml(application/xml)，则返回model对应的xml，如果是json(application/json)，则返回model对应的json，其它则返回页面

c#的调用代码：

 1 static string PostDataByWebClient(String postUrl, String paramData, String mediaType)
 2 {
 3     String result = String.Empty;
 4     try
 5     {
 6         byte[] postData = Encoding.UTF8.GetBytes(paramData);
 7         WebClient webClient = new WebClient();
 8         webClient.Headers.Add("Content-Type", mediaType);
 9         byte[] responseData = webClient.UploadData(new Uri(postUrl), "POST", postData);
10         result = Encoding.UTF8.GetString(responseData);
11     }
12     catch (Exception e)
13     {
14         Console.WriteLine(e);
15         result = e.Message;
16     }
17     return result;
18 }
19 
20 static string PostDataByWebRequest(string postUrl, string paramData, String mediaType)
21 {
22     string result = string.Empty;
23     Stream newStream = null;
24     StreamReader sr = null;
25     HttpWebResponse response = null;
26     try
27     {
28         byte[] byteArray = Encoding.UTF8.GetBytes(paramData);
29         HttpWebRequest webReq = (HttpWebRequest)WebRequest.Create(new Uri(postUrl));
30         webReq.Method = "POST";
31         webReq.ContentType = mediaType;
32         webReq.ContentLength = byteArray.Length;
33         newStream = webReq.GetRequestStream();
34         newStream.Write(byteArray, 0, byteArray.Length);
35         response = (HttpWebResponse)webReq.GetResponse();
36         sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
37         result = sr.ReadToEnd();
38     }
39     catch (Exception ex)
40     {
41         Console.WriteLine(ex);
42         result = ex.Message;
43     }
44     finally
45     {
46         if (sr != null)
47         {
48             sr.Close();
49         }
50         if (response != null)
51         {
52             response.Close();
53         }
54         if (newStream != null)
55         {
56             newStream.Close();
57         }
58     }
59     return result;
60 }

这二种常用的调用方式，居然全跪了，返回的结果是一堆java异常：  java.lang.NullPointerException         at org.apache.struts2.convention.ConventionUnknownHandler.handleUnknownActionMethod(ConventionUnknownHandler.java:423)         at com.opensymphony.xwork2.DefaultUnknownHandlerManager.handleUnknownMethod(DefaultUnknownHandlerManager.java:96)

...

无奈百度了一圈，发现还有另一种方法，利用TcpClient调用

 1 static string PostDataByTcpClient(string postUrl, string paramData, String mediaType)
 2 {
 3     String result = String.Empty;
 4     TcpClient clientSocket = null;
 5     Stream readStream = null;
 6     try
 7     {
 8         clientSocket = new TcpClient();
 9         Uri URI = new Uri(postUrl);
10         clientSocket.Connect(URI.Host, URI.Port);
11         StringBuilder RequestHeaders = new StringBuilder();//用来保存HTML协议头部信息
12         RequestHeaders.AppendFormat("{0} {1} HTTP/1.1rn", "POST", URI.PathAndQuery);
13         RequestHeaders.AppendFormat("Connection:closern");
14         RequestHeaders.AppendFormat("Host:{0}:{1}rn", URI.Host,URI.Port);
15         RequestHeaders.AppendFormat("Content-Type:{0}rn", mediaType);
16         RequestHeaders.AppendFormat("rn");
17         RequestHeaders.Append(paramData + "rn");
18         Encoding encoding = Encoding.UTF8;
19         byte[] request = encoding.GetBytes(RequestHeaders.ToString());
20         clientSocket.Client.Send(request);
21         readStream = clientSocket.GetStream();
22         StreamReader sr = new StreamReader(readStream, Encoding.UTF8);
23         result = sr.ReadToEnd();
24     }
25     catch (Exception e)
26     {
27         Console.WriteLine(e);
28         result = e.Message;
29     }
30     finally
31     {
32         if (readStream != null)
33         {
34             readStream.Close();
35         }
36         if (clientSocket != null)
37         {
38             clientSocket.Close();
39         }
40     }
41     return result;
42 }

总算调用成功了，但是由于java端是用SendRedirect在客户端重定向的，所以该方法得到的返回结果如下：

HTTP/1.1 302 Found Server: Apache-Coyote/1.1 Location: http://localhost:8080/struts2-rest-ex/rest/orders/230.xml Content-Length: 0 Date: Mon, 27 Oct 2014 03:18:56 GMT Connection: close

是一堆http头的原文，只能曲线救国，将其中的Location:后的部分（即重定向的url），取出来再次get请求。

这样的解决方案显然有点笨拙，继续深挖：

org.apache.struts2.rest.RestActionMapper这个类的getMapping()方法，看下源码：

  1     public ActionMapping getMapping(HttpServletRequest request,
  2             ConfigurationManager configManager) {
  3         ActionMapping mapping = new ActionMapping();
  4         String uri = RequestUtils.getUri(request);
  5 
  6         uri = dropExtension(uri, mapping);
  7         if (uri == null) {
  8             return null;
  9         }
 10 
 11         parseNameAndNamespace(uri, mapping, configManager);
 12 
 13         handleSpecialParameters(request, mapping);
 14 
 15         if (mapping.getName() == null) {
 16             return null;
 17         }
 18 
 19         // handle "name!method" convention.
 20         handleDynamicMethodInvocation(mapping, mapping.getName());
 21 
 22         String fullName = mapping.getName();
 23         // Only try something if the action name is specified
 24         if (fullName != null && fullName.length() > 0) {
 25 
 26             // cut off any ;jsessionid= type appendix but allow the rails-like ;edit
 27             int scPos = fullName.indexOf(';');
 28             if (scPos > -1 && !"edit".equals(fullName.substring(scPos + 1))) {
 29                 fullName = fullName.substring(0, scPos);
 30             }
 31 
 32             int lastSlashPos = fullName.lastIndexOf('/');
 33             String id = null;
 34             if (lastSlashPos > -1) {
 35 
 36                 // fun trickery to parse 'actionName/id/methodName' in the case of 'animals/dog/edit'
 37                 int prevSlashPos = fullName.lastIndexOf('/', lastSlashPos - 1);
 38                 if (prevSlashPos > -1) {
 39                     mapping.setMethod(fullName.substring(lastSlashPos + 1));
 40                     fullName = fullName.substring(0, lastSlashPos);
 41                     lastSlashPos = prevSlashPos;
 42                 }
 43                 id = fullName.substring(lastSlashPos + 1);
 44             }
 45 
 46 
 47 
 48             // If a method hasn't been explicitly named, try to guess using ReST-style patterns
 49             if (mapping.getMethod() == null) {
 50 
 51                 if (isOptions(request)) {
 52                     mapping.setMethod(optionsMethodName);
 53                 
 54                 // Handle uris with no id, possibly ending in '/'
 55                 } else if (lastSlashPos == -1 || lastSlashPos == fullName.length() -1) {
 56 
 57                     // Index e.g. foo
 58                     if (isGet(request)) {
 59                         mapping.setMethod(indexMethodName);
 60                         
 61                     // Creating a new entry on POST e.g. foo
 62                     } else if (isPost(request)) {
 63                         if (isExpectContinue(request)) {
 64                             mapping.setMethod(postContinueMethodName);
 65                         } else {
 66                             mapping.setMethod(postMethodName);
 67                         }
 68                     }
 69 
 70                 // Handle uris with an id at the end
 71                 } else if (id != null) {
 72                     
 73                     // Viewing the form to edit an item e.g. foo/1;edit
 74                     if (isGet(request) && id.endsWith(";edit")) {
 75                         id = id.substring(0, id.length() - ";edit".length());
 76                         mapping.setMethod(editMethodName);
 77                         
 78                     // Viewing the form to create a new item e.g. foo/new
 79                     } else if (isGet(request) && "new".equals(id)) {
 80                         mapping.setMethod(newMethodName);
 81 
 82                     // Removing an item e.g. foo/1
 83                     } else if (isDelete(request)) {
 84                         mapping.setMethod(deleteMethodName);
 85                         
 86                     // Viewing an item e.g. foo/1
 87                     } else if (isGet(request)) {
 88                         mapping.setMethod(getMethodName);
 89                     
 90                     // Updating an item e.g. foo/1    
 91                     }  else if (isPut(request)) {
 92                         if (isExpectContinue(request)) {
 93                             mapping.setMethod(putContinueMethodName);
 94                         } else {
 95                             mapping.setMethod(putMethodName);
 96                         }
 97                     }
 98                 }
 99             }
100 
101             // cut off the id parameter, even if a method is specified
102             if (id != null) {
103                 if (!"new".equals(id)) {
104                     if (mapping.getParams() == null) {
105                         mapping.setParams(new HashMap());
106                     }
107                     mapping.getParams().put(idParameterName, new String[]{id});
108                 }
109                 fullName = fullName.substring(0, lastSlashPos);
110             }
111 
112             mapping.setName(fullName);
113             return mapping;
114         }
115         // if action name isn't specified, it can be a normal request, to static resource, return null to allow handle that case
116         return null;
117     }

注意91-96行，这里有一个判断：

1                     }  else if (isPut(request)) {
2                         if (isExpectContinue(request)) {
3                             mapping.setMethod(putContinueMethodName);
4                         } else {
5                             mapping.setMethod(putMethodName);
6                         }
7                     }

再来细看下：isExpectContinue

1     protected boolean isExpectContinue(HttpServletRequest request) {
2         String expect = request.getHeader("Expect");
3         return (expect != null && expect.toLowerCase().contains("100-continue")); 
4     }

这段代码的意思是如果请求Http头里有Except信息，且等于100-continue，则返回true。如果返回true，刚才那段判断，会返回putContinueMethodName这个变量所指的方法：

1  private String postContinueMethodName = "createContinue";

但是Controller里只有create方法，并没有createContinue方法，所以找不到方法，当然报错。

而c#中如果以post方法请求url时，不论是HttpWebRequest还是WebClient，默认都会添加expect = 100-continue的头信息，因此c#调用时会报错，而firefox的RestClient插件、java调用、ajax调用，因为没有拼except信息，不会出错。

那么except = 100-continue是什么东西呢？为何c#要自动拼这上这行头信息？可以参见园友的文章：http之100-continue，大意是说：

如果客户端向服务端post数据，考虑到post的数据可能很大，搞不好能把服务器玩坏（或者超时），所以，有一个贴心的约定，客户端先发一个except头信息给服务器，问下：我要post数据了，可能很大，你想想要不要收，采用什么措施收？如果服务器很聪明，可能会对这种情况做出特殊响应，就比如刚才的java代码，遇到这种头信息，不是调用create方法，而是createContinue方法。

这本是一个不错的约定，但是偏偏本文中的Controller方法，又没有提供createContinue方法，所以辜负了客户端的美意，好心当成驴肝肺了。

终极解决方案：

方案A：HttpWebRequest请求时，把默认的except行为去掉

1 webReq.ServicePoint.Expect100Continue = false;//禁止自动添加Except:100-continue到http头信息

这样，最终发出去的头信息，就不会有except行

方案B: Controller中把createContinue方法补上

1     public HttpHeaders createContinue() throws IOException, ServletException{
2         return create();
3     }

直接调用create方法，安抚下双方，不让调用出错即可。