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：

     // POST /orders
     public HttpHeaders create() throws IOException, ServletException {
         ordersService.doSave(model);
         HttpServletResponse response = ServletActionContext.getResponse();
         HttpServletRequest request = ServletActionContext.getRequest();
         String ContentType = request.getHeader("Content-Type").toLowerCase();
         if (ContentType.startsWith("application/xml")) { // 返回xml视图
             response.sendRedirect("orders/" + model.getId() + ".xml");
         } else if (ContentType.startsWith("application/json")) { // 返回json视图
             response.sendRedirect("orders/" + model.getId() + ".json");
         } else {// 返回xhtml页面视图
             response.sendRedirect("orders/");
         }
         return null;
     }

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：

 static string PostDataByWebClient(String postUrl, String paramData, String mediaType)
 {
     String result = String.Empty;
     try
     {
         byte[] postData = Encoding.UTF8.GetBytes(paramData);
         WebClient webClient = new WebClient();
         webClient.Headers.Add("Content-Type", mediaType);
         byte[] responseData = webClient.UploadData(new Uri(postUrl), "POST", postData);
         result = Encoding.UTF8.GetString(responseData);
     }
     catch (Exception e)
     {
         Console.WriteLine(e);
         result = e.Message;
     }
     return result;
 }
 
 static string PostDataByWebRequest(string postUrl, string paramData, String mediaType)
 {
     string result = string.Empty;
     Stream newStream = null;
     StreamReader sr = null;
     HttpWebResponse response = null;
     try
     {
         byte[] byteArray = Encoding.UTF8.GetBytes(paramData);
         HttpWebRequest webReq = (HttpWebRequest)WebRequest.Create(new Uri(postUrl));
         webReq.Method = "POST";
         webReq.ContentType = mediaType;
         webReq.ContentLength = byteArray.Length;
         newStream = webReq.GetRequestStream();
         newStream.Write(byteArray, , byteArray.Length);
         response = (HttpWebResponse)webReq.GetResponse();
         sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
         result = sr.ReadToEnd();
     }
     catch (Exception ex)
     {
         Console.WriteLine(ex);
         result = ex.Message;
     }
     finally
     {
         if (sr != null)
         {
             sr.Close();
         }
         if (response != null)
         {
             response.Close();
         }
         if (newStream != null)
         {
             newStream.Close();
         }
     }
     return result;
 }

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

 static string PostDataByTcpClient(string postUrl, string paramData, String mediaType)
 {
     String result = String.Empty;
     TcpClient clientSocket = null;
     Stream readStream = null;
     try
     {
         clientSocket = new TcpClient();
         Uri URI = new Uri(postUrl);
         clientSocket.Connect(URI.Host, URI.Port);
         StringBuilder RequestHeaders = new StringBuilder();//用来保存HTML协议头部信息
         RequestHeaders.AppendFormat("{0} {1} HTTP/1.1\r\n", "POST", URI.PathAndQuery);
         RequestHeaders.AppendFormat("Connection:close\r\n");
         RequestHeaders.AppendFormat("Host:{0}:{1}\r\n", URI.Host,URI.Port);
         RequestHeaders.AppendFormat("Content-Type:{0}\r\n", mediaType);
         RequestHeaders.AppendFormat("\r\n");
         RequestHeaders.Append(paramData + "\r\n");
         Encoding encoding = Encoding.UTF8;
         byte[] request = encoding.GetBytes(RequestHeaders.ToString());
         clientSocket.Client.Send(request);
         readStream = clientSocket.GetStream();
         StreamReader sr = new StreamReader(readStream, Encoding.UTF8);
         result = sr.ReadToEnd();
     }
     catch (Exception e)
     {
         Console.WriteLine(e);
         result = e.Message;
     }
     finally
     {
         if (readStream != null)
         {
             readStream.Close();
         }
         if (clientSocket != null)
         {
             clientSocket.Close();
         }
     }
     return result;
 }

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：

     public ActionMapping getMapping(HttpServletRequest request,
             ConfigurationManager configManager) {
         ActionMapping mapping = new ActionMapping();
         String uri = RequestUtils.getUri(request);
 
         uri = dropExtension(uri, mapping);
         if (uri == null) {
             return null;
         }
 
         parseNameAndNamespace(uri, mapping, configManager);
 
         handleSpecialParameters(request, mapping);
 
         if (mapping.getName() == null) {
             return null;
         }
 
         // handle "name!method" convention.
         handleDynamicMethodInvocation(mapping, mapping.getName());
 
         String fullName = mapping.getName();
         // Only try something if the action name is specified
         if (fullName != null && fullName.length() > 0) {
 
             // cut off any ;jsessionid= type appendix but allow the rails-like ;edit
             int scPos = fullName.indexOf(';');
             if (scPos > -1 && !"edit".equals(fullName.substring(scPos + 1))) {
                 fullName = fullName.substring(0, scPos);
             }
 
             int lastSlashPos = fullName.lastIndexOf('/');
             String id = null;
             if (lastSlashPos > -1) {
 
                 // fun trickery to parse 'actionName/id/methodName' in the case of 'animals/dog/edit'
                 int prevSlashPos = fullName.lastIndexOf('/', lastSlashPos - 1);
                 if (prevSlashPos > -1) {
                     mapping.setMethod(fullName.substring(lastSlashPos + 1));
                     fullName = fullName.substring(0, lastSlashPos);
                     lastSlashPos = prevSlashPos;
                 }
                 id = fullName.substring(lastSlashPos + 1);
             }
 
             // If a method hasn't been explicitly named, try to guess using ReST-style patterns
             if (mapping.getMethod() == null) {
 
                 if (isOptions(request)) {
                     mapping.setMethod(optionsMethodName);
 
                 // Handle uris with no id, possibly ending in '/'
                 } else if (lastSlashPos == -1 || lastSlashPos == fullName.length() -1) {
 
                     // Index e.g. foo
                     if (isGet(request)) {
                         mapping.setMethod(indexMethodName);
 
                     // Creating a new entry on POST e.g. foo
                     } else if (isPost(request)) {
                         if (isExpectContinue(request)) {
                             mapping.setMethod(postContinueMethodName);
                         } else {
                             mapping.setMethod(postMethodName);
                         }
                     }
 
                 // Handle uris with an id at the end
                 } else if (id != null) {
 
                     // Viewing the form to edit an item e.g. foo/1;edit
                     if (isGet(request) && id.endsWith(";edit")) {
                         id = id.substring(0, id.length() - ";edit".length());
                         mapping.setMethod(editMethodName);
 
                     // Viewing the form to create a new item e.g. foo/new
                     } else if (isGet(request) && "new".equals(id)) {
                         mapping.setMethod(newMethodName);
 
                     // Removing an item e.g. foo/1
                     } else if (isDelete(request)) {
                         mapping.setMethod(deleteMethodName);
 
                     // Viewing an item e.g. foo/1
                     } else if (isGet(request)) {
                         mapping.setMethod(getMethodName);
 
                     // Updating an item e.g. foo/1
                     }  else if (isPut(request)) {
                         if (isExpectContinue(request)) {
                             mapping.setMethod(putContinueMethodName);
                         } else {
                             mapping.setMethod(putMethodName);
                         }
                     }
                 }
             }
 
             // cut off the id parameter, even if a method is specified
             if (id != null) {
                 if (!"new".equals(id)) {
                     if (mapping.getParams() == null) {
                         mapping.setParams(new HashMap());
                     }
                     mapping.getParams().put(idParameterName, new String[]{id});
                 }
                 fullName = fullName.substring(0, lastSlashPos);
             }
 
             mapping.setName(fullName);
             return mapping;
         }
         // if action name isn't specified, it can be a normal request, to static resource, return null to allow handle that case
         return null;
     }

注意91-96行，这里有一个判断：

                     }  else if (isPut(request)) {
                         if (isExpectContinue(request)) {
                             mapping.setMethod(putContinueMethodName);
                         } else {
                             mapping.setMethod(putMethodName);
                         }
                     }

再来细看下：isExpectContinue

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

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：

  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

 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

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

直接调用create方法，安抚下双方，不让调用出错即可。