struts2: 玩轉 rest-plugin 一文中，學習了用struts2開發restful service的方法，發現用c#以post方式調用時各種報錯，但java、ajax，包括firefox 的rest client插件測試也無問題。

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先給出rest service中的這個方法：

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視圖 8 response.sendRedirect("orders/" + model.getId() + ".xml"); 9 } else if (ContentType.startsWith("application/json")) { // 返回json視圖 10 response.sendRedirect("orders/" + model.getId() + ".json"); 11 } else {// 返回xhtml頁面視圖 12 response.sendRedirect("orders/"); 13 } 14 return null; 15 } View Code

代碼不復雜，post一段String過來(xml/json/html格式均可)，自動映射成Order對象的實例model，然后根據請求HttpHeader中的Content-Type，如果是xml(application/xml)，則返回model對應的xml，如果是json(application/json)，則返回model對應的json，其它則返回頁面

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c#的調用代碼：

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 } View Code

這二種常用的調用方式，居然全跪了，返回的結果是一堆java異常：
?java.lang.NullPointerException
??????? at org.apache.struts2.convention.ConventionUnknownHandler.handleUnknownActionMethod(ConventionUnknownHandler.java:423)
??????? at com.opensymphony.xwork2.DefaultUnknownHandlerManager.handleUnknownMethod(DefaultUnknownHandlerManager.java:96)

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無奈百度了一圈，發現還有另一種方法，利用TcpClient調用

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();//用來保存HTML協議頭部信息 12 RequestHeaders.AppendFormat("{0} {1} HTTP/1.1\r\n", "POST", URI.PathAndQuery); 13 RequestHeaders.AppendFormat("Connection:close\r\n"); 14 RequestHeaders.AppendFormat("Host:{0}:{1}\r\n", URI.Host,URI.Port); 15 RequestHeaders.AppendFormat("Content-Type:{0}\r\n", mediaType); 16 RequestHeaders.AppendFormat("\r\n"); 17 RequestHeaders.Append(paramData + "\r\n"); 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 } View Code

總算調用成功了，但是由于java端是用SendRedirect在客戶端重定向的，所以該方法得到的返回結果如下：

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頭的原文，只能曲線救國，將其中的Location:后的部分（即重定向的url），取出來再次get請求。

這樣的解決方案顯然有點笨拙，繼續深挖：

org.apache.struts2.rest.RestActionMapper這個類的getMapping()方法，看下源碼：

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 } View Code

注意91-96行，這里有一個判斷：

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

再來細看下：isExpectContinue

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

這段代碼的意思是如果請求Http頭里有Except信息，且等于100-continue，則返回true。如果返回true，剛才那段判斷，會返回putContinueMethodName這個變量所指的方法：

1 private String postContinueMethodName = "createContinue";

但是Controller里只有create方法，并沒有createContinue方法，所以找不到方法，當然報錯。

而c#中如果以post方法請求url時，不論是HttpWebRequest還是WebClient，默認都會添加expect = 100-continue的頭信息，因此c#調用時會報錯，而firefox的RestClient插件、java調用、ajax調用，因為沒有拼except信息，不會出錯。

那么except = 100-continue是什么東西呢？為何c#要自動拼這上這行頭信息？可以參見園友的文章：http之100-continue，大意是說：

如果客戶端向服務端post數據，考慮到post的數據可能很大，搞不好能把服務器玩壞（或者超時），所以，有一個貼心的約定，客戶端先發一個except頭信息給服務器，問下：我要post數據了，可能很大，你想想要不要收，采用什么措施收？如果服務器很聰明，可能會對這種情況做出特殊響應，就比如剛才的java代碼，遇到這種頭信息，不是調用create方法，而是createContinue方法。

這本是一個不錯的約定，但是偏偏本文中的Controller方法，又沒有提供createContinue方法，所以辜負了客戶端的美意，好心當成驢肝肺了。

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終極解決方案：

方案A：HttpWebRequest請求時，把默認的except行為去掉

1 webReq.ServicePoint.Expect100Continue = false;//禁止自動添加Except:100-continue到http頭信息

這樣，最終發出去的頭信息，就不會有except行

方案B: Controller中把createContinue方法補上

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

直接調用create方法，安撫下雙方，不讓調用出錯即可。

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