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。