The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If the Request-URI refers to an already existing resource, the enclosed entity SHOULD be considered as a modified version of the one residing on the origin server. If the Request-URI does not point to an existing resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create the resource with that URI. If a new resource is created, the origin server MUST inform the user agent via the 201 (Created) response. If an existing resource is modified, either the 200 (OK) or 204 (No Content) response codes SHOULD be sent to indicate successful completion of the request. If the resource could not be created or modified with the Request-URI, an appropriate error response SHOULD be given that reflects the nature of the problem. The recipient of the entity MUST NOT ignore any Content-* (e.g. Content-Range) headers that it does not understand or implement and MUST return a 501 (Not Implemented) response in such cases.

If the request passes through a cache and the Request-URI identifies one or more currently cached entities, those entries SHOULD be treated as stale. Responses to this method are not cacheable.

The fundamental difference between the POST and PUT requests is reflected in the different meaning of the Request-URI. The URI in a POST request identifies the resource that will handle the enclosed entity. That resource might be a data-accepting process, a gateway to some other protocol, or a separate entity that accepts annotations. In contrast, the URI in a PUT request identifies the entity enclosed with the request -- the user agent knows what URI is intended and the server MUST NOT attempt to apply the request to some other resource. If the server desires that the request be applied to a different URI,

it MUST send a 301 (Moved Permanently) response; the user agent MAY then make its own decision regarding whether or not to redirect the request.

A single resource MAY be identified by many different URIs. For example, an article might have a URI for identifying "the current version" which is separate from the URI identifying each particular version. In this case, a PUT request on a general URI might result in several other URIs being defined by the origin server.

HTTP/1.1 does not define how a PUT method affects the state of an origin server.

PUT requests MUST obey the message transmission requirements set out in section 8.2.

Unless otherwise specified for a particular entity-header, the entity-headers in the PUT request SHOULD be applied to the resource created or modified by the PUT.

上面说的都是虚的，实战才是硬道理！

• 首先，我们要让Web Server支持Delete 和 Put请求方法，以大家熟悉的Tomcat为例：

在Tomcat的web.xml 文件中配置 org.apache.catalina.servlets.DefaultServlet 的初始化参数

readonly参数默认是true，即不允许delete和put操作，所以默认的通过XMLHttpRequest对象的put或者delete方法访问就会报告 http 403 forbidden 错误。

• 接下来，从客户端通过 Ajax XMLHTTPRequest 发起 DELETE/PUT 请求：
  [javascript] view plain copy

  1. function getXMLHTTPRequest(){
  2. if (XMLHttpRequest)    {
  3. return new XMLHttpRequest();
  4. } else {
  5. try{
  6. return new ActiveXObject('Msxml2.XMLHTTP');
  7. }catch(e){
  8. return new ActiveXObject('Microsoft.XMLHTTP');
  9. }
  10. }
  11. }
  12. var req = getXMLHTTPRequest();
  13. req.open('DELETE','http://localhost/test.jsp',false);
  14. req.send(null);
  15. document.write(req.responseText);
• WebDAV也需要使用到这2种Http请求方法。