HTTP and XMLHTTP status code Overview

(1) status code supported by HTTP 1.1
　　
100 the initial request for continue has been accepted, and the customer shall continue to send the rest of the request
　　
101 The switching protocols server converts a client-compliant request to another protocol
　　
200 OK everything is normal, and the response document to the get and post requests follows.
　　
The 201 created server has created a document and the location header provides its URL.
　　
202 accepted has accepted the request, but the processing has not been completed.
　　
203 the non-authoritative information document has been normally returned, but some response headers may be incorrect because the document copy is used.
　　
204 NO content does not have a new document. The browser should continue to display the original document. This status code is useful if the user regularly refreshes the page and the servlet can determine that the user document is new enough.
　　
205 there is no new content in the reset content, but the browser should reset the content displayed by it. Used to force the browser to clear the input content of the form
　　
206 partial content the client sent a GET request with the range header, and the server completed it.
　　
300 the documents requested by the multiple choices client can be found in multiple locations, which are listed in the returned documents. If the server needs to give priority, it should be specified in the location response header.
　　
301 moved permanently the document requested by the customer is elsewhere. The new URL is provided in the location header and the browser should automatically access the new URL.
　　
302 found is similar to 301, but the new URL should be treated as a temporary alternative, rather than permanent.
　　
303 see other is similar to 301/302. The difference is that if the original request is post, the redirection target document specified by the location header should be extracted through get
　　
304 The not modified client has a buffered document and issued a conditional request (generally, the IF-modified-since header is provided to indicate that the customer only wants to update the document on a specified date ). The server tells the customer that the original buffer documentation can still be used.
　　
305 the document requested by the use proxy client should be extracted from the proxy server specified by the location header
　　
307 temporary redirect and 302 (found) are the same. Many browsers mistakenly respond to the 302 response for redirection. Even if the original request is post, it can only be redirected when the POST request actually responds to 303. For this reason, HTTP 1.1 adds 307 to clear the region code in several states: When a 303 response occurs, the browser can follow the redirected get and post requests; if a 307 response occurs, the browser can only follow the redirection to get requests.
　　
400 syntax error in bad request.
　　
401 unauthorized the customer attempted to access the password-protected page without authorization. The response contains a WWW-Authenticate header. the browser displays the username/password dialog box accordingly, and then sends a request again after entering the appropriate authorization header.
　　
403 Forbidden resources are unavailable.
　　
404 Not found cannot find the resource at the specified position
　　
405 method not allowed request methods (get, post, Head, delete, put, Trace, etc.) are not applicable to specified resources.
　　
406 the resource specified by not acceptable has been found, but its MIME type is incompatible with the one specified by the customer in the accpet header.
　　
407 proxy authentication required is similar to 401, indicating that the customer must first be authorized by the proxy server.
　　
408 request timeout the client has not sent any request within the waiting time permitted by the server. The customer can repeat the same request later.
　　
409 conflict is usually related to put requests. The request cannot be successful because the request conflicts with the current status of the resource.
　　
410 the document requested by gone is no longer available, and the server does not know which address to redirect. It differs from 404 in that if 407 is returned, the document permanently leaves the specified position, and 404 indicates that the document is unavailable for unknown reasons.
　　
The 411 length required server cannot process the request unless the customer sends a Content-Length header.
　　
412 precondition failed: Some of the prerequisites specified in the request header fail.
　　
413 the size of the target Request Entity too large document exceeds the size that the server is willing to process. If the server thinks it can process the request later, it should provide a retry-after Header
　　
414 request URI Too long URI is too long
　　
416 the requested range not satisfiable server cannot meet the range header specified by the customer in the request.
　　
500 the internal server error server encounters unexpected circumstances and cannot complete the customer's request
　　
501 The not implemented server does not support the functions required to implement the request. For example, the customer sends a put request not supported by the server.
　　
502 when the Bad Gateway server acts as a gateway or proxy, in order to complete the request to access the next server, but the server returns an INVALID RESPONSE
　　
503 the service unavailable server fails to respond due to maintenance or overload. For example, Servlet may return 503 when the database connection pool is full. A retry-after header can be provided when the server returns 503
　　
504 gateway timeout is used by a proxy or gateway server, indicating that the remote server cannot receive a response in a timely manner.
　　
505 the HTTP Version Not Supported server does not support the HTTP Version specified in the request
　　
(2) XMLHTTPRequest object Method
　　
Abort () stops the current request
GetAllResponseHeaders () is used as a string to return to the complete headers.
GetResponseHeader ("headerlabel") returns a single header label as a string
Open ("method", "url" [, asyncflag [, "username" [, "password"]) sets the target URL, method, and other parameters of a pending request.
Send (content) Send request
SetRequestHeader ("label", "value") sets the header and sends it together with the request
　　
(3) XMLHTTPRequest object attributes
　　
Onreadystatechange event trigger
Readystate object status (integer ):
0 = not initialized
1 = reading
2 = read
3 = interaction in progress
4 = complete
The text version of the data returned by the responsetext server process
Responsexml: XML Document Object compatible with Dom returned by the server process
Status Code returned by the Status server, for example, 404 = "found at the end of the file", 200 = "successful"
Status text returned by the statustext Server