HTTP status Code

502 Bad Gateway:tomcat didn't start up.
504 Gateway Time-out:nginx reported errors, usually nginx as a reverse proxy server, the connected application server such as Tomcat did not cause the corresponding

302 (Temporary move) The server is currently responding to a request from a Web page in a different location, but the requestor should continue to use the original location for subsequent requests, and when 302 responds, the temporary URL is returned to the client through the site field.
304 (not modified) The requested webpage has not been modified since the last request. When the server returns this response, the Web page content is not returned.
307-temporary Redirect Many browsers incorrectly respond with a 302 response for redirection, even if the original request is post,even if it can actually be redirected only if the answer to the POST request is 303。 For this reason, HTTP 1.1 has been added 307 to allow for more cleanup of the region in several status codes:When a 303 response occurs, the browser can follow the redirected get and post requests, and if the 307,301,302 answer, the browser can only follow the redirect to the request. (HTTP 1.1 new)

According to the RFC2616D definition, for HTTP response Response Codes 301, 302, 307, if the request is not a get or head, and the response returns a status code of 302, then the browser prohibits redirection to the new request unless the user confirms it! This can occur because of a request condition change. Reference:RFC2616 Hypertext Transfer Protocol--http/1.1
The corresponding Java HTTP client package is handled according to this specification, if the return response status code is 307,301,302 of the POST request settings setfollowredirects, The system will error: Java.lang.IllegalArgumentException:Entity enclosing requests cannot be redirected without user intervention! If you can, change post to get and automatically redirect even in case of 307 response code

1xx response information hint
These status codes represent a temporary response. The client should be prepared to receive one or more 1xx before receiving a regular response
? 100-continue the initial request has been accepted, the customer should continue to send the remainder of the request. (HTTP 1.1 new)
? 101-switching Protocols Server translates the client's request to another protocol (HTTP 1.1 new)
2xx-Success
This type of status code indicates that the server successfully accepted the client request.
? 200-okEverything is OK, the answer document for Get and post requests is followed.
? The 201-created server has created the document, and the location header gives its URL.
? 202-accepted has accepted the request, but the processing has not been completed.
? The 203-non-authoritative information document has returned normally, but some of the answer headers may be incorrect because a copy of the document is being used, non-authoritative (HTTP 1.1 new).
? 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 refreshes the page on a regular basis and the servlet can determine that the user's document is new enough.
? 205-reset content is not new, but the browser should reset what it displays. Used to force the browser to clear the form input (HTTP 1.1 new).
? The 206-partial Content client sent a GET request with a range header (block request) and the server completed it (HTTP 1.1 new).
3xx- redirect
The client browser must take more action to implement the request. For example, the browser might have to request a different page on the server, or repeat the request through a proxy server.
? 300-multiple Choices Customer-requested documents can be found in multiple locations that are listed in the returned document. If the server wants to make a preference, it should be indicated in the location answer header.
? 301-moved permanentlyThe document requested by the customer elsewhere, the new URL is given in the location header, and the browser should automatically access the new URL when the request.
The 302-found is similar to 301, but the new URL should be treated as a temporary replacement, not a permanent. Note that the corresponding status information in HTTP1.0 is "Moved temporatily". When the status code appears, the browser can automatically access the new URL, so it is a useful status code. Note that this status code can sometimes be used with 301 substitutions. For example, if the browser mistakenly requests Http://host/~user (the trailing slash is missing), some servers return 301, and some return 302. Strictly speaking,we can only assume that the browser will automatically redirect only if the original request is. See 307.
? 303-see other is similar to 301/302, except that if the original request is a post,location header the specified redirect target document should be fetched through get,that is, the main meaning of the status code is to handle the case where the POST request is redirected to the GET request(HTTP 1.1 new).
? 304-not ModifiedThe client has a buffered document and issues a conditional request (typically providing a if-modified-since header indicating that the customer only wants to update the document than the specified date). The server tells the customer that the original buffered document can continue to be used.
? 305-use Proxy The document requested by the client should be extracted via the proxy server indicated by the location header (HTTP 1.1 is new).
? 307-temporary Redirect Many browsers incorrectly respond to a 302 response for redirection,even if the original request is post, it can only be redirected if it is actually only 303 when the answer to the POST request is. For this reason, HTTP 1.1 has been added 307 to allow for more cleanup of the region in several status codes:When a 303 response occurs, the browser can follow the redirected get and post requests, and if the 307,301,302 answer, the browser can only follow the redirect to the request. (HTTP 1.1 new)
4xx-Client Error
An error occurred and the client appears to be having problems. For example, a client requests a page that does not exist, and the client does not provide valid authentication information.
? 400-bad request syntax error occurred.
? 401-unauthorized access was denied and the customer attempted to access a password-protected page without authorization. A www-authenticate header is included in the answer, and the browser displays the user name/Password dialog box, and then makes a request again after filling in the appropriate authorization header. IIS defines a number of different 401 errors, which indicate a more specific cause of the error. These specific error codes are displayed in the browser, but are not displayed in the IIS log:
? 401.1-Login failed.
? 401.2-The server configuration caused the login to fail.
? 401.3-not authorized due to ACL restrictions on resources.
? 401.4-Filter Authorization failed.
? 401.5-ISAPI/CGI application authorization failed.
? 401.7– access is denied by the URL authorization policy on the WEB server. This error code is specific to IIS 6.0.
The 403-forbidden resource is not available. The server understands the customer's request, but refuses to process it. This is usually caused by the permissions set on the file or directory on the server. Forbidden Access: IIS defines a number of different 403 errors, which indicate a more specific cause of the error:
? 403.1-execution access is forbidden.
? 403.2-Read access is forbidden.
? 403.3-Write access is forbidden.
? 403.4-Requires SSL.
? 403.5-Requires SSL 128.
? The 403.6-IP address is rejected.
? 403.7-Requires a client certificate.
? 403.8-site access is denied.
? 403.9-Excessive number of users.
? 403.10-Invalid configuration.
? 403.11-Password change.
? 403.12-Deny access to the mapping table.
? 403.13-The client certificate is revoked.
? 403.14-Reject directory list.
? 403.15-Client access permission exceeded.
? 403.16-Client certificate is not trusted or invalid.
? 403.17-The client certificate has expired or is not yet valid.
? 403.18-The requested URL cannot be executed in the current application pool. This error code is specific to IIS 6.0.
? 403.19-CGI cannot be executed for clients in this application pool. This error code is specific to IIS 6.0.
? 403.20-passport Login failed. This error code is specific to IIS 6.0.
? 404-not FoundThe resource at the specified location could not be found. This is also a common answer.
? 404.0-(None) – No files or directories found.
? 404.1-Unable to access the WEB site on the requested port.
? The 404.2-web service extension lockout policy blocks this request.
? The 404.3-mime mapping policy blocks this request.
? 405-method not allowed request method (GET, POST, HEAD, DELETE, PUT, trace, etc.) does not apply to the specified resource, the HTTP verb used to access this page is not allowed (the method is not allowed) (HTTP 1.1 new)
? 406-not acceptable The specified resource has been found, but its MIME type is incompatible with the client specified in the Accpet header, the client browser does not accept the MIME type of the requested page (HTTP 1.1 new).
? 407-proxy authentication Required requires proxy authentication, similar to 401, to indicate that the client must be authorized by the proxy server first. (HTTP 1.1 new)
? 408-request Timeout The customer has not made any requests during the waiting time of the server license. Customers can repeat the same request at a later time. (HTTP 1.1 new)
? 409-conflict is usually associated with a put request. The request cannot succeed because the request conflicts with the current state of the resource. (HTTP 1.1 new)
? The document requested by 410-gone is no longer available, and the server does not know which address to redirect to. It differs from 404 in that returning 407 means that the document has permanently left the specified location, and 404 indicates that the document is unavailable for unknown reasons. (HTTP 1.1 new)
? The 411-length Required server cannot process the request unless the client sends a content-length header. (HTTP 1.1 new)
? 412-precondition Failed Some of the prerequisites specified in the request header failed (HTTP 1.1 new).
? 413–request Entity Too Large the size of the target document exceeds the size that the server is currently willing to handle. If the server thinks it can process the request later, it should provide a Retry-after header (HTTP 1.1 new).
? 414-request URI Too Long URI is too lengthy (HTTP 1.1 new).
? 415– media types not supported.
? The 416–requested range not satisfiable server does not meet the Range header specified by the customer in the request. (HTTP 1.1 new)? 417– execution failed.
? 423– a locked error.
5xx-Server error
The server could not complete the request because it encountered an error.
? The 500-internal server Error server encountered unexpected conditions and was unable to complete the client's request.
? 500.12-The application is busy restarting on the WEB server.
? The 500.13-web server is too busy.
? 500.15-Direct Request Global.asa is not allowed.
? 500.16–unc authorization credentials are incorrect. This error code is specific to IIS 6.0.
? The 500.18–url authorization store cannot be opened. This error code is specific to IIS 6.0.
? 500.100-Internal ASP error.
? The 501-not implemented server does not support the functionality required to implement the request, and the header value specifies the configuration that is not implemented. For example, a customer sends a put request that is not supported by the server.
? 502-bad GatewayWhen the server acts as a gateway or proxy, the server returns an illegal response in order to complete the request to access the next server. It also says that the Web server received an invalid response when it was used as a gateway or proxy server.
? The 502.1-cgi application timed out.
? 502.2-CGI Application error.
? 503-service unavailable Service Unavailable, the server failed to answer due to maintenance or heavy load. For example, a servlet might return 503 if the database connection pool is full. A retry-after header can be supplied when the server returns 503. This error code is specific to IIS 6.0.
? 504-gateway Timeout Gateway Timeout, which is used by a server acting as a proxy or gateway, indicating that a reply cannot be received from the remote server in a timely manner. (HTTP 1.1 new).
? The HTTP version indicated in the request is not supported by the 505-HTTP version not supported server. (HTTP 1.1 new)

HTTP status Code