Both the machine and the test environment are OK. But an error is reported as soon as it goes online; the possible reasons are summarized as follows:
1 It may be that the server restricts the permission to upload files. After calling the operation and maintenance to open the file upload permission, this error will no longer be reported.
2 Maybe there are many ways to cause this error, the error I encountered was caused by too much data submitted during the post request. Solution: Modify tomcat's configuration file server.xml
3 The server is not turned on;
4 Cross-domain request problems, such as uploading an excel sheet, open FQ to upload, otherwise it will report net::ERR_CONNECTION_RESET