1. Error log

org.springframework.web.multipart.MultipartException: Failed to parse multipart servlet request; nested exception is java.lang.RuntimeException: java.nio.file.NoSuchFileException: /tmp/undertow.8081.6091954911906268442/undertow2435234810596519507upload
        at org.springframework.web.multipart.support.StandardMultipartHttpServletRequest.handleParseFailure(StandardMultipartHttpServletRequest.java:124)
        at org.springframework.web.multipart.support.StandardMultipartHttpServletRequest.parseRequest(StandardMultipartHttpServletRequest.java:115)
        at org.springframework.web.multipart.support.StandardMultipartHttpServletRequest.<init>(StandardMultipartHttpServletRequest.java:88)
        at org.springframework.web.multipart.support.StandardServletMultipartResolver.resolveMultipart(StandardServletMultipartResolver.java:87)
        at org.springframework.web.servlet.DispatcherServlet.checkMultipart(DispatcherServlet.java:1178)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1012)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
        at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)

2. Cause of problem

After consulting the blog, I know the cause of the problem:
in Linux system, when the spring boot application is started with Java jar command, a Tomcat (or undertow) temporary directory will be generated in the/tmp directory of the operating system. The uploaded files must be converted into temporary files and saved under this folder. Because the files in the temporary/tmp directory are not used for a long time (10 days), the system executes the TMP directory cleaning service (systemd-tmpfiles-clean. Service), resulting in the cleaning of/TMP/undertow… 8090 files. However, when uploading, the undertow server needs to create/TMP/undertow… 8090/undertow… Upload temporary files, However, when calling files. CreateFile (…), you will find that the parent directory cannot be found, which leads to the above error.

3. Solution

1) Restart
cannot be done once and for all
2) the directory specified by the configuration file
needs to be manually created on the server
MKDIR – P/data/tmp

spring:
  servlet:
      multipart:
          location: /data/tmp

3) Add startup parameter – Java.TMP.Dir =/path/to/application/temp/