1. Null pointer exception:

Request processing failed; nested exception is java.lang.NullPointerException

java.lang.NullPointerException
com.atguigu.mvc.controller.NodesController.getFilesAndSendId(NodesController.java:61)

See the exception address and check the control layer

Control level, line 61:

List<FilePath> files = fileService.getFiles();

current

@RequestMapping(value = "/getFilesAndSendId/{sensor_id}",method = RequestMethod.GET)

Parameter sensor_id is passed；

Solution to null pointer:
Original:

private FileService fileService;

Change to: add @Autowired annotation

 @Autowired
    private FileService fileService;

If there is any other error when you run the codes:

Servlet.init() of Servlet[DispatcherServlet] raises an exception.
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name ‘nodesController’: Unsatisfied dependency expressed through field ‘fileService’; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type ‘com.atguigu.mvc.service.FileService’ available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}

Solution:
Check if the @Service annotation is added to the implementation class here