Cannot get value with @value, null

In the use of @Value When , It can be downloaded from properties Get the value from the file , Such operation can enhance the decoupling of the program , When using this annotation today, even if the assignment , But I can only get it null
Major errors ：
1. Not used on class @Component Annotations or other derived annotations , Make it a container ,spring You can't get it properties Value .
2. When calling this class , Not used @Autowired Make it inject automatically , It USES new The way , In this way, there is no value .

Here's the right way ：

• Util class

...
@Component    // Must be added 
public class BmsUtil {
    
	@Value("${file.uploadFolder}")
	private String realBasePath;
	...
}

• Service class

...
@Service // Must be added ,@Service yes @Component Derived notes for 
public class BookServiceImpl implements BookService {
    
	@Autowired
	BookMapper bookMapper;
	@Autowired  // When calling a class , Need to use @Autowired Automatic injection 
	BmsUtil bmsUtil;
	...
}

• properties

spring.thymeleaf.cache=false
# Set up sql The statement is output on the console 
logging.level.com.muyu.bms.mapper=debug
#windows Upload image path 
file.uploadFolder=E:/code/IDEA code/BMS/src/main/resources/static/upload
#linux Upload image path 
#file.uploadFolder=/usr/local/tomcat/apache-tomcat/webapps/ROOT/WEB-INF/classes/static/upload

There is another case @Value You can't get the value , Is called in the constructor @Value Action variables , And assign a value to it .

================================
Look back at this problem after a long time , In fact, it has been well understood ,@Value yes Spring,IOC A way to inject parameters , So we have to add @Component Etc. derived annotation , Give it to Spring management ,@Autowired It's the same thing , Use this annotation Spring Will inject the value .
Call the constructor to create an object ,@Value The reason why the value cannot be obtained is , You didn't use Spring Method to get the object , I created an object myself , Naturally, you can't get it Spring The injected value .