Can not set field to com.sun.proxy.$Proxy

Can not set 'FileValidator' field 'FileController.validator' to 'com.sun.proxy.$Proxy101'

FileValidator is a class, not an interface.

com.sun.proxy.$Proxy101 is an interface proxy, not a class proxy.

There are two main ways to solve this. Either inject the validator via an interface, e.g:

@Autowired @Qualifier("fileValidator")
private Validator fileValidator;

or enable class-proxies, e.g:

@SpringBootApplication
@EnableAspectJAutoProxy(proxyTargetClass = true)
public class Application {

Those are just examples, there will be other ways to implement those two solutions.

Autowire the interface of FileValidator(class) in your class FileController. Doing this will not require you to specify @Qualifier as mentioned below:

@Autowired
IFileValidator filevalidator;