我一直在尝试使用一个可以与mysql和jasperreports集成的springboot项目。其想法是用户可以将任何人添加到数据库中，然后打印一个包含所有实体的报告。错误出现在我的控制器上的viewReport（）函数中。它显示this.userService为空

@Controller
public class AppController {

@Autowired
private UserRepository repo;
private UserService userService;

@GetMapping("")
public String viewHomePage() {
    return "index";
}

@GetMapping("/register")
public String showSignUpForm(Model model) {
    model.addAttribute("user", new User());
    
    return "signup_form";
}

@GetMapping("/report")
public String generateReport() {
    userService.viewReport();
    
    return "index";
}

@PostMapping("/process_register")
public String processRegistration(User user) {
    repo.save(user);
    
    return "register_success";
}
}

这是我的控制器。错误是userService.viewReport（）;

@Service
public class UserService {
    
    @Autowired
    private UserRepository repo;
    
    public String viewReport() {
        Log.info("Preparing the pdf report via Jasper.");
        try {
            createPdfReport(repo.findAll());
            Log.info("File successfully saved at given path.");
        } catch (final Exception e) {
            Log.error("Some error has occured while preparing PDF document.");
            e.printStackTrace();
        }
        return "Done in ViewReport";
    }
    
    public void createPdfReport(final List<User> users) throws JRException {
        //Fetching .jrxml file from resources folder.
        final InputStream stream = this.getClass().getResourceAsStream("/report.jrxml");
        
        //compile report from .jrxml to .jasper
        final JasperReport report = JasperCompileManager.compileReport(stream);
        
        //Fetch users from the data source
        final JRBeanCollectionDataSource source = new JRBeanCollectionDataSource(users);
        
        //Adding the additional parameters to the pdf
        final Map<String, Object> parameters = new HashMap<>();
        parameters.put("CreatedBy", "edu.sru.Smith" );
        
        //filling report with data from database
        final JasperPrint print = JasperFillManager.fillReport(report, parameters, source);
        
        //place file in c:drive
        final String filePath = "C://CPSC-488";
        //export report to pdf file
        JasperExportManager.exportReportToPdfFile(print, filePath + "Employee_Report.pdf");
        
    }
    
} ```

That is my service class that autofills with the data from the MySQL database. I have tried adding a number of annotations and other things, but I haven't had success with anything. I'm honestly just new to this whole springboot thing and annotations overall and I have no idea where to go from here.