Spring Boot中XML配置下@Autowired注入Repository为空问题求助

问题说明 #

在Spring Boot项目中，使用@Autowired注入继承CrudRepository的StudentRepo接口时，仅在通过spring.xml配置从控制器获取SignupService类实例的场景下，注入的studentRepo引用为空。由于XML配置要求Bean为类，无法直接为StudentRepo接口创建Bean，但已添加<jpa:repositories>标签扫描Repository包，问题仍存在。若不使用XML配置，仅在SignupService上添加@Component注解并在控制器中@Autowired注入SignupService，项目可正常运行，需解决@Autowired与XML配置的兼容问题。

报错信息 #

Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException: null 
at com.myspringproject1.service.SignupService.doSignup(SignupService.java:81) ~[classes/:na]
    at com.myspringproject1.controller.TestController.doSignup(TestController.java:42) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_202]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_202]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_202]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_202]

相关代码与配置 #

spring.xml配置 #

<beans ..... >
<context:annotation-config/>
    
    <bean id="signupServiceBean" class="com.myspringproject1.service.SignupService"></bean>
    <!-- <bean id="StudentRepoBean" class="com.myspringproject1.repo.StudentRepo"></bean> --> <!-- 注释掉的Repo接口Bean配置 -->
     
    <jpa:repositories base-package="com.myspringproject1.repo"/>
    
</beans>

Controller代码 #

@Controller
public class TestController {

@RequestMapping(method = RequestMethod.POST, value = "signup")
    public ModelAndView doSignup(HttpServletRequest request) {
        
        BeanFactory factory = new XmlBeanFactory(new ClassPathResource("spring.xml"));
        SignupService signupService = (SignupService) factory.getBean("signupServiceBean");
        
        
        ModelAndView mv = new ModelAndView();
        
        boolean result = signupService.doSignup(request);
        if (result == true) {
            User newUser = (User) request.getSession().getAttribute("user");
            mv.setViewName("signup_result");
            mv.addObject("newUser", newUser);
            return mv;
        }
    
        else {
            mv.setViewName("signup_result");
            mv.addObject("newUser", null);
            return mv;
        }
    }
}

Repository接口 #

@Repository
public interface StudentRepo extends CrudRepository<User, Integer>{

}

Service类 #

@Service
public class SignupService {

@Autowired
private StudentRepo studentRepo;

public boolean doSignup(HttpServletRequest request) {
    // 业务逻辑...
    User result = studentRepo.save(user); // 此处因studentRepo为空触发NullPointerException
    // 后续逻辑...
}
}

解决方案 #

1. 避免手动创建新的Spring容器 #

你在控制器中通过new XmlBeanFactory()创建了一个全新的Spring容器，这个容器和Spring Boot启动时初始化的主容器完全独立。主容器中会通过<jpa:repositories>生成StudentRepo的代理Bean，但新容器无法访问主容器的Bean，导致SignupService中的studentRepo无法被注入。

正确的做法是直接在控制器中@Autowired注入SignupService，无需手动从XML获取：

@Controller
public class TestController {

@Autowired
private SignupService signupService;

@RequestMapping(method = RequestMethod.POST, value = "signup")
    public ModelAndView doSignup(HttpServletRequest request) {
        ModelAndView mv = new ModelAndView();
        
        boolean result = signupService.doSignup(request);
        if (result) {
            User newUser = (User) request.getSession().getAttribute("user");
            mv.setViewName("signup_result");
            mv.addObject("newUser", newUser);
            return mv;
        }
    
        mv.setViewName("signup_result");
        mv.addObject("newUser", null);
        return mv;
    }
}

2. 将XML配置整合到Spring Boot主容器 #

如果必须保留XML配置，需要将spring.xml导入到Spring Boot的主容器中，而不是手动创建新容器。在Spring Boot启动类上添加@ImportResource注解：

@SpringBootApplication
@ImportResource("classpath:spring.xml")
public class YourApplication {
    public static void main(String[] args) {
        SpringApplication.run(YourApplication.class, args);
    }
}

这样XML中定义的signupServiceBean和<jpa:repositories>生成的Repository代理Bean都会被加载到主容器中，@Autowired可以正常注入依赖。

3. 确认Repository扫描配置生效 #

<jpa:repositories base-package="com.myspringproject1.repo"/>标签会自动扫描指定包下的Repository接口，并为其生成代理实现类作为Spring Bean，无需手动为接口配置Bean。确保base-package的值正确指向你的Repository所在包，主容器就能扫描到这些Bean并完成注入。

内容的提问来源于stack exchange，提问作者Zeeshan