Question

我正在使用Spring DI并尝试在我的servlet中注入Spring服务。但是，它没有被注入并保持null，导致NullPointerException。

我的servlet：

@WebServlet(urlPatterns = {"/Register"}, displayName = "RegisterServlet")
public class RegisterServlet extends HttpServlet {

    @Autowired
    @Qualifier("registerServlet")
    public void setCustomerService(CustomerService customerService) {
        this.customerService = customerService;
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // ...
        customerService.save(customer); // Fail, because service is null.
        // ...
    }

}

我的spring-controller.xml：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="registerServlet" class="com.fishingstore.controller.RegisterServlet">
        <property name="customerService" ref="customerService"/>
    </bean>

</beans>

我的客户DAO课程：

@Repository
@Transactional
public class CustomerDAOImpl implements CustomerDAO {

    private SessionFactory sessionFactory;

    @Autowired
    @Qualifier("sessionFactory")
    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    // ...
}

我的客户服务类：

@Service
public class CustomerServiceImpl implements CustomerService {

    @Autowired
    @Qualifier("customerService")
    private CustomerDAO customerDAO;

    // ...
}

我的spring-service.xml：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="customerService" class="com.fishingstore.service.implementation.CustomerServiceImpl">
        <property name="customerDAO" ref="customerDAO"/>
    </bean>
</beans>

我的错误在哪里？

Answer 1

更改CustomerService限定符以匹配bean ID或更好地完全删除@Qualifier

@Autowired
@Qualifier("customerService")
public void setCustomerService(CustomerService customerService) {

对customerDAO

执行相同的操作

@Autowired
@Qualifier("customerDAO")
private CustomerDAO customerDAO;

Answer 2

Servlets不受Spring容器管理。显然，该类中的任何@Autowired注释都不会被处理。

Spring在类SpringBeanAutowiringSupport中提供了两种静态方法可以在servlet类中使用它来启用Autowiring功能。

processInjectionBasedOnCurrentContext(Object target)
processInjectionBasedOnServletContext(Object target, ServletContext servletContext)

使用第一种方法的示例是here，第二种方法的示例是here

这两种方法背后的想法是覆盖Servlet's init方法并启用bean的自动装配。

例如 -

@Override
    public void init(ServletConfig config) throws ServletException{
        super.init(config);
        SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);

    }

确保按照 @Reimeus 答案中的指示正确自动装配咖啡豆。

Spring服务没有注入web servlet

2 个答案: