@Autowired 验证器内部的 DAO答案

【问题标题】：@Autowired a DAO inside a Validator@Autowired 验证器内部的 DAO
【发布时间】：2014-03-16 08:51:26
【问题描述】：

是否可以在 Validator 中 @Autowired 一个 DAO ？当我使用它时，我得到一个空指针。当 userDAO 在验证器中被调用时，运行它会给我一个 NullPointerException。我包含所有代码和应用程序上下文

public class UserFormValidator implements Validator {

@Autowired
private UserDAO userDAO;  

@Override
public boolean supports(Class<?> clazz) {
    return UserForm.class.equals(clazz);
}

@Override
public void validate(Object target, Errors errors) {
    System.out.println ("User -> " + userDAO.findById(new Integer(1)));
}
}

@Repository("userDAO")
public class UserDAOImpl extends GenericDAOImpl implements UserDAO {

public UserDAOImpl() {
    super();
}
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:sws="http://www.springframework.org/schema/web-services"
xsi:schemaLocation="http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd
        http://www.springframework.org/schema/mvc 
        http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
        http://www.springframework.org/schema/web-services 
        http://www.springframework.org/schema/web-services/web-services-2.0.xsd">

<!-- Activates various annotations to be detected in bean classes -->
<context:annotation-config />

<!-- Scans the classpath for annotated components that will be auto-registered 
    as Spring beans. For example @Controller and @Service. Make sure to set the 
    correct base-package -->
<context:component-scan base-package="com.myapp" />
<context:annotation-config/>



<!-- Configures the annotation-driven Spring MVC Controller programming 
    model. Note that, with Spring 3.0, this tag works in Servlet MVC only! -->
<mvc:annotation-driven />

<!-- Load Hibernate related configuration -->
<!-- Here you can also add spring security context, if exist -->
<import resource="hibernate-context.xml" />


</beans>

谢谢！

【问题讨论】：

你的包名是什么？
你是如何实例化你的验证器的？
Why is my Spring @Autowired field null?的可能重复

标签： spring validation spring-mvc dependency-injection autowired

【解决方案1】：

尝试在 UserFormValidator 中添加@Component 注解

【讨论】：

【解决方案2】：

变化

binder.setValidator(new UserFormValidator());

为

binder.setValidator(userFormValidator);

解决了问题

【讨论】：

【解决方案3】：

验证器包名称：com.myapp.

添加@Component注解：

这里是我实例化验证器的控制器

@Controller
public class HomeController {

private static final Logger logger = LoggerFactory.getLogger(HomeController.class);


@InitBinder
protected void initBinder(WebDataBinder binder) {
    binder.setValidator(new UserFormValidator());
}

/**
 * Simply selects the home view to render by returning its name.
 */
@RequestMapping(value = "/home", method = RequestMethod.GET)
public String home(Locale locale, Model model) {

    model.addAttribute("userForm", new UserForm());
    return "home";
}

@RequestMapping(value = "/login",method = RequestMethod.POST)
 public String submitForm(@Valid UserForm  userForm, BindingResult result,ModelMap model) {

  if (result.hasErrors()) {
         return "home";
     }

  model.addAttribute("userForm",userForm);
  return "doors";

 }

@ModelAttribute("userForm")
public UserForm createModel() {
    return new UserForm();
}

}

【讨论】：