無法在簡單彈簧mvc應用程序中注入bean

Question

我正在嘗試使用註釋的春天mvc中的一個簡單應用程序。在我的服務類中，即使使用了相關注釋，我也無法注入DAO類。請讓我知道我在做什麼錯誤。以下是我的班級定義。

  public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer { 

       @Override 
       protected Class<?>[] getRootConfigClasses() { 
        return new Class[] { SpringRootConfig.class }; 
        //return null; 
       } 

       @Override 
       protected Class<?>[] getServletConfigClasses() { 
        return new Class[] { SpringWebConfiguration.class }; 
       } 

       @Override 
       protected String[] getServletMappings() { 
        return new String[] { "/" }; 
       } 
      } 

     @Configuration 
     @EnableWebMvc 
     @ComponentScan(basePackages="com.emp.controller") 
     public class SpringWebConfiguration extends WebMvcConfigurerAdapter{ 

      @Bean 
      public InternalResourceViewResolver jspViewResolver() { 
      InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();  
         viewResolver.setPrefix("/WEB-INF/view/"); 
         viewResolver.setSuffix(".jsp"); 
         return viewResolver; 

       } 
      } 

    @Configuration 
    @EnableWebMvc 
    @ComponentScan(basePackages="com.emp.svc,com.emp.dao") 
    public class SpringRootConfig { 

    } 


    package com.emp.svc; 

    import org.springframework.beans.factory.annotation.Autowired; 
    import com.emp.dao.LoginDAO; 
    public class LoginSvc { 

     @Autowired 
     private LoginDAO dao; 

     public boolean validateLogin(){ 
      System.out.println("In the svc method"); 
      return dao.validateLogin(); 
     } 
    } 


    package com.emp.dao; 

    import org.springframework.stereotype.Component; 
    import org.springframework.stereotype.Repository; 

    @Repository 
    public class LoginDAO { 

     public boolean validateLogin(){ 
      System.out.println("In the DAO method"); 
      return true; 
     } 
    } 

package com.emp.controller; 

import org.springframework.stereotype.Controller; 
import org.springframework.web.bind.annotation.ModelAttribute; 
import org.springframework.web.bind.annotation.RequestMapping; 
import org.springframework.web.bind.annotation.RequestMethod; 
import org.springframework.web.servlet.ModelAndView; 

import com.emp.forms.LoginForm; 
import com.emp.svc.LoginSvc; 

@Controller 
public class LoginController { 

    @RequestMapping(value = {"/login"},method = RequestMethod.GET) 
    public ModelAndView launchLoginPage(){ 
     ModelAndView model = new ModelAndView(); 
     model.setViewName("login"); 
     return model; 
    } 

    @RequestMapping(value = {"/welcome"},method = RequestMethod.GET) 
    public ModelAndView validateLogin(@ModelAttribute LoginForm form){ 
     ModelAndView model = new ModelAndView(); 
     LoginSvc svc = new LoginSvc(); 
     if(svc.validateLogin()){ 
      model.setViewName("welcome"); 
     } 
     else 
     { 
      model.setViewName("login"); 
     } 
     return model; 
    } 

LoginSvc從控制器調用。我期待在LoginSvc中，LoginDAO將被注入，因此對dao.authateLogin（）的調用將會成功。但是我得到的是空指針在dao.validateLogin（），指示LoginDAO不被注入。

如果你能讓我知道我錯過了什麼，這將是很大的幫助。

Answer 1

在LoginSvc類中添加@Service註釋。

package com.emp.svc; 

import org.springframework.beans.factory.annotation.Autowired; 
import com.emp.dao.LoginDAO; 

@Service 
public class LoginSvc { 

    @Autowired 
    private LoginDAO dao; 

    public boolean validateLogin(){ 
     System.out.println("In the svc method"); 
     return dao.validateLogin(); 
    } 
} 

And your autowire LoginSvc inside your controller。由於您自己創建的對象調用LoginSvc的構造函數，因此spring不會爲您提供autowire候選。

@Controller 
public class LoginController { 

    @Autowired 
    private LoginSvc svc; 

    @RequestMapping(value = {"/login"},method = RequestMethod.GET) 
    public ModelAndView launchLoginPage(){ 
     ModelAndView model = new ModelAndView(); 
     model.setViewName("login"); 
     return model; 
    } 

    @RequestMapping(value = {"/welcome"},method = RequestMethod.GET) 
    public ModelAndView validateLogin(@ModelAttribute LoginForm form){ 
     ModelAndView model = new ModelAndView();    
     if(svc.validateLogin()) { 
      model.setViewName("welcome"); 
     } else { 
      model.setViewName("login"); 
     } 
     return model; 
    } 
}