1、問題描述

SpringBoot中filter注入bean時注入失敗，bean一直為空。

@Slf4j
@Component
public class RestAuthFilter extends FormAuthenticationFilter {

    //實際注入為null
    @Autowired
    MobileDeviceService mobileDeviceService;

    @Autowired
    UserService userService;

    ...
}

2、問題探究

其實Spring中，web應用啟動的順序是：listener->filter->servlet

，先初始化listener，然後再來就filter的初始化，再接著才到我們的dispathServlet的初始化，因此，當我們需要在filter裡注入一個註解的bean時，就會注入失敗，因為filter初始化時，註解的bean還沒初始化，沒法注入。

3、解決方法

/**
 * 解決Filter中注入Bean失敗
 * Created by hoaven on 2018/5/30.
 */
@Slf4j
@Component
public class SpringUtils implements ApplicationContextAware {

    private static ApplicationContext applicationContext;

    @Override
 

    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {
        if (SpringUtils.applicationContext == null) {
            SpringUtils.applicationContext = applicationContext;
        }

    }

    public static ApplicationContext getApplicationContext
 
() {
        return applicationContext;
    }

    //根據name
    public static Object getBean(String name) {
        return getApplicationContext().getBean(name);
    }

    //根據型別
    public static <T> T getBean(Class<T> clazz) {
        return getApplicationContext().getBean(clazz);
    }

    public static <T> T getBean(String name, Class<T> clazz) {
        return getApplicationContext().getBean(name, clazz);
    }

}

使用：

if (mobileDeviceService == null) {
    mobileDeviceService = (MobileDeviceService) SpringUtils.getBean("mobileDeviceServiceImpl");
}
if (userService == null) {
    userService = (UserService) SpringUtils.getBean("userServiceImpl");
}