SSM框架中Filter使用@Autowired注入Service

版本信息：
Spring:4.3.10

  最近遇到一个功能点，需要在 Controller 未接收到请求之前，添加请求携带的参数。在询问多位网友开发者，他们推荐使用 Filter，并且建议我读 Shiro 的源码（这源码之前读过，没看懂，哈哈~）。

第一次尝试：

public class LoginFilter implements Filter{
    @Autowired
    private Service Service;

        @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        int uid = Service.getUid(cert);
        request.setAttribute("uid", String.valueOf(uid));
        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {
    }
}

结论：失败告终，Service注入失败，为null。原因是因为 Filter 运行在 Spring注入bean之前，导致Filter 内注入的值为 null。

第二次尝试:

private Services service;
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        if(service==null){
            ServletContext servletContext = request.getServletContext();
            WebApplicationContext webApplicationContext = WebApplicationContextUtils.getWebApplicationContext(servletContext);
            service = webApplicationContext.getBean(Services.class);
        }
        int uid = Service.getUid(cert);
    request.setAttribute("uid", String.valueOf(uid));
    chain.doFilter(request, response);  
    }

结论：失败；

第三次尝试:

public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {

        SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(this);
        int uid = Service.getUid(cert);
        request.setAttribute("uid", String.valueOf(uid));
        chain.doFilter(request, response);
}

结论：失败；
.
.
.

后来我看到很多人推荐 利用 org.springframework.web.filter.DelegatingFilterProxy 来把 Filter 注入到Spring中，于是就有了 第n次、第n+1次尝试。
第n+1次尝试：
web.xml

    <filter>      
       <filter-name>loginFilter</filter-name>    
       <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>      
       <init-param>          
           <param-name>targetFilterLifecycle</param-name>          
           <param-value>true</param-value>      
       </init-param>  
   </filter>
   <filter-mapping>
       <filter-name>loginFilter</filter-name>
       <url-pattern>/*</url-pattern>
   </filter-mapping>

spring-servlet.xml

    <bean id="loginFilter" class="com.xxxxx.xxxxx.filter.LoginFilter"></bean>

结论：完美；

参考：

https://stackoverflow.com/questions/30554688/get-the-autowired-service-in-filter-class
https://stackoverflow.com/questions/32127258/how-to-autowire-bean-in-the-servlet-filters-in-spring-application
http://learningviacode.blogspot.com/2013/12/delegatingfilterproxy-and-spring.html
https://stackoverflow.com/questions/32494398/unable-to-autowire-the-service-inside-my-authentication-filter-in-spring