过滤器中使用spring容器注入bean

转自：https://blog.youkuaiyun.com/jslcylcy/article/details/59114866

tomcat容器初始化顺序监听器–>过滤器–>servlet，因此springMVCservlet初始化之前，过滤器就已经初始化过了，如果在过滤器中需要注入spring容器管理的bean是注入不进去的，因此需要在spring监听器中初始化需要注入的bean，才能在过滤器中注入，而且过滤器的定义需要使用spring定义的DelegatingFilterProxy来实现，web.xml部分代码如下

    <filter>
        <filter-name>testFilter</filter-name>
        <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>testFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

其余部分只需要在spring容器中加载testFilter就行了，例子testFilter如下： 
注意此处的filter必须为实现javax.Filter的类，而且初始化需要放在spring监听器中，即必须在过滤器初始化之前初始化

@Component
public class TestFilter implements Filter
{
    private static final Logger logger = LogManager.getLogger(TestFilter.class);

    @Autowired
    private UserService userService;

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
        throws ServletException, IOException
    {
        logger.info(JSONArray.fromObject(userService.list()));
        filterChain.doFilter(request, response);
    }

    @Override
    public void init(FilterConfig filterConfig)
        throws ServletException
    {
        logger.info("初始化filter");
    }

    @Override
    public void destroy()
    {
        logger.info("destroyfilter");
    }
}

如果要保留Filter原有的init，destroy方法的调用，还需要配置初始化参数targetFilterLifecycle为true，该参数默认为false，代码例子如下：

    <filter>
        <filter-name>testFilter</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>testFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>