传统spring踩坑

filter 中的自动注入

最近把一个用于springboot中的组件，要放入传统的spring-mvc中去，以为没什么问题。直到拉了一个前置机工程(spring-mvc)，中间的一个过滤器都是空指针。

大概代码如下

@Component
@WebFilter(urlPatterns = "/*", filterName = "rateAndMetricsFilter")
public class RateAndMetricsFilter implements Filter, Runnable {

    private Logger logger = LoggerFactory.getLogger(getClass());

    @Value("${enable.db.store:false}")
    private boolean enableDBStore = false;

    @Autowired
    private RateLimiter rateLimiter;
  
@Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        // 限流了抛出运行时异常
        rateLimiter.limit(uri);
        chain.doFilter(servletRequest, servletResponse);
    }
}

中间的这个rateLimiter，自动注入未成功一直导致空指针。

传统spring-mvc的启动流程 context-param -> listener -> filter -> servlet，servlet在filter之后也就意味着org.springframework.web.servlet.DispatcherServlet都没有实例化，如此一来自动注入肯定会失败

解决方案

有2种，一种显示初始化spring容器，第二种将过滤器在xml中交给spring的delegate

    public void init(FilterConfig filterConfig) throws ServletException {
        //在filter 获取spring上下文
        ServletContext context = filterConfig.getServletContext();
        ApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(context);
        if(enableDBStore){
            jdbcTemplate = ctx.getBean(JdbcTemplate.class);
        }
        rateLimiter = ctx.getBean(RateLimiter.class);
        Environment environment = ctx.getEnvironment();
        if(environment.containsProperty("enable.db.store")){
            enableDBStore = environment.getProperty("enable.db.store",Boolean.class);
        }
    }

<!-- web.xml中添加DelegatingFilterProxy， -->
<filter>
		<filter-name>frontMonitorFilter</filter-name>
		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
		<init-param>
			<param-name>targetBeanName</param-name>
			<param-value>rateAndMetricsFilter</param-value>
		</init-param>
	</filter>
<!-- 声明这个bean -->
	<bean id="rateAndMetricsFilter" class="com.gzhc365.limit.filter.RateAndMetricsFilter"></bean>

仔细查看了一下DelegatingFilterProxy的源代码,他也是获取springContext，在到springContext中获取这个filter

    protected void initFilterBean() throws ServletException {
        synchronized(this.delegateMonitor) {
            if (this.delegate == null) {
                if (this.targetBeanName == null) {
                    this.targetBeanName = this.getFilterName();
                }

                WebApplicationContext wac = this.findWebApplicationContext();
                if (wac != null) {
                    this.delegate = this.initDelegate(wac);
                }
            }

        }
    }
    protected Filter initDelegate(WebApplicationContext wac) throws ServletException {
        Filter delegate = (Filter)wac.getBean(this.getTargetBeanName(), Filter.class);
        if (this.isTargetFilterLifecycle()) {
            delegate.init(this.getFilterConfig());
        }

        return delegate;
    }

haogui

传统spring-mvc中的filter进行自动注入

传统spring踩坑

filter 中的自动注入

解决方案

限流器