浅析SpringBoot中的过滤器和拦截器

public interface FilterChain {

    public void doFilter(ServletRequest request, ServletResponse response)
            throws IOException, ServletException;

}

public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        log.info("hello");
        chain.doFilter(request,response);
    }

    @Override
    public void destroy() {
        Filter.super.destroy();
    }
}

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
        /**
         * 1.
         * HandlerExecutionChain 是一个对象
         * 包含了以下重要的属性
         * private final Object handler; //处理器(controller和其最后的方法)
         * List<HandlerInterceptor> interceptorList = new ArrayList<>();//拦截器列表,用来存储匹配处理器的拦截器
         */
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

                /**
                 * 2.
                 * 下面这行代码 大概做了以下事情
                 * 1.通过request和url 匹配了对应的controller以及调用的方法 填充了HandlerExecutionChain.handler
                 * 2.通过匹配request和HandlerInterceptor的注册信息(拦截哪些,放行哪些),往HandlerExecutionChain.interceptorList中添加对应的拦截器
                 */
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = HttpMethod.GET.matches(method);
				if (isGet || HttpMethod.HEAD.matches(method)) {
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}
                /**
                 * 3.执行 拦截器链条中的所有前置方法
                 */
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

                /**
                 * 4.交由处理器(controller对应的方法)去处理方法中的业务逻辑
                 */
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}

				applyDefaultViewName(processedRequest, mv);
                
                /**
                 * 5.倒序执行 拦截器链条中的所有后置方法
                 */
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}}
        //...