[spring] Filter - Githubissues

OncePerRequestFilter

OncePerRequestFilter 是在一次外部请求中只过滤一次, 对于服务器内部之间的forward等请求, 不会再次执行过滤方法
Spring Security里面被广泛用到

通过增加标记的方式来实现过滤器只被执行一次

public abstract class OncePerRequestFilter extends GenericFilterBean {
        //一个标记，后面会用到
    public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";

    @Override
    public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {

        if (!(request instanceof HttpServletRequest) || !(response instanceof HttpServletResponse)) {
            throw new ServletException("OncePerRequestFilter just supports HTTP requests");
        }
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        //这里获取一个名称，该名称后面会被用于放到request当作key
        String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
        //检测当前请求是否已经拥有了该标记，如果拥有该标记则代表该过滤器执行过了（后面注释有说明）
        boolean hasAlreadyFilteredAttribute = request.getAttribute(alreadyFilteredAttributeName) != null;

        if (skipDispatch(httpRequest) || shouldNotFilter(httpRequest)) {

            // Proceed without invoking this filter...
            filterChain.doFilter(request, response);
        }
        //如果此过滤器已经被执行过则执行如下的逻辑
        else if (hasAlreadyFilteredAttribute) {

            if (DispatcherType.ERROR.equals(request.getDispatcherType())) {
                doFilterNestedErrorDispatch(httpRequest, httpResponse, filterChain);
                return;
            }

            // Proceed without invoking this filter...
            filterChain.doFilter(request, response);
        }
        //走到这里说明该过滤器没有被执行过
        else {
            // Do invoke this filter...
            // 在当前请求里面设置一个标记，key就是前面拼接的那个变量，value是true，这个标记如果在request存在则在前面会被检测到并改变hasAlreadyFilteredAttribute的值
            request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);
            try {
                                // 这个方法是一个抽象方法需要子类去实现具体的过滤逻辑
                doFilterInternal(httpRequest, httpResponse, filterChain);
            }
            finally {
                // Remove the "already filtered" request attribute for this request.
                // 执行完毕之后移除该标记
                request.removeAttribute(alreadyFilteredAttributeName);
            }
        }
    }
    //其余代码略
}

Alice52 / spring-5.2.x

[spring] Filter #31

OncePerRequestFilter