【Spring深入解读】OncePerRequestFilter

最新推荐文章于 2023-11-14 15:25:49 发布

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最新推荐文章于 2023-11-14 15:25:49 发布

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分类专栏： Spring 文章标签： java spring

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本文详细介绍了Spring框架中OncePerRequestFilter的工作原理。该类通过对请求进行标记，确保每个HTTP请求仅被过滤一次，避免重复过滤的问题。具体实现上，通过设置一个标志属性来判断请求是否已被处理。

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我们发现Spring提供的URL请求Filter，都继承了OncePerRequestFilter类，

这个类是对原生的Filter进行优化，使Filter对请求不会循环调用，而是只调用一次，循环调用的将被忽略。

我们看一下源码：

/**
	 * This <code>doFilter</code> implementation stores a request attribute for
	 * "already filtered", proceeding without filtering again if the
	 * attribute is already there.
	 * @see #getAlreadyFilteredAttributeName
	 * @see #shouldNotFilter
	 * @see #doFilterInternal
	 */
	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;

		String alreadyFilteredAttributeName = getAlreadyFilteredAttributeName();
		if (request.getAttribute(alreadyFilteredAttributeName) != null || shouldNotFilter(httpRequest)) {
			// Proceed without invoking this filter...
			filterChain.doFilter(request, response);
		}
		else {
			// Do invoke this filter...
			request.setAttribute(alreadyFilteredAttributeName, Boolean.TRUE);
			try {
				doFilterInternal(httpRequest, httpResponse, filterChain);
			}
			finally {
				// Remove the "already filtered" request attribute for this request.
				request.removeAttribute(alreadyFilteredAttributeName);
			}
		}
	}

这个代码里面，OncePerRequestFilter实现了doFilter方法，并在过滤时，加入alreadyFilteredAttributeName这个属性，通过这个值，判断是不是循环调用了。