OSCache源码阅读(一)

浏览数：33 / 时间：2015年06月20日

自己在开发JavaEE的项目时，采用了基于Spring MVC + MyBatis +Sitemesh +AngularJS + semantic-ui的组合，使用maven作为项目管理、SVN作为代码版本控制工具。

前台通过ajax从后台获取数据，再在前台进行DOM渲染，于是，数据加载的时候，页面会有一定程度的"空白"现象。

为了解决这个问题，最好的办法的是把动态页面静态化，页面只进行一次渲染，但这种方式，略显麻烦，于是自己采取了片段化缓存和数据缓存的方式，加快

页面渲染和数据加载。

1.配置

页面片段化缓存

为了统一页面风格，我使用Sitemesh来做页面布局。于是，页首的导航栏、菜单栏、页面底部的版权信息，可以直接缓存掉，比如下图(-1表示永久缓存)。

技术分享

打开页面的速度确实提升很快。

数据缓存

对于页面、数据接口进行全局缓存，在web.xml配置如下:

<!-- osCacheFilter -->
	<filter>
		<filter-name>osCacheFilter</filter-name>
		<filter-class>com.opensymphony.oscache.web.filter.CacheFilter</filter-class>
		<init-param>
			<param-name>time</param-name>
			<param-value>7200</param-value><!-- 2h -->
		</init-param>
		<init-param>
			<param-name>scope</param-name>
			<param-value>application</param-value><!-- default -->
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/</url-pattern><!-- home page -->
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/group/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/article/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/case/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/disease/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/doctor/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/drug/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/hospital/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/page/*</url-pattern>
	</filter-mapping>
	<filter-mapping>
		<filter-name>osCacheFilter</filter-name>
		<url-pattern>/u/*</url-pattern>
	</filter-mapping>

2.源码

个人从github上得到相关源码，地址：https://github.com/cdemoustier/opensymphony-oscache-backup

web.xml这么配置参数，是如何被OSCache得到呢？

先看com.opensymphony.oscache.web.filter.CacheFilter类，它的init方法如下：

/**
	 * Initialize the filter. This retrieves a {@link ServletCacheAdministrator}
	 * instance and configures the filter based on any initialization
	 * parameters.
	 * <p>
	 * The supported initialization parameters are:
	 * <ul>
	 * 
	 * <li><b>oscache-properties-file</b> - the properties file that contains
	 * the OSCache configuration options to be used by the Cache that this
	 * Filter should use.</li>
	 * 
	 * @param filterConfig
	 *            The filter configuration
	 */
	public void init(FilterConfig filterConfig) {
		// Get whatever settings we want...
		config = filterConfig;

		log.info("OSCache: Initializing CacheFilter with filter name "
				+ config.getFilterName());

		// setting the request filter to avoid reentrance with the same filter
		requestFiltered = REQUEST_FILTERED + config.getFilterName();
		log.info("Request filter attribute is " + requestFiltered);

		// filter Properties file
		Properties props = null;
		try {
			String propertiesfile = config
					.getInitParameter("oscache-properties-file");

			if (propertiesfile != null && propertiesfile.length() > 0) {
				props = Config.loadProperties(
						propertiesfile,
						"CacheFilter with filter name '"
								+ config.getFilterName() + "'");
			}
		} catch (Exception e) {
			log.info("OSCache: Init parameter 'oscache-properties-file' not set, using default.");
		}
		admin = ServletCacheAdministrator.getInstance(
				config.getServletContext(), props);

		// filter parameter time
		String timeParam = config.getInitParameter("time");
		if (timeParam != null) {
			try {
				setTime(Integer.parseInt(timeParam));
			} catch (NumberFormatException nfe) {
				log.error("OSCache: Unexpected value for the init parameter 'time', defaulting to one hour. Message="
						+ nfe.getMessage());
			}
		}

		// filter parameter scope
		String scopeParam = config.getInitParameter("scope");
		if (scopeParam != null) {
			if ("session".equalsIgnoreCase(scopeParam)) {
				setCacheScope(PageContext.SESSION_SCOPE);
			} else if ("application".equalsIgnoreCase(scopeParam)) {
				setCacheScope(PageContext.APPLICATION_SCOPE);
			} else {
				log.error("OSCache: Wrong value '"
						+ scopeParam
						+ "' for init parameter 'scope', defaulting to 'application'.");
			}

		}

		// filter parameter cron
		setCron(config.getInitParameter("cron"));
		....

		// filter parameter scope
		String disableCacheOnMethodsParam = config
				.getInitParameter("disableCacheOnMethods");
		if (StringUtil.hasLength(disableCacheOnMethodsParam)) {
			disableCacheOnMethods = StringUtil.split(
					disableCacheOnMethodsParam, ',');
			// log.error("OSCache: Wrong value '" + disableCacheOnMethodsParam +
			// "' for init parameter 'disableCacheOnMethods', defaulting to 'null'.");
		}

	}

通过FilterConfig filterConfig来获取参数值，完成初始化。

那Cache是如何对request进行过滤呢？

public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws ServletException, IOException {
		if (log.isInfoEnabled()) {
			log.info("OSCache: filter in scope " + cacheScope);
		}

		// avoid reentrance (CACHE-128) and check if request is cacheable
		if (isFilteredBefore(request) || !isCacheableInternal(request)) {
			chain.doFilter(request, response);
			return;
		}
		//标记:已过滤
		request.setAttribute(requestFiltered, Boolean.TRUE);

		HttpServletRequest httpRequest = (HttpServletRequest) request;

		// checks if the response will be a fragment of a page
		boolean fragmentRequest = isFragment(httpRequest);

		// avoid useless session creation for application scope pages
		// (CACHE-129)
		Cache cache;
		if (cacheScope == PageContext.SESSION_SCOPE) {
			cache = admin.getSessionScopeCache(httpRequest.getSession(true));
		} else {
			cache = admin.getAppScopeCache(config.getServletContext());
		}

		// generate the cache entry key
		String key = cacheKeyProvider.createCacheKey(httpRequest, admin, cache);

		try {
			ResponseContent respContent = (ResponseContent) cache.getFromCache(
					key, time, cron);

			if (log.isInfoEnabled()) {
				log.info("OSCache: Using cached entry for " + key);
			}

			boolean acceptsGZip = false;
			if ((!fragmentRequest) && (lastModified != LAST_MODIFIED_OFF)) {
				long clientLastModified = httpRequest
						.getDateHeader(HEADER_IF_MODIFIED_SINCE); // will return
																	// -1 if no
																	// header...

				// only reply with SC_NOT_MODIFIED
				// if the client has already the newest page and the response
				// isn't a fragment in a page
				if ((clientLastModified != -1)
						&& (clientLastModified >= respContent.getLastModified())) {
					((HttpServletResponse) response)
							.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
					return;
				}

				acceptsGZip = respContent.isContentGZiped()
						&& acceptsGZipEncoding(httpRequest);
			}

			respContent.writeTo(response, fragmentRequest, acceptsGZip);
			// acceptsGZip is used for performance reasons above; use the
			// following line for CACHE-49
			// respContent.writeTo(response, fragmentRequest,
			// acceptsGZipEncoding(httpRequest));
		} catch (NeedsRefreshException nre) {
			boolean updateSucceeded = false;

			try {
				if (log.isInfoEnabled()) {
					log.info("OSCache: New cache entry, cache stale or cache scope flushed for "
							+ key);
				}

				CacheHttpServletResponseWrapper cacheResponse = new CacheHttpServletResponseWrapper(
						(HttpServletResponse) response, fragmentRequest,
						time * 1000L, lastModified, expires,
						cacheControlMaxAge, etag);
				chain.doFilter(request, cacheResponse);
				cacheResponse.flushBuffer();

				// Only cache if the response is cacheable
				if (isCacheableInternal(cacheResponse)) {
					// get the cache groups of the content
					String[] groups = cacheGroupsProvider.createCacheGroups(
							httpRequest, admin, cache);
					// Store as the cache content the result of the response
					cache.putInCache(key, cacheResponse.getContent(), groups,
							expiresRefreshPolicy, null);
					updateSucceeded = true;
					if (log.isInfoEnabled()) {
						log.info("OSCache: New entry added to the cache with key "
								+ key);
					}
				}
			} finally {
				if (!updateSucceeded) {
					cache.cancelUpdate(key);
				}
			}
		}
	}

对request过滤后，添加标志位，避免重复缓存。

郑重声明：本站内容如果来自互联网及其他传播媒体，其版权均属原媒体及文章作者所有。转载目的在于传递更多信息及用于网络分享，并不代表本站赞同其观点和对其真实性负责，也不构成任何其他建议。

OSCache源码阅读(一)