原文地址：https://www.iteye.com/blog/gearever-1540028

源碼面前，了無秘密?
???????????????????????????? ----侯捷?
在tomcat架構(gòu)分析(valve機(jī)制)(http://gearever.iteye.com/blog/1536022)里已經(jīng)對valve的機(jī)制做了分析?，F(xiàn)在通過源碼來加深下理解。侯捷說過，源碼面前，了無秘密。通過這些代碼，可以看到在tomcat中我們經(jīng)常碰到的一些現(xiàn)象或配置是怎么實(shí)現(xiàn)的。?
StandardEngineValve?
看一下StandardEngineValve的調(diào)用邏輯；?

Java代碼??

public?final?void?invoke(Request?request,?Response?response)??

????throws?IOException,?ServletException?{??

??

????//?定位host??

????Host?host?=?request.getHost();??

????if?(host?==?null)?{??

????????......??

????????return;??

????}??

??

????//?調(diào)用host的第一個valve??

????host.getPipeline().getFirst().invoke(request,?response);??

??

}??

可以清晰的看到，根據(jù)request定位到可以處理的host對象，同時，開始從頭調(diào)用host里的pipeline上的valve。?
StandardHostValve?
看一下StandardHostValve的調(diào)用邏輯；?

Java代碼??

public?final?void?invoke(Request?request,?Response?response)??

????throws?IOException,?ServletException?{??

??

????//?定位context??

????Context?context?=?request.getContext();??

????if?(context?==?null)?{??

????????......??

????????return;??

????}??

??

????......??

??

????//?調(diào)用context的第一個valve??

????context.getPipeline().getFirst().invoke(request,?response);??

??

????//?更新session??

????if?(Globals.STRICT_SERVLET_COMPLIANCE)?{??

????????request.getSession(false);??

????}??

??

????//?Error?page?processing??

????response.setSuspended(false);??

??

????//如果有拋異?；蚰硞€HTTP錯誤，導(dǎo)向響應(yīng)的配置頁面??

????Throwable?t?=?(Throwable)?request.getAttribute(Globals.EXCEPTION_ATTR);??

??

????if?(t?!=?null)?{??

????????throwable(request,?response,?t);??

????}?else?{??

????????status(request,?response);??

????}??

??

????//?Restore?the?context?classloader??

????Thread.currentThread().setContextClassLoader??

????????(StandardHostValve.class.getClassLoader());??

??

}??

可以清晰的看到，注釋部分里根據(jù)request定位到可以處理的context對象，同時，開始從頭調(diào)用context里的pipeline上的valve。在調(diào)用完context的所有的valve之后（當(dāng)然也是context調(diào)用完其對應(yīng)的wrapper上的所有valve之后），藍(lán)色部分顯示了拿到response對象時可以做的處理。?
熟悉tomcat的可能有配置錯誤信息的經(jīng)驗(yàn)，例如；?

Xml代碼??

<error-page>??

??<error-code>404</error-code>??

??<location>/error.jsp</location>??

?</error-page>??

它就是為了在用戶訪問資源出現(xiàn)HTTP 404錯誤時，將訪問重定向到一個統(tǒng)一的錯誤頁面。這樣做一是為了美觀，另一個主要作用是不會將一些具體的錯誤信息例如java拋異常時的棧信息暴露給用戶，主要還是出于安全的考慮。 上述代碼中的注釋部分就是實(shí)現(xiàn)這個重定向功能。?

StandardContextValve?
看一下StandardContextValve的調(diào)用邏輯；其代碼比較多，只貼一些比較核心的吧。?

Java代碼??

public?final?void?invoke(Request?request,?Response?response)??

????throws?IOException,?ServletException?{??

??

????......??

??

????//?定位wrapper??

????Wrapper?wrapper?=?request.getWrapper();??

????if?(wrapper?==?null)?{??

????????notFound(response);??

????????return;??

????}?else?if?(wrapper.isUnavailable())?{??

????????......??

????}??

??

????//?Normal?request?processing??

????//web.xml中配置web-app/listener/listener-class??

????Object?instances[]?=?context.getApplicationEventListeners();??

??

????ServletRequestEvent?event?=?null;??

??

????//響應(yīng)request初始化事件，具體的響應(yīng)listener是可配置的???

????......??

????//調(diào)用wrapper的第一個valve??

????wrapper.getPipeline().getFirst().invoke(request,?response);???

??

????//響應(yīng)request撤銷事件，具體的響應(yīng)listener是可配置的???

????......???????????????

}??

可以清晰的看到，注釋部分里根據(jù)request定位到可以處理的wrapper對象，同時，開始從頭調(diào)用wrapper里的pipeline上的valve。 需要注意的是，這里在調(diào)用wrapper的valve前后，分別有響應(yīng)request初始化及撤銷事件的邏輯，tomcat有一整套事件觸發(fā)體系，這里限于篇幅就不闡述了。有時間專門說。?
StandardWrapperValve?
看一下StandardWrapperValve的調(diào)用邏輯；其代碼比較多，只貼一些比較核心的吧；?

Java代碼??

public?final?void?invoke(Request?request,?Response?response)??

????throws?IOException,?ServletException?{??

??????

????......??

????requestCount++;??

????//定位wrapper??

????StandardWrapper?wrapper?=?(StandardWrapper)?getContainer();??

????Servlet?servlet?=?null;??

????Context?context?=?(Context)?wrapper.getParent();??

??????

????......??

??

????//?Allocate?a?servlet?instance?to?process?this?request??

????try?{??

????????if?(!unavailable)?{??

????????????//加載servlet??

????????????servlet?=?wrapper.allocate();??????????????????

????????}??

????}?catch?(UnavailableException?e)?{??

????????......??

????}???

????......??

????//?根據(jù)配置建立一個filter-servlet的處理鏈表，servlet在鏈表的尾端??

????ApplicationFilterFactory?factory?=??

????????ApplicationFilterFactory.getInstance();??

????ApplicationFilterChain?filterChain?=??

????????factory.createFilterChain(request,?wrapper,?servlet);??

????//?Reset?comet?flag?value?after?creating?the?filter?chain??

????request.setComet(false);??

??

????//?Call?the?filter?chain?for?this?request??

????//?NOTE:?This?also?calls?the?servlet's?service()?method??

????try?{??

????????String?jspFile?=?wrapper.getJspFile();??

????????if?(jspFile?!=?null)??

????????????request.setAttribute(Globals.JSP_FILE_ATTR,?jspFile);??

????????else??

????????????request.removeAttribute(Globals.JSP_FILE_ATTR);??

????????if?((servlet?!=?null)?&&?(filterChain?!=?null))?{??

????????????//?Swallow?output?if?needed??

????????????if?(context.getSwallowOutput())?{??

????????????????try?{??

????????????????????SystemLogHandler.startCapture();??

????????????????????if?(comet)?{??

????????????????????????filterChain.doFilterEvent(request.getEvent());??

????????????????????????request.setComet(true);??

????????????????????}?else?{??

????????????????????????//調(diào)用filter-servlet鏈表??

????????????????????????filterChain.doFilter(request.getRequest(),???

????????????????????????????????response.getResponse());??

????????????????????}??

????????????????}?finally?{??

????????????????????String?log?=?SystemLogHandler.stopCapture();??

????????????????????if?(log?!=?null?&&?log.length()?>?0)?{??

????????????????????????context.getLogger().info(log);??

????????????????????}??

????????????????}??

????????????}?else?{??

????????????????if?(comet)?{??

????????????????????request.setComet(true);??

????????????????????filterChain.doFilterEvent(request.getEvent());??

????????????????}?else?{??

????????????????????//調(diào)用filter-servlet鏈表??

????????????????????filterChain.doFilter??

????????????????????????(request.getRequest(),?response.getResponse());??

????????????????}??

????????????}??

??

????????}??

????????request.removeAttribute(Globals.JSP_FILE_ATTR);??

????}?catch?(ClientAbortException?e)?{??

????????request.removeAttribute(Globals.JSP_FILE_ATTR);??

????????throwable?=?e;??

????????exception(request,?response,?e);??

????}???

????......??

}??

可以清晰的看到，注釋部分里，先是能拿到相應(yīng)的wrapper對象；然后完成加載wrapper對象中的servlet，例如如果是jsp，將完成jsp編譯，然后加載servlet等；再然后，根據(jù)配置生成一個filter棧，通過執(zhí)行棧，調(diào)用完所有的filter之后，就調(diào)用servlet，如果沒有配置filter，就直接調(diào)用servlet，生成filter棧是通過request的URL模式匹配及servlet名稱來實(shí)現(xiàn)的，具體涉及的東西在tomcat的servlet規(guī)范實(shí)現(xiàn)中再闡述吧。?
以上，完成了一整套servlet調(diào)用的過程。通過上面的闡述，可以看見valve是個很靈活的機(jī)制，通過它可以實(shí)現(xiàn)很大的擴(kuò)展。?
Valve的應(yīng)用及定制化?
Tomcat除了提供上面提到的幾個標(biāo)準(zhǔn)的valve實(shí)現(xiàn)外，也提供了一些用于調(diào)試程序的valve的實(shí)現(xiàn)。實(shí)現(xiàn)valve需要繼承org.apache.catalina.valves.ValveBase基類。 以RequestDumperValve為例，?

引用 org.apache.catalina.valves.RequestDumperValve

RequestDumperValve是打印出request及response信息的valve。其實(shí)現(xiàn)方法為：?

Java代碼??

public?void?invoke(Request?request,?Response?response)???

????????????????throws?IOException,?ServletException?{???

??

????????Log?log?=?container.getLogger();???

??

????????//?Log?pre-service?information???

????????log.info("REQUEST?URI?="?+?request.getRequestURI());???

????????......???

????????log.info("?queryString="?+?request.getQueryString());???

????????......???

????????log.info("-------------------------------------------------------");???

??????????

????????//?調(diào)用下一個valve??

????????getNext().invoke(request,?response);???

??????????

????????//?Log?post-service?information???

????????log.info("-------------------------------------------------------");???

????????......???

????????log.info("?contentType="?+?response.getContentType());???

????????Cookie?rcookies[]?=?response.getCookies();???

????????for?(int?i?=?0;?i?<?rcookies.length;?i++)?{???

????????????log.info("?cookie="?+?rcookies[i].getName()?+?"="?+???

????????????????rcookies[i].getValue()?+?";?domain="?+???

????????????????rcookies[i].getDomain()?+?";?path="?+?rcookies[i].getPath());???

????????}???

????????String?rhnames[]?=?response.getHeaderNames();???

????????for?(int?i?=?0;?i?<?rhnames.length;?i++)?{???

????????????String?rhvalues[]?=?response.getHeaderValues(rhnames[i]);???

????????????for?(int?j?=?0;?j?<?rhvalues.length;?j++)???

????????????log.info("?header="?+?rhnames[i]?+?"="?+?rhvalues[j]);????????????

????????}??

????????log.info("?message="?+?response.getMessage());???

????????log.info("========================================================");???

??

}??

可以很清晰的看出，它打印出了request及response的信息，其中紅色部分顯示它調(diào)用valve鏈表中的下一個valve。我們可以這樣配置它；?

Xml代碼??

<Host?name="localhost"??appBase="webapps"??

????????????unpackWARs="true"?autoDeploy="true"??

????????????xmlValidation="false"?xmlNamespaceAware="false">??

??????<Valve?className="org.apache.catalina.valves.RequestDumperValve"/>??

??????<Context?path="/my"?docBase="?/usr/local/tomcat/backup/my"?>??????????????

??????</Context>??

??????<Context?path="/my2"?docBase="?/usr/local/tomcat/backup/my"?>?????????????

??????</Context>??

</Host>??

這樣，只要訪問此host下的所有context，都會打印出調(diào)試信息。 Valve的應(yīng)用有很多，例如cluster，SSO等，會有專門一章來講講。

轉(zhuǎn)載于:https://www.cnblogs.com/davidwang456/articles/11452742.html

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