本文主要目的是講解tomcat中的pipeline機(jī)制，涉及部分源碼分析

之前我們?cè)谇懊娴奈恼陆榻B過(guò)，tomcat中Container有4種，分別是Engine,Host,Context,Wrapper，這4個(gè)Container的實(shí)現(xiàn)類分別是StandardEngine,StandardHost,StandardContext,StandardWrapper。4種容器的關(guān)系是包含關(guān)系，Engine包含Host,Host包含Context,Context包含Wrapper,Wrapper則代表最基礎(chǔ)的一個(gè)Servlet。

之前在tomcat架構(gòu)簡(jiǎn)述那篇文章中介紹過(guò)，tomcat由Connector和Container兩部分組成，而當(dāng)網(wǎng)絡(luò)請(qǐng)求過(guò)來(lái)的時(shí)候Connector先將請(qǐng)求包裝為Request，然后將Request交由Container進(jìn)行處理，最終返回給請(qǐng)求方。而Container處理的第一層就是Engine容器，但是在tomcat中Engine容器不會(huì)直接調(diào)用Host容器去處理請(qǐng)求，那么請(qǐng)求是怎么在4個(gè)容器中流轉(zhuǎn)的，4個(gè)容器之間是怎么依次調(diào)用的，我們今天來(lái)講解下。

當(dāng)請(qǐng)求到達(dá)Engine容器的時(shí)候，Engine并非是直接調(diào)用對(duì)應(yīng)的Host去處理相關(guān)的請(qǐng)求，而是調(diào)用了自己的一個(gè)組件去處理，這個(gè)組件就叫做pipeline組件,跟pipeline相關(guān)的還有個(gè)也是容器內(nèi)部的組件，叫做valve組件。

Pipeline的作用就如其中文意思一樣管道，可以把不同容器想象成一個(gè)獨(dú)立的個(gè)體，那么pipeline就可以理解為不同容器之間的管道，道路，橋梁。那Valve這個(gè)組件是什么東西呢？Valve也可以直接按照字面意思去理解為閥門(mén)。pipeline是通道，valve是閥門(mén)，他們兩有什么關(guān)系呢？

就像上圖那樣，每個(gè)管道上面都有閥門(mén)，Pipeline和Valve關(guān)系也是一樣的。Valve代表管道上的閥門(mén)，可以控制管道的流向，當(dāng)然每個(gè)管道上可以有多個(gè)閥門(mén)。如果把Pipeline比作公路的話，那么Valve可以理解為公路上的收費(fèi)站，車代表Pipeline中的內(nèi)容，那么每個(gè)收費(fèi)站都會(huì)對(duì)其中的內(nèi)容做一些處理(收費(fèi)，查證件等)。

好了舉例說(shuō)完了，我們繼續(xù)回歸tomcat。在Catalina中，我們有4種容器，每個(gè)容器都有自己的Pipeline組件，每個(gè)Pipeline組件上至少會(huì)設(shè)定一個(gè)Valve(閥門(mén))，這個(gè)Valve我們稱之為BaseValve（基礎(chǔ)閥）。基礎(chǔ)閥的作用是連接當(dāng)前容器的下一個(gè)容器(通常是自己的自容器),可以說(shuō)基礎(chǔ)閥是兩個(gè)容器之間的橋梁。

Pipeline定義對(duì)應(yīng)的接口Pipeline,標(biāo)準(zhǔn)實(shí)現(xiàn)了StandardPipeline。Valve定義對(duì)應(yīng)的接口Valve,抽象實(shí)現(xiàn)類ValveBase,4個(gè)容器對(duì)應(yīng)基礎(chǔ)閥門(mén)分別是StandardEngineValve,StandardHostValve,StandardContextValve,StandardWrapperValve。在實(shí)際運(yùn)行中Pipeline,Valve運(yùn)行機(jī)制如下圖。

在單個(gè)容器中Pipeline，Valve運(yùn)行圖

Catalina中Pipeline,Valve運(yùn)行圖

可以看到在同一個(gè)Pipeline上可以有多個(gè)Valve,每個(gè)Valve都可以做一些操作，無(wú)論是Pipeline還是Valve操作的都是Request和Response。而在容器之間Pipeline和Valve則起到了橋梁的作用,那么具體內(nèi)部原理是什么，我們開(kāi)始查看源碼。

Valve

public interface Valve {public String getInfo();public Valve getNext();public void setNext(Valve valve);public void backgroundProcess();public void invoke(Request request, Response response) throws IOException, ServletException;public void event(Request request, Response response, CometEvent event) throws IOException,ServletException;public boolean isAsyncSupported();}

先看Valve接口的方法定義，方法不是很多，這里只介紹setNext(),getNext()。在上面我們也看到了一個(gè)Pipeline上面可以有很多Valve，這些Valve存放的方式并非統(tǒng)一存放在Pipeline中，而是像一個(gè)鏈表一個(gè)接著一個(gè)。當(dāng)你獲取到一個(gè)Valve實(shí)例的時(shí)候，調(diào)用getNext()方法即可獲取在這個(gè)Pipeline上的下個(gè)Valve實(shí)例。

Pipeline

//pipeline 接口 public interface Pipeline {public Valve getBasic();public void setBasic(Valve valve);public void addValve(Valve valve);public Valve[] getValves();public void removeValve(Valve valve);public Valve getFirst();public boolean isAsyncSupported();public Container getContainer();public void setContainer(Container container);}

可以看出Pipeline中很多的方法都是操作Valve的，包括獲取，設(shè)置，移除Valve,getFirst()返回的是Pipeline上的第一個(gè)Valve,而getBasic(),setBasic()則是獲取/設(shè)置基礎(chǔ)閥,我們都知道在Pipeline中，每個(gè)pipeline至少都有一個(gè)閥門(mén)，叫做基礎(chǔ)閥，而getBasic(),setBasic()則是操作基礎(chǔ)閥的。

StandardPipeline

public class StandardPipeline extends LifecycleBase implements Pipeline, Contained {private static final Log log = LogFactory.getLog(StandardPipeline.class);// ----------------------------------------------------------- Constructorspublic StandardPipeline() {this(null); }public StandardPipeline(Container container) {super();setContainer(container); }// ----------------------------------------------------- Instance Variablesprotected Valve basic = null;protected Container container = null;protected static final String info = "org.apache.catalina.core.StandardPipeline/1.0";protected Valve first = null;//1111111111 @Override protected synchronized void startInternal() throws LifecycleException {// Start the Valves in our pipeline (including the basic), if anyValve current = first;if (current == null) {current = basic;}while (current != null) {if (current instanceof Lifecycle)((Lifecycle) current).start();current = current.getNext();}setState(LifecycleState.STARTING); }// ------------------------------------------------------- Pipeline Methods //2222222222222222222222 @Override public void setBasic(Valve valve) {// Change components if necessaryValve oldBasic = this.basic;if (oldBasic == valve)return;// Stop the old component if necessaryif (oldBasic != null) {if (getState().isAvailable() && (oldBasic instanceof Lifecycle)) {try {((Lifecycle) oldBasic).stop();} catch (LifecycleException e) {log.error("StandardPipeline.setBasic: stop", e);}}if (oldBasic instanceof Contained) {try {((Contained) oldBasic).setContainer(null);} catch (Throwable t) {ExceptionUtils.handleThrowable(t);}}}// Start the new component if necessaryif (valve == null)return;if (valve instanceof Contained) {((Contained) valve).setContainer(this.container);}if (getState().isAvailable() && valve instanceof Lifecycle) {try {((Lifecycle) valve).start();} catch (LifecycleException e) {log.error("StandardPipeline.setBasic: start", e);return;}}// Update the pipelineValve current = first;while (current != null) {if (current.getNext() == oldBasic) {current.setNext(valve);break;}current = current.getNext();}this.basic = valve;}//3333333333333333333 @Override public void addValve(Valve valve) {// Validate that we can add this Valveif (valve instanceof Contained)((Contained) valve).setContainer(this.container);// Start the new component if necessaryif (getState().isAvailable()) {if (valve instanceof Lifecycle) {try {((Lifecycle) valve).start();} catch (LifecycleException e) {log.error("StandardPipeline.addValve: start: ", e);}}}// Add this Valve to the set associated with this Pipelineif (first == null) {first = valve;valve.setNext(basic);} else {Valve current = first;while (current != null) {if (current.getNext() == basic) {current.setNext(valve);valve.setNext(basic);break;}current = current.getNext();}}container.fireContainerEvent(Container.ADD_VALVE_EVENT, valve); }//44444444444 @Override public Valve[] getValves() {ArrayList<Valve> valveList = new ArrayList<Valve>();Valve current = first;if (current == null) {current = basic;}while (current != null) {valveList.add(current);current = current.getNext();}return valveList.toArray(new Valve[0]);}//5555555555555555 @Override public void removeValve(Valve valve) {Valve current;if(first == valve) {first = first.getNext();current = null;} else {current = first;}while (current != null) {if (current.getNext() == valve) {current.setNext(valve.getNext());break;}current = current.getNext();}if (first == basic) first = null;if (valve instanceof Contained)((Contained) valve).setContainer(null);if (valve instanceof Lifecycle) {// Stop this valve if necessaryif (getState().isAvailable()) {try {((Lifecycle) valve).stop();} catch (LifecycleException e) {log.error("StandardPipeline.removeValve: stop: ", e);}}try {((Lifecycle) valve).destroy();} catch (LifecycleException e) {log.error("StandardPipeline.removeValve: destroy: ", e);}}container.fireContainerEvent(Container.REMOVE_VALVE_EVENT, valve); }//666666666666@Overridepublic Valve getFirst() {if (first != null) {return first;}return basic;} }

在StandardPipeline標(biāo)準(zhǔn)實(shí)現(xiàn)類中我們看到了對(duì)Pipeline接口的實(shí)現(xiàn)，我們選了幾個(gè)比較重要的方法做源碼的解析。

方法1是startInternal()

//1111111111 @Override protected synchronized void startInternal() throws LifecycleException {// Start the Valves in our pipeline (including the basic), if anyValve current = first;if (current == null) {current = basic;}while (current != null) {if (current instanceof Lifecycle)((Lifecycle) current).start();current = current.getNext();}setState(LifecycleState.STARTING); }

組件的start()方法，將first(第一個(gè)閥門(mén))賦值給current變量，如果current為空，就將basic(也就是基礎(chǔ)閥)賦值給current,接下來(lái)如果一個(gè)標(biāo)準(zhǔn)的遍歷單向鏈表，調(diào)用每個(gè)對(duì)象的start()方法，最后將組件(pipeline)狀態(tài)設(shè)置為STARTING(啟動(dòng)中)。

方法2

//2222222222222222222222 @Override public void setBasic(Valve valve) {// Change components if necessary //如果已經(jīng)有基礎(chǔ)閥(basic已經(jīng)有值并且跟要設(shè)置的值一樣）那么直接return Valve oldBasic = this.basic; if (oldBasic == valve)return;// Stop the old component if necessary //舊的基礎(chǔ)閥非空 那么調(diào)用其stop方法取消和對(duì)應(yīng)container的關(guān)聯(lián)。(銷毀舊的基礎(chǔ)閥) if (oldBasic != null) {if (getState().isAvailable() && (oldBasic instanceof Lifecycle)) {try {((Lifecycle) oldBasic).stop();} catch (LifecycleException e) {log.error("StandardPipeline.setBasic: stop", e);}}if (oldBasic instanceof Contained) {try {((Contained) oldBasic).setContainer(null);} catch (Throwable t) {ExceptionUtils.handleThrowable(t);}} }// Start the new component if necessary //非空判斷 if (valve == null)return; //和Container進(jìn)行關(guān)聯(lián) if (valve instanceof Contained) {((Contained) valve).setContainer(this.container); } //啟動(dòng)新的閥門(mén) if (getState().isAvailable() && valve instanceof Lifecycle) {try {((Lifecycle) valve).start();} catch (LifecycleException e) {log.error("StandardPipeline.setBasic: start", e);return;} } //遍歷閥門(mén)鏈表將新的閥門(mén)取代舊的閥門(mén) // Update the pipeline Valve current = first; while (current != null) {if (current.getNext() == oldBasic) {current.setNext(valve);break;}current = current.getNext(); } //將基礎(chǔ)閥設(shè)置為新的閥門(mén) this.basic = valve;}

方法2是用來(lái)設(shè)置基礎(chǔ)閥的方法，這個(gè)方法在每個(gè)容器的構(gòu)造函數(shù)中調(diào)用，代碼邏輯也比較簡(jiǎn)單，稍微注意的地方就是閥門(mén)鏈表的遍歷。

方法3

//3333333333333333333 @Override public void addValve(Valve valve) {// Validate that we can add this Valve// 驗(yàn)證Valve 關(guān)聯(lián)Containerif (valve instanceof Contained)((Contained) valve).setContainer(this.container);// Start the new component if necessary// 驗(yàn)證組件狀態(tài)，如果對(duì)的話 啟動(dòng)需要添加的Valve，調(diào)用start方法。if (getState().isAvailable()) {if (valve instanceof Lifecycle) {try {((Lifecycle) valve).start();} catch (LifecycleException e) {log.error("StandardPipeline.addValve: start: ", e);}}}//如果 first變量為空，將valve賦值給first變量，并且設(shè)置 valve的下一個(gè)閥門(mén)為基礎(chǔ)閥//之所以這樣是因?yàn)?#xff0c;如果first為空說(shuō)明這個(gè)容器只有一個(gè)基礎(chǔ)閥，所以此次添加的閥門(mén)肯定是第一個(gè)非基礎(chǔ)閥閥門(mén)// Add this Valve to the set associated with this Pipelineif (first == null) {first = valve;valve.setNext(basic);} else {//否則 遍歷閥門(mén)鏈表，將要被添加的閥門(mén)設(shè)置在 基礎(chǔ)閥之前。Valve current = first;while (current != null) {if (current.getNext() == basic) {current.setNext(valve);valve.setNext(basic);break;}current = current.getNext();}}//container觸發(fā)添加閥門(mén)事件container.fireContainerEvent(Container.ADD_VALVE_EVENT, valve); }

這方法是像容器中添加Valve，在server.xml解析的時(shí)候也會(huì)調(diào)用該方法，具體代碼可以到Digester相關(guān)的文章中尋找。

方法4

//44444444444 @Override public Valve[] getValves() {ArrayList<Valve> valveList = new ArrayList<Valve>();Valve current = first;if (current == null) {current = basic;}while (current != null) {valveList.add(current);current = current.getNext();}return valveList.toArray(new Valve[0]);}

獲取所有的閥門(mén),其實(shí)就是將閥門(mén)鏈表添加到一個(gè)集合內(nèi)，最后轉(zhuǎn)成數(shù)組返回。

方法5

//5555555555555555 @Override public void removeValve(Valve valve) {Valve current;//如果first 是需要被移除的valve 那么將first的下一個(gè)閥門(mén)賦值給first//并且current 賦值null,否則current 賦值firstif(first == valve) {first = first.getNext();current = null;} else {current = first;}//遍歷閥門(mén)鏈表 查找需要被移除的閥門(mén)//如果之前first是被移除的話 current = null是不會(huì)進(jìn)入該循環(huán)while (current != null) {if (current.getNext() == valve) {current.setNext(valve.getNext());break;}current = current.getNext();}//如果first（此時(shí)已經(jīng)指向下一個(gè)閥門(mén)）此時(shí) == 基礎(chǔ)閥，那么first置空//從這里可以看出來(lái) first指的是第一個(gè)閥門(mén)，即使整個(gè)container只有一個(gè)基礎(chǔ)閥門(mén)也不會(huì)指向基礎(chǔ)閥。//first嚴(yán)格定義是 除了基礎(chǔ)閥的第一個(gè)閥門(mén)。if (first == basic) first = null;//驗(yàn)證需要被移除的閥門(mén) 取消container關(guān)聯(lián)if (valve instanceof Contained)((Contained) valve).setContainer(null);//調(diào)用閥門(mén)的生命周期 stop destroy 方法。if (valve instanceof Lifecycle) {// Stop this valve if necessaryif (getState().isAvailable()) {try {((Lifecycle) valve).stop();} catch (LifecycleException e) {log.error("StandardPipeline.removeValve: stop: ", e);}}try {((Lifecycle) valve).destroy();} catch (LifecycleException e) {log.error("StandardPipeline.removeValve: destroy: ", e);}}//觸發(fā)container的移除valve事件。container.fireContainerEvent(Container.REMOVE_VALVE_EVENT, valve); }

方法666666

//666666666666 @Override public Valve getFirst() {if (first != null) {return first;}return basic; }

在方法5中我們也看到了，first指向的是容器第一個(gè)非基礎(chǔ)閥門(mén)的閥門(mén)，從方法6中也可以看出來(lái)，first在只有一個(gè)基礎(chǔ)閥的時(shí)候并不會(huì)指向基礎(chǔ)閥，因?yàn)槿绻赶蚧A(chǔ)閥的話就不需要判斷非空然后返回基礎(chǔ)閥了，這是個(gè)需要注意的點(diǎn)！

關(guān)于tomcat的pipeline機(jī)制就講那么多，其實(shí)涉及的非常基礎(chǔ)，最關(guān)鍵的pipeline的invoke()方法也沒(méi)有看，主要invoke()方法和其他的點(diǎn)比較重復(fù)，準(zhǔn)備還是放到請(qǐng)求在容器中的流轉(zhuǎn)講解！敬請(qǐng)期待！

轉(zhuǎn)載于:https://www.cnblogs.com/coldridgeValley/p/5816414.html

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