2）以上4中容器都是 org.apache.catalina包下的接口：分别为Engine，Host， Context， Wrapper，他们都继承自Container接口。这4个接口的标准实现是 StandardEngine类，StandardHost类，StandardContext类，StandardWrapper类，他们都在 org.apache.catalina.core 包内；

Attention）

【2】管道任务

1）本节旨在说明：当连接器调用了servlet容器的invoke方法后会发生什么事情，并讨论org.apache.catalina 包中的4个相关接口，Pipeline， Valve， ValveContext 和 Contained；

2）管道和阀：

2.1）管道：包含该servlet容器将要调用的任务；

2.2）一个阀：表示一个具体的任务。

2.3）在servlet容器的管道中，有一个基础阀，但是，可以添加任意数量的阀。阀的数量指的是额外添加的阀数量，即，不包括基础阀。有意思的是， 可以通过编辑tomcat 的 配置文件(server.xml)来动态地添加阀；

2.4）一条管道和阀的示意图如下：

Attention）

3）管道的invoke方法：一个servlet容器可以有一条管道，当调用了容器的invoke方法后，容器会将处理工作交由管道完成，而管道会调用其中的第一个阀开始处理。当第一个阀处理完后，它会调用后续的阀继续执行任务，直到管道中所有的阀都处理完成。下面是invoke方法的伪代码：

import java.io.IOException;
import java.io.PrintWriter;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.Locale;
import java.util.ResourceBundle;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.Locale;
import java.util.ResourceBundle;

// invoke each valve added to the pipeline，先是非基础阀调用 invoke方法
for(;;){valve[i].invoke();
}
// then, invoke the basic valve， 后是基础阀调用 invoke方法（基础阀最后一个调用invoke方法）
basicValve.invoke(...);public void invoke(Request request, Response response) // SimplePipeline.invoke()throws IOException, ServletException {// Invoke the first Valve in this pipeline for this request(new SimplePipelineValveContext()).invokeNext(request, response);}
public void invokeNext(Request request, Response response) // SimplePipeline.invokeNext()throws IOException, ServletException {int subscript = stage;stage = stage + 1;// Invoke the requested Valve for the current request threadif (subscript < valves.length) {valves[subscript].invoke(request, response, this);}else if ((subscript == valves.length) && (basic != null)) {basic.invoke(request, response, this);}else {throw new ServletException("No valve");}}} // end of inner class

4）实现阀的遍历：Tomcat引入接口 org.apache.catalina.ValveContext 来实现阀的遍历执行；

4.1）管道必须保证添加到其中的所有阀和基础阀都被调用一次：这是通过调用一个 ValveContext接口实例来实现的。

4.2）ValveContext接口中最重要的方法是 invokeNext方法：在创建了ValveContext实例后，管道会调用ValveContext实例的 invokeNext方法。ValveContext实例会首先调用管道中的 第一个阀，第一个阀执行完后，会调用后面的阀继续执行。ValveContext实例会将自身传给每个阀，因此，每个阀都可以调用 ValveContext实例的 invokeNext方法；

5）org.apache.catalina.core.StandardPipeline类：是所有servlet容器中的Pipeline接口的实现，Tomcat4中有一个实现了ValveContext接口的内部类，名为StandardPipelineValveContext；

6）Tomcat5 从 StandardPipeline类中移除了 StandardPipelineValveContext类：却使用 org.apache.catalina.core.StandardValveContext类来调用阀；

【2.1】Pipeline接口

1）对于Pipeline接口：首先要提到的一个方法是 invoke方法，servlet容器调用invoke方法来开始调用管道中的阀和基础阀；

public interface Pipeline {public Valve getBasic();public void setBasic(Valve valve);public void addValve(Valve valve);public Valve[] getValves(); public void invoke(Request request, Response response) throws IOException, ServletException;public void removeValve(Valve valve);
} 

2）getBasic和setBasic：setBasic方法将基础阀设置到管道中，getBasic获取基础阀；（干货——管道中可以指定基础阀）

3）addValve和removeValve：新增阀和删除阀；（干货——在管道中可以新增和删除非基础阀）

【2.2】Valve接口

1）阀是Valve接口的实例，用来处理接收到的请求，有两个方法：invoke方法和getinfo方法；

【2.3.】ValveContext接口

1）有两个方法：invokeNext方法和 getInfo方法；

【2.4】Contained接口

public interface Contained {   public Container getContainer();public void setContainer(Container container);
} 

【3】Wrapper接口

1）intro to Wrapper： Wrapper级的servlet容器是一个 org.apache.catalina.Wrapper接口的实例，表示一个独立的servlet定义。Wrapper接口继承自 Container接口，又添加了一些额外的方法。

public interface Wrapper extends Container {     public long getAvailable();public void setAvailable(long available);public String getJspFile(); public void setJspFile(String jspFile); public int getLoadOnStartup(); public void setLoadOnStartup(int value); public String getRunAs(); public void setRunAs(String runAs); public String getServletClass(); public void setServletClass(String servletClass); public boolean isUnavailable(); public void addInitParameter(String name, String value);     public void addInstanceListener(InstanceListener listener);     public void addSecurityReference(String name, String link);     public Servlet allocate() throws ServletException;     public void deallocate(Servlet servlet) throws ServletException;     public String findInitParameter(String name);    public String[] findInitParameters();     public String findSecurityReference(String name);     public String[] findSecurityReferences();    public void load() throws ServletException;    public void removeInitParameter(String name); public void removeInstanceListener(InstanceListener listener);     public void removeSecurityReference(String name);  public void unavailable(UnavailableException unavailable);   public void unload() throws ServletException;
}

2）Wrapper接口的实现类：要负责管理继承servlet类的servlet生命周期，即，调用 servlet的 init(), service(), destroy()方法；

3）由于Wrapper已经是最低级的容器了，不能再向其中添加子容器；（干货——Wrapper已经是最低级的servlet容器）

4）Wrapper接口有两个方法：load方法 和 allocate方法；

4.1）load方法：载入并初始化servlet类；

4.2）allocate方法：会分配一个已经初始化的servlet实例；

【4】Context接口

1）intro to Context：Context接口是一个web 应用程序，一个Context实例可以有一个或多个Wrapper实例作为其子容器；

2）比较重要的方法： addWrapper() and createWrapper()；

【5】Wrapper 应用程序（demonstrate how to build a smallest servlet container）

1）SimpleWrapper类：该类实现了Wrapper接口，包含一个Pipeline实例，并使用Loader实例载入servlet类。Pipeline实例包含一个基础阀和两个额外的阀。

【5.1】SimpleLoader类

1）SimpleLoader：负责完成类的载入工作，它知道servlet类的位置，通过调用其getClassLoader可以返回一个 java.lang.ClassLoader实例，可以用来搜索servlet类的位置；

2）SimpleLoader的构造函数：会初始化类加载器，供 SimpleWrapper实例使用；

public class SimpleLoader implements Loader {public static final String WEB_ROOT =System.getProperty("user.dir") + File.separator  + "webroot";ClassLoader classLoader = null;Container container = null;public SimpleLoader() {try {URL[] urls = new URL[1];URLStreamHandler streamHandler = null;File classPath = new File(WEB_ROOT);String repository = (new URL("file", null, classPath.getCanonicalPath() + File.separator)).toString() ;urls[0] = new URL(null, repository, streamHandler);classLoader = new URLClassLoader(urls);}catch (IOException e) {System.out.println(e.toString() );}}

【5.2】SimplePipeline类

1）该类最重要的方法是 invoke方法；

public class SimplePipeline implements Pipeline {public SimplePipeline(Container container) {setContainer(container);}// The basic Valve (if any) associated with this Pipeline.protected Valve basic = null;// The Container with which this Pipeline is associated.protected Container container = null;// the array of Valvesprotected Valve valves[] = new Valve[0];public void setContainer(Container container) {this.container = container;}public Valve getBasic() {return basic;}public void setBasic(Valve valve) {this.basic = valve;((Contained) valve).setContainer(container);}public void addValve(Valve valve) {if (valve instanceof Contained)((Contained) valve).setContainer(this.container);synchronized (valves) {Valve results[] = new Valve[valves.length +1];System.arraycopy(valves, 0, results, 0, valves.length);results[valves.length] = valve;valves = results;}}public Valve[] getValves() {return valves;}public void invoke(Request request, Response response)throws IOException, ServletException {// Invoke the first Valve in this pipeline for this request(new SimplePipelineValveContext()).invokeNext(request, response);}public void removeValve(Valve valve) {}// this class is copied from org.apache.catalina.core.StandardPipeline class's// StandardPipelineValveContext inner class.protected class SimplePipelineValveContext implements ValveContext {protected int stage = 0;public String getInfo() {return null;}public void invokeNext(Request request, Response response)throws IOException, ServletException {int subscript = stage;stage = stage + 1;// Invoke the requested Valve for the current request threadif (subscript < valves.length) {valves[subscript].invoke(request, response, this);}else if ((subscript == valves.length) && (basic != null)) {basic.invoke(request, response, this);}else {throw new ServletException("No valve");}}} // end of inner class
}

【5.3】SimpleWrapper类

1）该类实现了Wrapper接口：并提供了 allocate 和 load 方法的实现；

2）getLoader()方法：该方法返回一个用于载入servlet 类的载入器。若Wrapper实例已经关联了一个载入器，则直接将其返回；否则，它将返回父容器的载入器。若没有父容器，getLoader方法会返回null；

3）SimpleWrapper类：有一个Pipeline实例，并该为Pipeline实例设置基础阀；

public class SimpleWrapper implements Wrapper, Pipeline {// the servlet instanceprivate Servlet instance = null;private String servletClass;private Loader loader;private String name;private SimplePipeline pipeline = new SimplePipeline(this);protected Container parent = null;public SimpleWrapper() {pipeline.setBasic(new SimpleWrapperValve());}public synchronized void addValve(Valve valve) {pipeline.addValve(valve);}public Servlet allocate() throws ServletException {// Load and initialize our instance if necessaryif (instance==null) {try {instance = loadServlet();}catch (ServletException e) {throw e;}catch (Throwable e) {throw new ServletException("Cannot allocate a servlet instance", e);}}return instance;}private Servlet loadServlet() throws ServletException {if (instance!=null)return instance;Servlet servlet = null;String actualClass = servletClass;if (actualClass == null) {throw new ServletException("servlet class has not been specified");}Loader loader = getLoader();// Acquire an instance of the class loader to be usedif (loader==null) {throw new ServletException("No loader.");}ClassLoader classLoader = loader.getClassLoader();// Load the specified servlet class from the appropriate class loaderClass classClass = null;try {if (classLoader!=null) {classClass = classLoader.loadClass(actualClass);}}catch (ClassNotFoundException e) {throw new ServletException("Servlet class not found");}// Instantiate and initialize an instance of the servlet class itselftry {servlet = (Servlet) classClass.newInstance();}catch (Throwable e) {throw new ServletException("Failed to instantiate servlet");}// Call the initialization method of this servlettry {servlet.init(null);}catch (Throwable f) {throw new ServletException("Failed initialize servlet.");}return servlet;}public String getInfo() {return null;}public Loader getLoader() {if (loader != null)return (loader);if (parent != null)return (parent.getLoader());return (null);}

【5.4】SimpleWrapperValve类

1）SimpleWrapperValve是一个基础阀：用于处理读iSimpleWrapper类的请求，其最主要的方法是 invoke方法；

public class SimpleWrapperValve implements Valve, Contained {protected Container container;public void invoke(Request request, Response response, ValveContext valveContext)throws IOException, ServletException {SimpleWrapper wrapper = (SimpleWrapper) getContainer();ServletRequest sreq = request.getRequest();ServletResponse sres = response.getResponse();Servlet servlet = null;HttpServletRequest hreq = null;if (sreq instanceof HttpServletRequest)hreq = (HttpServletRequest) sreq;HttpServletResponse hres = null;if (sres instanceof HttpServletResponse)hres = (HttpServletResponse) sres;// Allocate a servlet instance to process this requesttry {servlet = wrapper.allocate();if (hres!=null && hreq!=null) {servlet.service(hreq, hres);}else {servlet.service(sreq, sres);}}catch (ServletException e) {}}public String getInfo() {return null;}public Container getContainer() {return container;}public void setContainer(Container container) {this.container = container;}
}

【5.5】ClientIPLoggerValve类

1）ClientIPLoggerValve类所表示的阀：用来将client的IP 地址输出到控制台上；

2）注意其invoke方法：它先调用方法参数 valveContext的 invokeNext方法来调用管道中的下一个阀。然后，它会把几行字符串output到 console；

public class ClientIPLoggerValve implements Valve, Contained {protected Container container;public void invoke(Request request, Response response, ValveContext valveContext)throws IOException, ServletException {// Pass this request on to the next valve in our pipelinevalveContext.invokeNext(request, response);System.out.println("Client IP Logger Valve");ServletRequest sreq = request.getRequest();System.out.println(sreq.getRemoteAddr());System.out.println("------------------------------------");}public String getInfo() {return null;}public Container getContainer() {return container;}public void setContainer(Container container) {this.container = container;}
}

【5.6】HeaderLoggerValve类

1）HeaderLoggerValve类作用：会把请求头信息output到 console；

2）注意其invoke方法：它先调用方法参数 valveContext的 invokeNext方法来调用管道中的下一个阀。

public class HeaderLoggerValve implements Valve, Contained {protected Container container;public void invoke(Request request, Response response, ValveContext valveContext)throws IOException, ServletException {// Pass this request on to the next valve in our pipelinevalveContext.invokeNext(request, response);System.out.println("Header Logger Valve");ServletRequest sreq = request.getRequest();if (sreq instanceof HttpServletRequest) {HttpServletRequest hreq = (HttpServletRequest) sreq;Enumeration headerNames = hreq.getHeaderNames();while (headerNames.hasMoreElements()) {String headerName = headerNames.nextElement().toString();String headerValue = hreq.getHeader(headerName);System.out.println(headerName + ":" + headerValue);}}elseSystem.out.println("Not an HTTP Request");System.out.println("------------------------------------");}public String getInfo() {return null;}public Container getContainer() {return container;}public void setContainer(Container container) {this.container = container;}
}

【5.7】Bootstrap1

Attention）我这里总结了该测试用例的调用流程图

【5.8】运行应用程序

1）运行参数

E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot com.tomcat.chapter5.startup/Bootstrap1
HttpConnector Opening server socket on all host IP addresses
HttpConnector[8080] Starting background thread
ModernServlet -- init
Client IP Logger Valve
127.0.0.1
------------------------------------
Header Logger Valve
host:localhost:8080
connection:keep-alive
accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
user-agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36
accept-encoding:gzip, deflate, sdch
accept-language:zh-CN,zh;q=0.8,en;q=0.6
------------------------------------
Client IP Logger Valve
127.0.0.1
------------------------------------
Header Logger Valve
host:localhost:8080
connection:keep-alive
accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
user-agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36
accept-encoding:gzip, deflate, sdch
accept-language:zh-CN,zh;q=0.8,en;q=0.6
------------------------------------

2）运行结果

 

【6.1】SimpleContextValve类

1）该类是 SimleContext的基础阀，最重要的方法是invoke方法；

【6.2】SimpleContextMapper类

public class SimpleContextMapper implements Mapper {/*** The Container with which this Mapper is associated.*/private SimpleContext context = null;public Container getContainer() {return (context);}public void setContainer(Container container) {if (!(container instanceof SimpleContext))throw new IllegalArgumentException("Illegal type of container");context = (SimpleContext) container;}public String getProtocol() {return null;}public void setProtocol(String protocol) {}/*** Return the child Container that should be used to process this Request,* based upon its characteristics.  If no such child Container can be* identified, return <code>null</code> instead.** @param request Request being processed* @param update Update the Request to reflect the mapping selection?** @exception IllegalArgumentException if the relative portion of the*  path cannot be URL decoded*/public Container map(Request request, boolean update) {// Identify the context-relative URI to be mappedString contextPath =((HttpServletRequest) request.getRequest()).getContextPath();String requestURI = ((HttpRequest) request).getDecodedRequestURI();String relativeURI = requestURI.substring(contextPath.length());// Apply the standard request URI mapping rules from the specificationWrapper wrapper = null;String servletPath = relativeURI;String pathInfo = null;String name = context.findServletMapping(relativeURI);if (name != null)wrapper = (Wrapper) context.findChild(name);return (wrapper);}
}

1）map方法需要两个参数：一个request对象和一个布尔变量。

2）在本app中， 忽略了第2个参数。map() 方法：会从request对象中解析出请求的上下文路径，并调用 Conetext 实例的findServletMapping() 方法 来获取一个与该路径相关联的名称，如果找到了这个名称，则它调用 Context实例的findChild方法获取一个 Wrapper 实例；

【6.3】SimpleContext类

【6.5】运行应用程序

1）运行参数

E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\src>java -cp .;lib/servlet.jar;lib/catalina_4_1_24.jar;E:\bench-cluster\cloud-data-preprocess\HowTomcatWorks\webroot  com.tomcat.chapter5.startup.
Bootstrap2
HttpConnector Opening server socket on all host IP addresses
HttpConnector[8080] Starting background thread
Client IP Logger Valve
127.0.0.1
------------------------------------
Header Logger Valve
host:localhost:8080
connection:keep-alive
accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
user-agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.71 Safari/537.36
accept-encoding:gzip, deflate, sdch
accept-language:zh-CN,zh;q=0.8,en;q=0.6
------------------------------------
init
from service
Client IP Logger Valve
127.0.0.1
------------------------------------

2）运行结果