How Tomcat works 4-5: Container

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本文详细解析了Tomcat容器的内部结构，包括Engine、Host、Context和Wrapper等关键概念，探讨了它们之间的关系及如何通过Pipeline机制执行请求处理流程。同时，介绍了自定义Valve实现特定功能的方法。

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Container概述

（1）主要包含四种：Engine：整个catalina servlet容器, Host：一个虚拟主机包含多个context容器, Context：一个web应用容器，包含一道多个Wrapper容器, Wrapper：独立servlet容器

（2）UML图

（3）添加/移除/查找子容器：

container.addChild(container) -> container.removeChild(container)->container.findChild(name)->Container[] container.findChildren

（4）包含组件：Loader/Logger/Manager/Realm

Pipeline任务：

Tomcat启动时通过读取server.xml的配置决定使用哪个容器来执行，其中原理运用pipeline技术

pipeline任务重要的四个接口：pipeline/valve/valveContext/Contained

Pipeline interface code:

public interface Pipeline {
Valve getBasic();

void setBasic(Valve basic);

void addValves(Valve valve);

Valve[] getValves();

void removeValves();

void invoke(Request request, Response response) throws IOException,ServletException;

}

Valve interface code:

public interface Valve {

String getInfo();

void invoke(Request request, Response response, VavleContext context) throws IOException, ServletException;

}

ValveContext interface code:

public interface ValveContext {

String getInfo();

void invokeNext(Request request, Response response) throws IOException, ServletException;

}

Wrapper接口：

（1）wrapper的实现类作用：

用于管理独立servlet类的lifecycle，调用servlet的init, destroy, service方法。wrapper处于容器层次底部，不能添加子容器

（2）重要方法

public interface Wrapper {

Servlet allocate() throws ServletException; // 是否实现SingleThreadModel

void load() throws ServletException; // 加载和初始化servlet实例

}

Wrapper容器应用实例：

业务流程图：

（1）UML结构图

（2）SimpleWrapperLoader code:

public class SimpleWrapperLoader implements Loader{

URLClassLoader loader = null;

Container container = null;

public SimpleWrapperLoader() {

// 实现URL class loader

try {

URL[] urls = new URL[1];

URLStreamHandler streamHandler = null;

File classPath = new File(Constants.WEB_SERVLET_ROOT);



// 从org.apache.catalina.loader.StandardClassLoader/startup.ClassLoaderFactory中获取该code

String repository = (new URL("file", null, classPath.getCanonicalPath()+File.separator)).toString();

urls[0] = new URL(null, repository, streamHandler);

loader = new URLClassLoader(urls);                        

}catch (IOException e) {

System.out.println(e.toString());

}

}

（3）SimplePipeline code:

package com.cisco.tomcat.container;



import java.io.IOException;

import javax.servlet.ServletException;

import org.apache.catalina.Container;

import org.apache.catalina.connector.Request;

import org.apache.catalina.connector.Response;



public class SimplePipeline implements Pipeline {

Valve basic;

Valve[] valves;

Container container;



public SimplePipeline(Container container) {

this.container = container;

}



@Override

public Valve getBasic() {

return basic;

}



@Override

public void setBasic(Valve basic) {

this.basic = basic;

((Contained)basic).setContainer(container);

}



@Override

public void addValves(Valve valve) {

if(valve instanceof Contained) {

((Contained)valve).setContainer(container);

}

synchronized (valves) {

Valve results[] = new Valve[valves.length+1];

System.arraycopy(valves,0, results, 0, valves.length);

results[valves.length] = valve;

valves = results;

}



}



@Override

public Valve[] getValves() {

return valves;

}



@Override

public void removeValves() {                

}



@Override

public void invoke(Request request, Response response) throws IOException, ServletException {

// 调用内部类的StandardValveContext的invokeNext方法，内部会调用每个valves的invoke方法

// 在调用的valve中会继续调用valveContext.invokeNext的方法，然后调用自身的动作，实现pipeline的所有动作

(new StandardValveContext()).invokeNext(request, response);

}



protected class StandardValveContext implements ValveContext{

int stage = 0;

@Override

public String getInfo() {

return null;

}



@Override

public void invokeNext(Request request, Response response) throws IOException, ServletException {

int subscript = stage;

stage = stage + 1;

if(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 valves");

}

}



}



}

（4）SimpleWrapperValve：代表basic valve，所以只需要执行加载执行servlet动作，无需调用valveContext.invokeNext()

Code:

package com.cisco.tomcat.container;



import java.io.IOException;



import javax.servlet.Servlet;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import org.apache.catalina.Container;

import org.apache.catalina.connector.Request;

import org.apache.catalina.connector.Response;



public class SimpleWrapperValve implements Valve,  Contained  {



protected Container container;

@Override

public String getInfo() {

System.out.println("this is SimpleWrapperValve");

return null;

}



@Override

public void invoke(Request request, Response response, ValveContext context) throws IOException, ServletException {

SimpleWrapper wrapper = (SimpleWrapper)getContainer();

ServletRequest sreq = request.getRequest();

ServletResponse sresp = response.getResponse();

HttpServletRequest hreq = null;

HttpServletResponse hresp = null;

Servlet servlet = null;

if(sreq instanceof HttpServletRequest) {

hreq = (HttpServletRequest)sreq;

}

if(sresp instanceof HttpServletResponse) {

hresp = (HttpServletResponse) sresp;

}

try {

servlet = wrapper.allocate();

if(hreq!=null && hresp!=null) {

servlet.service(hreq, hresp);

}else {

servlet.service(sreq, sresp);

}                        

}catch(ServletException e) {



}





}



@Override

public void setContainer(Container container) {

this.container = container;                

}



@Override

public Container getContainer() {

return container;

}



}

（5）ClientIPValve:

添加的addition valve. 实现打印client ip功能：首先调用context.invokeNext()，然后执行自身动作

Code:

package com.cisco.tomcat.container;



import java.io.IOException;



import javax.servlet.Servlet;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;



import org.apache.catalina.Container;

import org.apache.catalina.connector.Request;

import org.apache.catalina.connector.Response;



public class ClientIPValve implements Valve, Contained{



private Container container;

@Override

public void setContainer(Container container) {

this.container = container;

}



@Override

public Container getContainer() {

return container;

}



@Override

public String getInfo() {

return null;

}



@Override

public void invoke(Request request, Response response, ValveContext context) throws IOException, ServletException {

context.invokeNext(request, response);

System.out.println("ClinetIP Valve invoke method...");

ServletRequest sreq = request.getRequest();

System.out.println("IP:"+sreq.getRemoteAddr());

}



}

（6）HeaderLoggerValve

添加的addition valve.实现打印header功能，首先调用context.invokeNext()。然后执行自身动作

package com.cisco.tomcat.container;



import java.io.IOException;

import java.util.Enumeration;



import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;



import org.apache.catalina.Container;

import org.apache.catalina.connector.Request;

import org.apache.catalina.connector.Response;



public class HeaderLoggerValve implements Valve, Contained{



private Container container;

@Override

public void setContainer(Container container) {

this.container = container;

}



@Override

public Container getContainer() {

return container;

}



@Override

public String getInfo() {

return null;

}



@Override

public void invoke(Request request, Response response, ValveContext context) throws IOException, ServletException {

context.invokeNext(request, response);

System.out.println("打印Http Header日志......");

if(request instanceof HttpServletRequest){

HttpServletRequest hreq = (HttpServletRequest) request;

Enumeration<String> headerNames = hreq.getHeaderNames();

while (headerNames.hasMoreElements()) {

String headerName = headerNames.nextElement().toString();

String headerValue = hreq.getHeader(headerName);

System.out.println(headerName + ": " + headerValue);

}

}else {

System.out.println("没有Header");

}



}



}

（7）BootStrap类：

package com.cisco.tomcat.container;



import java.io.IOException;



import org.apache.catalina.Loader;



public class Bootstrap {

public static void main(String[] args) {

Wrapper wrapper = new SimpleWrapper();

Loader loader = new SimpleWrapperLoader();

wrapper.setLoader(loader);

Valve clientIpValve = new ClientIPValve();

Valve headerLoggerValve = new HeaderLoggerValve();

wrapper.addValves(clientIpValve);

wrapper.addValves(headerLoggerValve);

wrapper.setServletClass("PrimitiveServlet");



HttpConnector connector = new HttpConnector();

connector.setContainer(wrapper);



connector.initialize();

connector.start();



try {

System.in.read();

} catch (IOException e) {

e.printStackTrace();

}

}

}