一、Tomcat底层整体架构

1.简介 :

2.分析图 :

3.基于Socket开发服务端的流程 :

4.打通服务器端和客户端的数据通道 :

二、多线程模型的实现

1.思路分析 :

2.处理HTTP请求 :

3.自定义Tomcat :

三、自定义Servlet规范

1. HTTP请求和响应 :

1° CyanServletRequest

2° CyanServletResponse

2.Servlet规范 :

1° CyanServlet

2° CyanHttpServlet

3° CyanLoginServlet

3.容器实现 :

1° 思路分析

2° web.xml配置文件

3° 最终版自定义Tomcat

4° 最终版自定义线程类

5° 容器启动测试

一、Tomcat底层整体架构

1.简介 :

Tomcat 有三种运行模式 (BIO[阻塞], NIO[非阻塞], APR)，这里采用 BIO 线程模型来模拟实现。

2.分析图 :

如下图所示 :

浏览器请求servlet资源后，Tomcat底层会通过Socket网络编程来接收请求，每次请求，都会创建一个新的线程去调用相应的Web资源，并返回。

3.基于Socket开发服务端的流程 :

如下图所示 :

通过获取的Socket对象，来获取Socket对象对应的字节输入流和字节输出流。
可以利用对象转换流将字节流转换为字符流对象(InputStreamReader实现了Reader抽象类)，然后再通过BufferedReader的包装，将节点流转换成包装流(处理流)。

4.打通服务器端和客户端的数据通道 :

PS :
Maven配置Web应用，运行出现jakarta.servlet.ServletException:
因为tomcat10之后不是javax.servlet，而是jakarta.servlet，所以Web的依赖应该换成如下所示 : (pom.xml配置文件）

<!--jar包的依赖--><dependency><groupId>jakarta.servlet</groupId><artifactId>jakarta.servlet-api</artifactId><version>5.0.0</version><scope>provided</scope></dependency><!--jsp的依赖--><dependency><groupId>jakarta.servlet.jsp</groupId><artifactId>jakarta.servlet.jsp-api</artifactId><version>3.0.0</version><scope>provided</scope></dependency>

MyTomcat类代码如下 : （服务端；自定义的Tomcat)

package tomcat;import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;/**服务器端*/
public class MyTomcat {public static void main(String[] args) throws IOException {ServerSocket serverSocket = new ServerSocket(8080);System.out.println("Tomcat在8080端口进行监听...");System.out.println("--------------------------------------");while (!serverSocket.isClosed()) {//获取Socket对象Socket socket = serverSocket.accept();//接收来自浏览器端的信息InputStream inputStream = socket.getInputStream();BufferedReader bufferedReader =new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));String content = null;  //局部变量在使用前必须赋初值。while ((content = bufferedReader.readLine()) != null) {//判断content是否是空串儿if (content.length() == 0) {break;}System.out.println(content);}//服务器向浏览器回送消息OutputStream outputStream = socket.getOutputStream();//设置一个HTTP响应包的响应头// "/r/n"表示换行String respHeader ="HTTP/1.1 200\r\n" +"Content-Type: text/html;charset=utf-8\r\n\r\n";//设置HTTP响应的响应体String respBody = respHeader + "<h1>你好！</h1>";/*注意这里不能使用字符包装流来写数据!!!。*/outputStream.write(respBody.getBytes());System.out.println("--------------------------------------");System.out.println(respBody);//释放资源outputStream.flush();outputStream.close();inputStream.close();socket.close();
//            serverSocket.close();}}
}

在浏览器地址栏访问本机8080端口。
login.html代码如下 :

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>login</title><style>table, tr, td {border:2px cornflowerblue solid;border-collapse: collapse;padding: 10px;background-color: lightcyan}#tr01 {text-align: center}</style>
</head>
<body>
<form action="/Cyan_Tomcat/login" methods="get"><table><tr><th colspan="2">User Logging</th></tr><tr><td>Username: </td><td><input type="text" name="username"/></td></tr><tr><td>Password: </td><td><input type="password" name="password"/></td></tr><tr id="tr01"><td><input type="submit" value="Submit"/></td><td><input type="reset" value="Reset"/></td></tr></table>
</form>
</body>
</html>

LoginServlet类代码如下 :

package servlet;import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;/*** @author : Cyan_RA9* @version : 21.0*/
@WebServlet(urlPatterns = {"/login"})
public class LoginServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("LoginServlet's doPost is invoked~");resp.setContentType("text/html; charset=utf-8");PrintWriter writer = resp.getWriter();req.setCharacterEncoding("utf-8");String username = req.getParameter("username");String password = req.getParameter("password");if ("Cyan".equals(username) && "123".equals(password)) {writer.print("<h1>登录成功！</h1>");} else {writer.print("<h1>登录失败！请重新尝试！</h1>");}}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doPost(req, resp);}
}

运行效果 :

如果以Web工程配置好的Tomcat运行，就会按照LoginServlet类的代码逻辑来处理业务，如下图所示 : (GIF)

如果以自定义的Tomcat运行，就会以MyTomcat类中的代码逻辑来处理业务。
如下图所示 : (GIF)

二、多线程模型的实现

1.思路分析 :

当服务器端接收到浏览器端的HTTP请求后，启动一个新的线程，令该线程持有浏览器对应的Socket对象，完成线程和浏览器的对接。
可通过实现Runnable接口的方式定义线程类HttpRequestHandler，线程对象用于处理来自浏览器的HTTP请求。

2.处理HTTP请求 :

线程类HttpRequestHandler类代码如下 :

package tomcat.handler;import tomcat.http.CyanServletRequest;
import tomcat.http.CyanServletResponse;
import tomcat.servlet.CyanLoginServlet;import java.io.*;
import java.net.Socket;public class HttpRequestHandler implements Runnable {private Socket socket;public HttpRequestHandler(Socket socket) {this.socket = socket;}@Overridepublic void run() {try {//接收客户端的信息InputStream inputStream = socket.getInputStream();/*  以下代码已在CyanServletRequest类中实现BufferedReader bufferedReader =new BufferedReader(new InputStreamReader(inputStream, "utf-8"));//BIO，每次请求都对应一个新的线程System.out.println("当前线程 = " + Thread.currentThread().getName());String content = null;  //局部变量在使用前必须赋初值。while ((content = bufferedReader.readLine()) != null) {//判断是否读到了空字符串if (content.length() == 0) {break;}System.out.println(content);}
*///Die first and live second//获取客户端的信息（利用了CyanServletRequest中封装好的方法）//以下代码已在CyanLoginServlet中实现
/*            CyanServletRequest cyanServletRequest = new CyanServletRequest(inputStream);String username = cyanServletRequest.getParameter("username");String password = cyanServletRequest.getParameter("password");System.out.println("username = " + username);System.out.println("password = " + password);System.out.println(cyanServletRequest);*///给客户端回送信息//以下代码已在CyanLoginServlet类中实现。
/*            CyanServletResponse cyanServletResponse = new CyanServletResponse(socket.getOutputStream());String resp = CyanServletResponse.respHeader + "<h1>CyanServletResponse!</h1>";OutputStream outputStream = cyanServletResponse.getOutputStream();outputStream.write(resp.getBytes());outputStream.flush();outputStream.close();*/CyanServletRequest cyanServletRequest = new CyanServletRequest(inputStream);CyanServletResponse cyanServletResponse = new CyanServletResponse(socket.getOutputStream());CyanLoginServlet cyanLoginServlet = new CyanLoginServlet();cyanLoginServlet.doPost(cyanServletRequest, cyanServletResponse);//释放资源inputStream.close();socket.close();/* 以下代码已在CyanServletResponse类中实现 :String respHeader = "HTTP/1.1 200\r\n" +"Content-Type: text/html;charset=utf-8\r\n\r\n";String respHttp = respHeader + "<h1>Cyan_RA9</h1>";System.out.println("-----------------------------------------------");System.out.println("回送的信息如下：(回显)");System.out.println(respHttp);OutputStream outputStream = socket.getOutputStream();outputStream.write(respHttp.getBytes());//释放资源outputStream.flush();outputStream.close();inputStream.close();socket.close(); */} catch (IOException e) {throw new RuntimeException(e);} finally {//确保Socket关闭if (socket != null) {try {socket.close();} catch (IOException e) {throw new RuntimeException(e);}}}}
}

3.自定义Tomcat :

在MyTomcat_EX类中实现线程的分发。
MyTomcat_EX类代码如下 :

package tomcat;import tomcat.handler.HttpRequestHandler;import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;/*** @author : Cyan_RA9* @version : 21.0*/
public class MyTomcat_EX {public static void main(String[] args) throws IOException {ServerSocket serverSocket = new ServerSocket(8080);System.out.println("MyTomcat_EX在8080端口进行监听...");while (!serverSocket.isClosed()) {Socket socket = serverSocket.accept();HttpRequestHandler httpRequestHandler = new HttpRequestHandler(socket);Thread thread = new Thread(httpRequestHandler);thread.start();}}
}

运行效果 : (GIF)

三、自定义Servlet规范

1. HTTP请求和响应 :

1° CyanServletRequest

CyanServletRequest类的作用等同于原始的HttpServletRequest，该类用于封装HTTP请求中的数据，eg : method, URI, 以及表单数据的参数列表等。
CyanServletRequest类代码如下 :

package tomcat.http;import java.io.*;
import java.util.HashMap;/*** @author : Cyan_RA9* @version : 21.0* @function : like the original HttpServletRequest.*/
public class CyanServletRequest {private String method;private String URI;private HashMap<String, String> parametersMapping = new HashMap<>();private InputStream inputStream;/*此处传入的InputStream对象是和Socket关联的InputStream.*/public CyanServletRequest(InputStream inputStream) {this.inputStream = inputStream;//完成对HTTP请求数据的封装this.init();}private void init() {System.out.println("\nCyanServletRequest's init is invoked~");try {//注意转换流的形参列表BufferedReader bufferedReader =new BufferedReader(new InputStreamReader(inputStream, "utf-8"));//首先读取HTTP请求的请求行/* eg :  GET /Cyan/cyan.html HTTP/1.1　*/String requestLine = bufferedReader.readLine();String[] requestLineArr = requestLine.split(" ");//获取methodmethod = requestLineArr[0];//获取URIint index = requestLineArr[1].indexOf("?");if (index == -1) {      //if判断成立，说明请求行中没有参数列表URI = requestLineArr[1];} else {URI = requestLineArr[1].substring(0, index);//获取参数列表String parameters = requestLineArr[1].substring(index + 1);String[] parameterPairs = parameters.split("&");//兼容性处理，防止?后啥都没有。if (null != parameterPairs && !"".equals(parameterPairs)) {for (String parameterPair : parameterPairs) {String[] parameter = parameterPair.split("=");if (parameter.length == 2) { //判断是否为一对完整的"name=value".parametersMapping.put(parameter[0],parameter[1]);}}}}//!!! 直接关闭Socket关联的InputStream，会引起Socket的关闭。//inputStream.close();} catch (UnsupportedEncodingException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}public String getMethod() {return method;}public void setMethod(String method) {this.method = method;}public String getURI() {return URI;}public void setURI(String URI) {this.URI = URI;}//重要public String getParameter(String name) {if (parametersMapping.containsKey(name)) {      //注意此处API的使用！return parametersMapping.get(name);} else {return null;}}@Overridepublic String toString() {return "CyanServletRequest{" +"method='" + method + '\'' +", URI='" + URI + '\'' +", parametersMapping=" + parametersMapping +'}';}
}

CyanServletRequest类测试，运行效果如下GIF :

2° CyanServletResponse

CyanServletResponse类的作用等同于原始的HttpServletResponse，用于封装HTTP响应的相关信息。
CyanServletResponse类代码如下 :

package tomcat.http;import java.io.OutputStream;/*** @author : Cyan_RA9* @version : 21.0* @function : like the original HttpServletResponse*/
public class CyanServletResponse {private OutputStream outputStream;//设置一个HTTP响应头public static final String respHeader = "HTTP/1.1 200\r\n" +"Content-Type: text/html;charset=utf-8\r\n\r\n";//传入与Socket关联的OutputStream对象public CyanServletResponse(OutputStream outputStream) {this.outputStream = outputStream;}public OutputStream getOutputStream() {return outputStream;}
}

运行测试（如下GIF图）：

2.Servlet规范 :

1° CyanServlet

CyanServlet仅保留原生Servlet的init, destroy, service方法，其中，service方法供将来CyanServlet的抽象实现类CyanHttpServlet去重写。注意，service方法的形参列表，要使用自定义的CyanServletRequest 和 CyanServletResponse.
CyanServlet接口，代码如下 :

package tomcat.servlet;import tomcat.http.CyanServletRequest;
import tomcat.http.CyanServletResponse;import java.io.IOException;public interface CyanServlet {void init() throws Exception;void service(CyanServletRequest req, CyanServletResponse resp) throws IOException;void destroy();
}

2° CyanHttpServlet

CyanHttpServlet的作用，类似于原生的HttpServlet；在CyanHttpServlet中实现CyanServlet接口中的service方法，在service方法中，要对HTTP请求的method类型进行判断。

CyanHttpServlet抽象类代码如下 :

package tomcat.servlet;import tomcat.http.CyanServletRequest;
import tomcat.http.CyanServletResponse;import java.io.IOException;public abstract class CyanHttpServlet implements CyanServlet{@Overridepublic void service(CyanServletRequest req, CyanServletResponse resp) throws IOException {//忽略大小写if ("GET".equalsIgnoreCase(req.getMethod())) {this.deGet(req, resp);} else if ("POST".equalsIgnoreCase(req.getMethod())) {this.doPost(req, resp);}}//模板设计模式public abstract void deGet(CyanServletRequest req, CyanServletResponse resp);public abstract void doPost(CyanServletRequest req, CyanServletResponse resp);
}

3° CyanLoginServlet

CyanLoginServlet是一个简单的servlet实例，用于继承CyanHttpServlet抽象类，并实现CyanHttpServlet类中的doGet和doPost抽象方法。之后，在HttpRequestHandler线程类中先尝试直接调用CyanLoginServlet实例。
CyanLoginServlet代码如下 :

package tomcat.servlet;import tomcat.http.CyanServletRequest;
import tomcat.http.CyanServletResponse;import java.io.IOException;
import java.io.OutputStream;public class CyanLoginServlet extends CyanHttpServlet{@Overridepublic void deGet(CyanServletRequest req, CyanServletResponse resp) {doPost(req, resp);}@Overridepublic void doPost(CyanServletRequest req, CyanServletResponse resp) {String username = req.getParameter("username");String password = req.getParameter("password");//获取与当前Socket相关联的OutputStream对象OutputStream outputStream = resp.getOutputStream();String respInfo = CyanServletResponse.respHeader + "<h1>username = " +username + "</h1><br/> " + "<h1>password = " + password + "</h1>" + "<br/>" +"<h3>Cyan_RA9</h3>";try {outputStream.write(respInfo.getBytes());outputStream.flush();outputStream.close();} catch (IOException e) {throw new RuntimeException(e);}}@Overridepublic void init() throws Exception {}@Overridepublic void destroy() {}
}

此外，还需要更新HttpServletHandler类中的类型，将已封装好的代码注释掉，HttpServletHandler类已更新，在上文“多线程模型实现”的HTTP请求处理模块。
运行效果如下图所示 :

3.容器实现 :

1° 思路分析

Tomcat中维护有至少两个大的HashMap容器。以web.xml配置文件的方式为例，其中一个HashMap容器，key存放<url-pattern>，value存放<servlet-name>；另一个HashMap容器，key存放<servlet-name>，value存放通过<servlet-class>来反射生成的servlet实例。

2° web.xml配置文件

web.xml配置文件如下 :

<!DOCTYPE web-app PUBLIC"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN""http://java.sun.com/dtd/web-app_2_3.dtd" ><!--xmlns="http://xmlns.jcp.org/xml/ns/javaee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"version="4.0"-->
<!--IDEA报错——因为这是我们自定义的servlet，IDEA无法识别；无所谓！继续用！-->
<web-app><display-name>Archetype Created Web Application</display-name><servlet><servlet-name>CyanLoginServlet</servlet-name><servlet-class>tomcat.servlet.CyanLoginServlet</servlet-class></servlet><servlet-mapping><servlet-name>CyanLoginServlet</servlet-name><url-pattern>/cyanLogin</url-pattern></servlet-mapping>
</web-app>

3° 最终版自定义Tomcat

在MyTomcat_Pro类中定义两个CurrentHashMap对象；定义init方法完成对两个CurrentHashMap对象的初始化（使用Dom4J读取web.xml配置文件）。
首先，需要在Maven的pom.xml配置文件中，引入dom4j依赖，如下图所示 :

然后，将web.xml配置文件拷贝到/target/classes/目录下一份，如下图所示 :

MyTomcat_Pro代码如下 :

package tomcat;import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import tomcat.handler.HttpRequestHandler;
import tomcat.servlet.CyanHttpServlet;import java.io.File;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;/*** The final own custom Tomcat.*/
public class MyTomcat_Pro {//Tomcat维护的第一个容器//String --> <servlet-name>//CyanHttpServlet --> 可存放它的子类(即各种servlet实例)public static final ConcurrentHashMap<String, CyanHttpServlet> servletMapping =new ConcurrentHashMap<>();//Tomcat维护的第二个容器//String --> <url-patterns>//String --> <servlet-name>public static final ConcurrentHashMap<String, String> servletURLMapping =new ConcurrentHashMap<>();public static void main(String[] args) {MyTomcat_Pro myTomcat_pro = new MyTomcat_Pro();myTomcat_pro.init();myTomcat_pro.run();}public void run() {try {ServerSocket serverSocket = new ServerSocket(8080);System.out.println("MyTomcat_Pro在8080端口进行监听...");while (!serverSocket.isClosed()) {Socket socket = serverSocket.accept();Thread thread = new Thread(new HttpRequestHandler(socket));thread.start();}} catch (IOException e) {throw new RuntimeException(e);}}public void init() {String path = MyTomcat_Pro.class.getResource("/").getPath();//path = "/javaProject/Servlet/Cyan_Tomcat/target/classes/"//使用Dom4J技术解析web.xml文件SAXReader saxReader = new SAXReader();try {//注意文件名Document document = saxReader.read(new File(path + "web.xml"));System.out.println("document = " + document);//获取根元素<web-app>Element rootElement = document.getRootElement();//得到根元素下面的所有子元素List<Element> elements = rootElement.elements();//遍历并判断for (Element element : elements) {if ("servlet".equals(element.getName())) {Element servlet_name = element.element("servlet-name");Element servlet_class = element.element("servlet-class");//反射机制创建servlet实例 (注意getText()方法的使用！)Class<?> clazz = Class.forName(servlet_class.getText().trim());Constructor<?> constructor = clazz.getConstructor();CyanHttpServlet o = (CyanHttpServlet) constructor.newInstance();servletMapping.put(servlet_name.getText(), o);} else if ("servlet-mapping".equals(element.getName())) {Element url_pattern = element.element("url-pattern");Element servlet_name = element.element("servlet-name");servletURLMapping.put(url_pattern.getText(), servlet_name.getText());}}} catch (Exception e) {throw new RuntimeException(e);}}
}

4° 最终版自定义线程类

package tomcat.handler;import tomcat.MyTomcat_Pro;
import tomcat.http.CyanServletRequest;
import tomcat.http.CyanServletResponse;
import tomcat.servlet.CyanHttpServlet;
import tomcat.servlet.CyanLoginServlet;import java.io.*;
import java.net.Socket;public class HttpRequestHandler implements Runnable {private Socket socket;public HttpRequestHandler(Socket socket) {this.socket = socket;}@Overridepublic void run() {try {//接收客户端的信息CyanServletRequest cyanServletRequest = new CyanServletRequest(socket.getInputStream());CyanServletResponse cyanServletResponse = new CyanServletResponse(socket.getOutputStream());String uri = cyanServletRequest.getURI();System.out.println("uri = " + uri);String servlet_name = MyTomcat_Pro.servletURLMapping.get(uri);/*这里的servlet_name可能为空。解决方式一 : 将CurrentHashMap替换为HashMap解决方式二 : 增加一个是否为null的判断。*/if (servlet_name == null) {servlet_name = "";}//多态 --> 动态绑定CyanHttpServlet cyanHttpServlet = MyTomcat_Pro.servletMapping.get(servlet_name);if (cyanHttpServlet != null) {  //判断是否正常得到servlet实例cyanHttpServlet.service(cyanServletRequest, cyanServletResponse);} else {//如果没有找到servlet，返回404String resp = CyanServletResponse.respHeader + "<h1>404 Not Found!</h1>";OutputStream outputStream = cyanServletResponse.getOutputStream();outputStream.write(resp.getBytes());outputStream.flush();outputStream.close();}//释放资源socket.close();} catch (IOException e) {throw new RuntimeException(e);} finally {//确保Socket关闭if (socket != null) {try {socket.close();} catch (IOException e) {throw new RuntimeException(e);}}}}
}