【JavaWeb】Tomcat底层机制和Servlet运行原理-阿里云开发者社区

一. 一图明理

二. 概念

Tomcat是一个开源的Java Web服务器，它是基于Java Servlet和JavaServer Pages（JSP）技术的。下面是关于Tomcat底层机制和Servlet运行原理的简要说明：

Tomcat底层机制：

网络通信：Tomcat使用Java的Socket API来监听特定的端口（通常是8080），接收来自客户端的HTTP请求。

线程池：Tomcat使用线程池来处理并发的请求。当有新的请求到达时，Tomcat会从线程池中获取一个空闲线程来处理该请求，这样可以提高处理效率。

生命周期管理：Tomcat负责管理Servlet和其他Web组件的生命周期，包括初始化、请求处理和销毁等阶段。(init(), run())

请求处理管道：Tomcat通过请求处理管道来处理HTTP请求。请求经过一系列的处理器，如身份验证、日志记录和安全检查等，最终被交给适当的Servlet进行处理。(handle())

连接池：Tomcat使用连接池来管理与数据库的连接。这样可以提高性能，并避免频繁地创建和销毁数据库连接。(handle())

Servlet运行原理：

Servlet容器：Tomcat是一个Servlet容器，它负责加载、初始化和管理Servlet。当Tomcat启动时，它会读取配置文件（如web.xml）来确定需要加载的Servlet类。

生命周期：每个Servlet都有自己的生命周期，包括初始化、请求处理和销毁等阶段。Tomcat会在适当的时间调用Servlet的生命周期方法（如init()、service()和destroy()）。

请求处理：当Tomcat接收到HTTP请求时，它会根据请求的URL找到对应的Servlet，并将请求转发给该Servlet进行处理。Servlet通过HttpServletRequest对象获取请求的信息，并通过HttpServletResponse对象发送响应给客户端。

多线程处理：Tomcat使用多线程来处理并发请求。每个请求都被分配给一个独立的线程进行处理，这样可以同时处理多个请求，提高服务器的性能。

三. 容器的理解

在tomcat底层实现中, servlet作为容器, 实现可以理解为HashMap, 键是servlet-name值是servlet-class, 而HashMap就是一个容器, 从容器中得到一个servlet实例, 对其进行初始化, 供web使用, 调用其中的service()方法, service()方法对HTTP请求的method进行判断, 对每个相应的method都有相应的do方法, 可以使用.

四. 案例

不用tomcat以及servlet实现

五. 代码分析和代码实现

LxbRequestHandle类

package com.lxb.tomcat.handle;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 13:22:00
//@Authors : 罗雄波
//@File : LxbRequestHandle.java
//@Software : IntelliJ IDEA
 
import com.lxb.tomcat.LxbTomcatV3;
import com.lxb.tomcat.http.LxbHttpRequest;
import com.lxb.tomcat.http.LxbHttpResponse;
import com.lxb.tomcat.servlet.LxbHttpServlet;
import com.lxb.tomcat.utils.WebUtils;
 
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
 
public class LxbRequestHandle implements Runnable{
    private Socket accept;
 
    public LxbRequestHandle(Socket socket) {
        this.accept = socket;
    }
 
    public void run() {
        try {
            LxbHttpRequest request = new LxbHttpRequest(accept);
            LxbHttpResponse response = new LxbHttpResponse(accept.getOutputStream());
 
            String uri = request.getUri();
            if(WebUtils.isHtml(uri)) {
                System.out.println(uri.substring(1));
                String resp = WebUtils.readFile(uri.substring(1));
                String responseInfo = LxbHttpResponse.respHeader + resp;
 
                OutputStream outputStream = response.getOutputStream();
                outputStream.write(responseInfo.getBytes());
 
                outputStream.flush();
                outputStream.close();
                accept.close();
                return;
            }
 
 
            String servletName = LxbTomcatV3.servletMapping.get(uri);
            if(servletName == null) {
                servletName = "";
            }
 
            LxbHttpServlet servlet = LxbTomcatV3.servlet.get(servletName);
 
            if(servlet != null) {
                servlet.service(request, response);
            } else {
                String resp = LxbHttpResponse.respHeader + "<h1>404 not found!!!</h>";
                OutputStream responseOutputStream = response.getOutputStream();
                responseOutputStream.write(resp.getBytes());
                responseOutputStream.flush();
                responseOutputStream.close();
            }
 
            accept.close();
 
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            if (accept != null) {
                try {
                    accept.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

LxbHttpRequest和LxbHttpResponse

package com.lxb.tomcat.http;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 14:59:24
//@Authors : 罗雄波
//@File : LxbHttpRequest.java
//@Software : IntelliJ IDEA
 
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.Socket;
import java.util.HashMap;
 
public class LxbHttpRequest {
    private Socket socket;
    private String method;
    private String uri;
    private HashMap<String, String> parameterMapping = new HashMap<String, String>();
 
    public LxbHttpRequest(Socket socket) {
        this.socket = socket;
        try {
            ParseProcess();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
 
    public void ParseProcess() throws Exception {
        BufferedReader reader =
                new BufferedReader(new InputStreamReader(socket.getInputStream(), "utf-8"));
 
        String temp;
 
        temp = reader.readLine();
 
//        GET /cal.html HTTP/1.1
        String[] request = temp.split(" ");
        method = request[0];
        int index = request[1].indexOf("?");
 
        if (index == -1) {
            uri = request[1];
        } else {
            uri = request[1].substring(0, index);
 
            String parameterPair = request[1].substring(index + 1);
            String[] parameters = parameterPair.split("&");
 
            if (parameters[0] != null && !parameters[0].equals("")) {
                for (String parameter : parameters) {
                    String[] split = parameter.split("=");
 
                    if(split.length == 2) {
                        parameterMapping.put(split[0], split[1]);
                    }
                }
            }
        }
    }
 
    public String getMethod() {
        return method;
    }
 
    public String getUri() {
        return uri;
    }
 
    public String getParameter(String key) {
        if(parameterMapping.get(key) != null) {
            return parameterMapping.get(key);
        } else {
            return "";
        }
    }
 
    @Override
    public String toString() {
        return "LxbHttpRequest" +
                "{ method = " + method +
                ", uri = " +  uri +
                ", parameter = " + parameterMapping +
                "}";
    }
}

package com.lxb.tomcat.http;

package com.lxb.tomcat.http;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 15:49:29
//@Authors : 罗雄波
//@File : LxbHttpResponse.java
//@Software : IntelliJ IDEA
 
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
 
public class LxbHttpResponse {
    private OutputStream outputStream = null;
    public static final String respHeader = "HTTP/1.1 200 OK\r\n" +
            "Content-Type: text/html;charset=utf-8\r\n\r\n";
    public LxbHttpResponse(OutputStream outputStream) {
        this.outputStream = outputStream;
    }
 
    public OutputStream getOutputStream() {
        return outputStream;
    }
}

LxbTomcat

package com.lxb.tomcat;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 15:37:29
//@Authors : 罗雄波
//@File : LxbTomcatV3.java
//@Software : IntelliJ IDEA
 
import com.lxb.tomcat.handle.LxbRequestHandle;
import com.lxb.tomcat.servlet.LxbHttpServlet;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.junit.Test;
 
import java.io.File;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
 
public class LxbTomcatV3 {
    public static ConcurrentHashMap<String, LxbHttpServlet> servlet =
            new ConcurrentHashMap<String, LxbHttpServlet>();
 
    public static ConcurrentHashMap<String, String> servletMapping =
            new ConcurrentHashMap<String, String>();
 
    public static void main(String[] args) throws Exception {
        LxbTomcatV3 lxbTomcatV3 = new LxbTomcatV3();
        lxbTomcatV3.Init();
        lxbTomcatV3.run();
    }
 
    public void run() {
        try {
            ServerSocket socket = new ServerSocket(8080);
            while (!socket.isClosed()) {
                Socket accept = socket.accept();
 
                LxbRequestHandle requestHandle = new LxbRequestHandle(accept);
 
                new Thread(requestHandle).start();
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
 
    @Test
    public void Init() {
        String path = LxbTomcatV3.class.getResource("/").getPath();
//        System.out.println(path);
//   该类的路径 /D:/NewExecllction/exicese%20code/lxb-tomcat/target/classes/com/lxb/tomcat/
//   根路径    /D:/NewExecllction/exicese%20code/lxb-tomcat/target/classes/
        SAXReader saxReader = new SAXReader();
        try {
            Document document = saxReader.read(new File(path + "web.xml"));
//            System.out.println(document);
 
            Element rootElement = document.getRootElement();
            List<Element> elements = rootElement.elements();
            for (Element element : elements) {
                if ("servlet".equalsIgnoreCase(element.getName())) {
                    Element servletName = element.element("servlet-name");
                    Element servletClass = element.element("servlet-class");
                    servlet.put(servletName.getText(), (LxbHttpServlet) Class.forName(servletClass.getText().trim()).newInstance());
                } else if ("servlet-mapping".equalsIgnoreCase(element.getName())) {
                    Element servletName = element.element("servlet-name");
                    Element servletUrl = element.element("url-pattern");
                    servletMapping.put(servletUrl.getText(), servletName.getText());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
 
        System.out.println(servlet);
        System.out.println(servletMapping);
    }
 
    @Test
    public void test() {
        String path = LxbTomcatV3.class.getResource("/").getPath();
        System.out.println(path + "web.xml");
    }
}

WebUtils

package com.lxb.tomcat.utils;
//-*- code = utf-8 -*-
//@Time : 2023-07-19 16:00:33
//@Authors : 罗雄波
//@File : WebUtils.java
//@Software : IntelliJ IDEA
 
import org.junit.Test;
 
import java.io.*;
 
public class WebUtils {
    public static int parseInt(String strNum, int defaultVal) {
        try {
            return Integer.parseInt(strNum);
        } catch (NumberFormatException e) {
            System.out.println(strNum + "数字格式异常, 无法包装");
        }
        return defaultVal;
    }
 
    public static boolean isHtml(String uri) {
        return uri.endsWith(".html");
    }
 
    public static String readFile(String filename) {
        String path = com.lxb.tomcat.utils.WebUtils.class.getResource("/").getPath();
        StringBuilder stringBuffer = new StringBuilder();
 
        try {
            System.out.println(path + filename);
            BufferedReader bufferedReader = new BufferedReader(new FileReader(path + filename));
            String buffer = null;
            while ((buffer = bufferedReader.readLine()) != null && !buffer.equals("")) {
                stringBuffer.append(buffer);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return stringBuffer.toString();
    }
}

LxbCalServlet

package com.lxb.tomcat.servlet;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 16:14:24
//@Authors : 罗雄波
//@File : LxbCalServlet.java
//@Software : IntelliJ IDEA
 
import com.lxb.tomcat.http.LxbHttpRequest;
import com.lxb.tomcat.http.LxbHttpResponse;
import com.lxb.tomcat.utils.WebUtils;
 
import java.io.IOException;
import java.io.OutputStream;
 
public class LxbCalServlet extends LxbHttpServlet {
    @Override
    public void doGet(LxbHttpRequest request, LxbHttpResponse response) {
        doPost(request, response);
    }
 
    @Override
    public void doPost(LxbHttpRequest request, LxbHttpResponse response) {
        int num1 = WebUtils.parseInt(request.getParameter("num1"), 0);
        int num2 = WebUtils.parseInt(request.getParameter("num2"), 0);
 
        int result = num1 + num2;
 
        OutputStream outputStream = response.getOutputStream();
 
        String resp = LxbHttpResponse.respHeader + "<h1>求和: " + num1 + "+" + num2 + " = " + result + "</h>";
 
        try {
            outputStream.write(resp.getBytes());
            outputStream.flush();
            outputStream.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
 
    public void init() throws Exception {
 
    }
 
    public void destroy() {
 
    }
}

LxbServlet

package com.lxb.tomcat.servlet;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 16:09:43
//@Authors : 罗雄波
//@File : LxbServlet.java
//@Software : IntelliJ IDEA
 
import com.lxb.tomcat.http.LxbHttpRequest;
import com.lxb.tomcat.http.LxbHttpResponse;
 
import java.io.IOException;
 
public interface LxbServlet {
    void init() throws Exception;
 
    void service(LxbHttpRequest request, LxbHttpResponse response) throws IOException;
 
    void destroy();
}

LxbHttpServlet

package com.lxb.tomcat.servlet;
//-*- code = utf-8 -*-
//@Time : 2023-07-20 16:11:02
//@Authors : 罗雄波
//@File : lxbHttpServlet.java
//@Software : IntelliJ IDEA
 
import com.lxb.tomcat.http.LxbHttpRequest;
import com.lxb.tomcat.http.LxbHttpResponse;
 
import java.io.IOException;
 
public abstract class LxbHttpServlet implements LxbServlet{
    public void service(LxbHttpRequest request, LxbHttpResponse response) throws IOException {
        if(request.getMethod().equals("GET")) {
            this.doGet(request, response);
        } else if(request.getMethod().equals("POST")) {
            this.doPost(request, response);
        }
    }
 
    public void doGet(LxbHttpRequest request, LxbHttpResponse response) {
 
    }
    public void doPost(LxbHttpRequest request, LxbHttpResponse response) {
 
    }
}

六. 注意