How tomcat works（1）一个简单的Web服务器

Http 1.1协议基本内容
Http 请求:
【1】请求方法--统一资源标识符--协议/版本
【2】请求头
【3】CRLF(回车（CR）换行（LF）)
【4】请求实体

样例如下：

POST /index.html  HTTP/1.1
Accept: text/plain; text/html
Connection: keep-Alive
Connect-length: 33
Content-type: application/x-www-form-urlencode

lastName=Franks&firstName=Michael

Http响应:
【1】协议--状态码--描述
【2】响应头
【3】CRLF(空行)
【4】响应实体

样例如下：

HTTP/1.1 200 OK
Content-Type: text/html
Content-length: 112

<html>
  <head>
      <title>Http ResponseExampple</title>
  </head>
<body>
  Welcome to Brainy Software
</body>
</html>

这里的Html片段在实际的响应中是一个将会是一个字节流。

备注：我们的请求/响应都必须是严格按照规范上定义的去构造的，否则将会导致请求无效或者响应无效，因为浏览器就是按照这个标准去包装和解析数据的。下面举例实现一个简单的Http服务器：

简单的Http服务构建

Request.java

package com.ex01;

import java.io.IOException;
import java.io.InputStream;

/**
 * @program: tomcat work
 * @description:
 * @author: ggr
 * @create: 2019-06-14 16:26
 **/
public class Request {

    private InputStream input;
    private String uri;

    public Request(InputStream input) {
        this.input = input;
    }

    public void parse() {
        // Read a set of characters from the socket
        StringBuffer request = new StringBuffer(2048);
        int i;
        byte[] buffer = new byte[2048];
        try {
            i = input.read(buffer);
        } catch (IOException e) {
            e.printStackTrace();
            i = -1;
        }
        for (int j = 0; j < i; j++) {
            request.append((char) buffer[j]);
        }
        System.out.print(request.toString());
        uri = parseUri(request.toString());
    }

    private String parseUri(String requestString) {
        int index1, index2;
        index1 = requestString.indexOf(' ');
        if (index1 != -1) {
            index2 = requestString.indexOf(' ', index1 + 1);
            if (index2 > index1) {
                return requestString.substring(index1 + 1, index2);
            }
        }
        return null;
    }

    public String getUri() {
        return uri;
    }

}

Response.java

package com.ex01;

import java.io.*;

/**
 * @program: tomcat work
 * @description:
 * @author: ggr
 * @create: 2019-06-14 16:29
 **/
public class Response {

    private static final int BUFFER_SIZE = 1024;
    Request request;
    OutputStream output;

    public Response(OutputStream output) {
        this.output = output;
    }

    public void setRequest(Request request) {
        this.request = request;
    }

    /*** 这里将按照上面Response的结构一行一行地构造，如果丢失了正常的结构将会导致
    * 浏览器无法正常解析这个响应，并认为这个一个无效的响应
    */
    public void sendStaticResource() throws IOException {
        byte[] bytes = new byte[BUFFER_SIZE];
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(request.getUri().substring(1));
        try {
            output.write(("HTTP/1.1 200 OK\n" + "Content-Type: text/html; charset=utf-8\r\n").getBytes());
             int available = resourceAsStream.available();
            output.write(("Content-Length: " + available + "\n").getBytes());
                output.write("Connection: close\r\n".getBytes());
                int ch = resourceAsStream.read(bytes, 0, BUFFER_SIZE);
                while (ch != -1) {
                    output.write(bytes, 0, ch);
                    ch = resourceAsStream.read(bytes, 0, BUFFER_SIZE);
                }
        } catch (Exception e) {
            // thrown if cannot instantiate a File object
            System.out.println(e.toString());
        } finally {
            if (resourceAsStream != null) {
                resourceAsStream.close();
            }
        }
    }
}

HttpServer.java

package com.ex01;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * @program: tomcat work
 * @description:
 * @author: ggr
 * @create: 2019-06-14 16:29
 **/
public class HttpServer {

    public static final String WEB_ROOT = "webRoot";

    // shutdown command
    private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";

    private boolean shutdown = false;

    public static void main(String[] args) {
        HttpServer server = new HttpServer();
        server.await();
    }

    public void await() {
        ServerSocket serverSocket = null;
        int port = 8080;
        try {
            serverSocket =  new ServerSocket(port, 1, InetAddress.getByName("127.0.0.1"));
        }
        catch (IOException e) {
            e.printStackTrace();
            System.exit(1);
        }

        // Loop waiting for a request
        while (!shutdown) {
            Socket socket = null;
            InputStream input = null;
            OutputStream output = null;
            try {
                socket = serverSocket.accept();
                input = socket.getInputStream();
                output = socket.getOutputStream();

                // create Request object and parse
                Request request = new Request(input);
                request.parse();

                // create Response object
                Response response = new Response(output);
                response.setRequest(request);
                response.sendStaticResource();

                // Close the socket
                socket.close();

                //check if the previous URI is a shutdown command
                shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
            } catch (Exception e) {
                e.printStackTrace();
                continue;
            }
        }
    }
}