《How Tomcat Works》读书笔记一

1. "《How Tomcat Works_Chapter 1: A Simple Web Server》"
   1.1: HTTP hypetext transfer protocal,
   1.2: Request: split a uri from address input
   1.3: Response: get the uri to read the file from the servers
   1.4: HttpServer: new a socket to receive & send bytes info
2. "《How Tomcat Works_Chapter 2: A Simple Servlet Container》"
   2.1: When the servlet is called for the first time, load the servlet class and call the
        servlet's' init method (once only)
   2.2: For each request, construct an instance of javax.servlet.ServletRequest and
        an instance of javax.servlet.ServletResponse.
   2.3: Invoke the servlet's' service method, passing the ServletRequest and
        ServletResponse objects.
   2.4: When the servlet class is shut down, call the servlet's' destroy method and
        unload the servlet class.

HttpServer.java:

package chap1_ASimpleWebServer;
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;


public class HttpServer {
    public static final String WEB_ROOT = System.getProperty("user.dir") + File.separator + "webroot";

    private static final String SHUTDOWN_COMMAND = "/SHUTDOWN";
    
    private boolean shutdown = false;
    
    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 & parse
                Request request = new Request(input);
                request.parse();
                // create Response object
                Response response = new Response(output);
                response.setRequest(request);
                response.sendResource();
                // close socket
                socket.close();
                // check if the previous URI is a shutdown command
                shutdown = request.getUri().equals(SHUTDOWN_COMMAND);
            } catch (IOException e) {
                e.printStackTrace();
                continue;
            }
        }
    }
    
    public static void main(String[] args) {
        System.out.println(WEB_ROOT);
        HttpServer server = new HttpServer();
        server.await();
    }
}

Request.java:

package chap1_ASimpleWebServer;
import java.io.IOException;
import java.io.InputStream;


public class Request {
    private InputStream input;
    private String uri;
    
    public Request (InputStream input) {
        this.input = input;
    }
    
    public void parse() {
        StringBuffer request = new StringBuffer(2048);
        int len;
        byte[] buffer = new byte[2048];
        try {
            len = input.read(buffer);
        } catch (IOException e) {
            e.printStackTrace();
            len = -1;
        }
        for (int i = 0; i < len; i++) {
            request.append((char)buffer[i]);  // do not forget cast type byte to char
        }
        System.out.println(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 chap1_ASimpleWebServer;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;


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;
    }
    
    public void sendResource() throws IOException {
        byte[] bytes = new byte[BUFFER_SIZE];
        FileInputStream fis = null;
        try {
            File file = new File(HttpServer.WEB_ROOT, request.getUri());
            System.out.println(request.getUri().toString());
            if (file.exists()) {

                fis = new FileInputStream(file);
                int len = fis.read(bytes, 0, BUFFER_SIZE);
                while (len != -1) {
                    output.write(bytes, 0, len);
                    len = fis.read(bytes, 0, BUFFER_SIZE);
                }
            } else {
                String errorMessage = "HTTP/1.1 404 File Not Found\r\n" +
                                      "ContentType: text/html\r\n" +
                                      "ContentLength: 23\r\n\r\n" +
                                      "<head>File Not Found</head>";
                output.write(errorMessage.getBytes());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                fis.close();
            }
        }
    }
}

简单的html, 放在webroot文件夹下：

<html>
    <head>
        <title>Hello Tomcat!</title>
    </head>
    <body>
        <img src="./images/tomcat.jpg">
        <br>
        <h1>It's Works!</h1>.
    </body>
</html>

直接java application 运行， 在页面上即可，结果如下：

光是如此是远远不够的， 所以我们还要增加对java文件的支持（Servlet文件）。。。