Webserver

WebServer.java

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.*;

public class WebServer {
    public static int PORT = 8080;

    public static Map<String, Long> accesses;

    public static void main(String[] args) {
        try (ServerSocket server = new ServerSocket(PORT)) {
            System.out.println("Server started on port " + PORT);

            accesses = new HashMap<>();

            while (true) {
                Socket socket = server.accept();
                new Thread(() ->
                {
                    try (

                            Writer w = new OutputStreamWriter(socket.getOutputStream());
                            DataOutputStream dw = new DataOutputStream(socket.getOutputStream());
                            BufferedWriter bw = new BufferedWriter(w);

                            Reader r = new InputStreamReader(socket.getInputStream());
                            BufferedReader br = new BufferedReader(r)
                    ) {
                        System.out.println("Connection established on port " + socket.getPort());

                        String line = br.readLine();
                        if (!isValidRequest(line)) {
                            System.out.println("Invalid Request from port " + socket.getPort());
                            System.out.println("Connection closed on port " + socket.getPort());
                            sendHeader(500, bw);
                            return;
                        }

                        String path = line.substring(4, line.lastIndexOf("HTTP") - 1);
                        System.out.println("Request for " + path + " from port " + socket.getPort());

                        if (path.startsWith("/static")) {
                            switch (path.substring(path.lastIndexOf(".") + 1)) {
                                case "html":
                                    sendHeader(200, bw);
                                    try (BufferedReader in = Files.newBufferedReader(
                                            Paths.get(path.replace("/static", "resources")),
                                            StandardCharsets.UTF_8)
                                    ) {
                                        String readLine;
                                        StringBuilder text = new StringBuilder();
                                        while ((readLine = in.readLine()) != null) {
                                            text.append(readLine);
                                        }
                                        sendMessage(text.toString(), bw);
                                    }
                                    break;
                                case "png":
                                    sendHeader(200, bw, "image/png");
                                    try (InputStream in = Files.newInputStream(
                                            Paths.get(path.replace("/static", "resources")))
                                    ) {
                                        sendRawMessage(in.readAllBytes(), dw);
                                    }
                                    break;
                                case "jpg":
                                case "jpeg":
                                    sendHeader(200, bw, "image/jpeg");
                                    try (InputStream in = Files.newInputStream(
                                            Paths.get(path.replace("/static", "resources")))
                                    ) {
                                        sendRawMessage(in.readAllBytes(), dw);
                                    }
                                    break;
                            }
                        } else {
                            switch (path) {
                                case "/":
                                    sendHeader(303, bw, "index.html");
                                    break;
                                case "/index.html":
                                    sendHeader(200, bw);
                                    sendMessage("<h1>Main Page, boring</h1>\n" +
                                            "<a href=\"counter\">Counter</a><br>\n" +
                                            "<a href=\"time\">Time</a><br>\n" +
                                            "<img src=\"/static/image.png\"", bw);
                                    break;
                                case "/time":
                                    sendHeader(200, bw);
                                    sendMessage("<h1>It's " + new Date(System.currentTimeMillis()) + "</h1>", bw);
                                    break;
                                case "/counter":
                                    sendHeader(200, bw);
                                    StringBuilder accessesHTML = new StringBuilder();
                                    for (String key : accesses.keySet()) {
                                        accessesHTML
                                                .append("<tr style=\"background-color: #dddddd\">" + "<th>")
                                                .append(key)
                                                .append("</th>").append("<th>")
                                                .append(accesses.get(key))
                                                .append("</th>")
                                                .append("</tr>");
                                    }
                                    sendMessage("<h1>Counter</h1>" +
                                            "<table>" +
                                            "<tr style=\"background-color: #aaaaaa\">" +
                                            "<th>Website</th>" +
                                            "<th>Accesses</th>" +
                                            "</tr>" +
                                            accessesHTML +
                                            "</table>", bw);
                                    break;
                                default:
                                    sendHeader(404, bw);
                                    sendMessage("<h1>404</h1>\n"
                                            + "<p>\"<b>" + path + "</b>\" wasn't found in our vast databases</p>\n", bw);
                            }
                        }

                        if (accesses.containsKey(path)) {
                            accesses.put(path, accesses.get(path) + 1);
                        } else {
                            accesses.put(path, 0L);
                        }

                        bw.flush();

                        System.out.println("Connection closed on port " + socket.getPort());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }).start();
            }
        } catch (
                IOException e) {
            e.printStackTrace();
        }

    }

    private static boolean isValidRequest(String line) {
        return line.matches("GET [/\\p{L} \\d.]*? HTTP/\\d\\.?\\d?");
    }

    private synchronized static void sendMessage(String message, BufferedWriter bw) throws IOException {
        bw.write("<html>\n" +
                "<header>\n" +
                "<title>SEW</title>\n" +
                "</header>\n" +
                "<body>\n" +
                message +
                "</body>\n" +
                "</html>");
        bw.flush();
    }

    private synchronized static void sendRawMessage(byte[] message, DataOutputStream dw) throws IOException {
        dw.write(message);
        dw.flush();
    }

    private synchronized static void sendHeader(int code, BufferedWriter bw) throws IOException {
        switch (code) {
            case 200:
                bw.write("HTTP/1.1 200 OK\n"
                        + "Connection: close\n"
                        + "Content-Type: text/html\n\n");
                break;
            case 404:
                bw.write("HTTP/1.1 404 NOT FOUND\n"
                        + "Connection: close\n"
                        + "Content-Type: text/html\n\n");
                break;
            case 303:
                bw.write("HTTP/1.1 303 See Other\n"
                        + "Location: /\n");
                break;
            case 500:
                bw.write("HTTP/1.1 500 Internal Server Error\n");
                break;
            default:
                System.err.println("Unknown Response Code: " + code);
        }
    }

    private synchronized static void sendHeader(int code, BufferedWriter bw, String advancedResponseContent) throws IOException {
        switch (code) {
            case 200:
                bw.write("HTTP/1.1 200 OK\n"
                        + "Connection: close\n"
                        + "Content-Type: " + advancedResponseContent + "\n\n");
                break;
            case 404:
                bw.write("HTTP/1.1 404 NOT FOUND\n"
                        + "Connection: close\n"
                        + "Content-Type: " + advancedResponseContent + "\n\n");
                break;
            case 303:
                bw.write("HTTP/1.1 303 See Other\n"
                        + "Location: /" + advancedResponseContent + "\n");
                break;
            default:
                System.err.println("Unknown Response Code");
        }
        bw.flush();
    }
}