完整伺服器原始碼

import java.io.*;
import java.net.*;

class SimpleWebServer {
    public static void main(String[] args) {
        ServerSocket server = null;
        int connections = 0;
        try {
            server = new ServerSocket(80, 5);
            while (connections < 5) {
                Socket client = server.accept();
                serviceClient(client);
                connections++;
            }
        } catch (IOException e) {
            System.err.println("伺服器錯誤: " + e);
        } finally {
            closeQuietly(server);
        }
    }

    static void serviceClient(Socket client) throws IOException {
        DataInputStream in = null;
        DataOutputStream out = null;
        try {
            in = new DataInputStream(client.getInputStream());
            out = new DataOutputStream(client.getOutputStream());

            // 讀取請求頭直到空行
            String line;
            while ((line = in.readLine()) != null) {
                if (line.isEmpty()) {
                    out.writeBytes(buildResponse());
                    break;
                }
            }
        } finally {
            closeQuietly(out);
            closeQuietly(in);
            closeQuietly(client);
        }
    }

    static String buildResponse() {
        return "HTTP/1.0 200 OK\r\n" +
               "Content-Type: text/html; charset=UTF-8\r\n" +
               "Content-Length: 42\r\n" +
               "\r\n" +
               "
Hello from Java!
";
    }

    static void closeQuietly(Closeable c) {
        if (c != null) try { c.close(); } catch (IOException ignored) {}
    }
}

關鍵實作細節

• 連線計數器：示範處理固定數量請求後關閉
• 請求頭解析：讀取至空行即為請求結束
• HTTP 回應格式：狀態行 + 標頭 + 空行 + 實體
• 資源清理：closeQuietly 避免 finally 區塊異常吞沒

HTTP 回應建構最佳實務

StringBuilder resp = new StringBuilder();
resp.append("HTTP/1.1 200 OK\r\n");
resp.append("Server: SimpleJava/1.0\r\n");
resp.append("Date: ").append(new Date()).append("\r\n");
resp.append("Content-Type: text/html; charset=UTF-8\r\n");
resp.append("Content-Length: ").append(body.length).append("\r\n");
resp.append("Connection: close\r\n");
resp.append("\r\n");
resp.append(body);

擴充方向

• 解析請求方法、路徑、查詢字串
• 靜態檔案服務與 MIME 類型對應
• 目錄列表、索引檔案預設
• 支援 HEAD、POST 方法
• 存取日誌與錯誤頁面