public class SimpleHTTPServer1 {
    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(8080);     <===== ❶
        while (true) {     <===== ❷
            Socket client = server.accept();
            try (BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
                 PrintWriter out = new PrintWriter(client.getOutputStream())) {
 
                int oneInt = -1;
                while(-1 != (oneInt = in.read())){
                    System.out.print((char)oneInt);     <===== ❸
                }
 
                String response = "HTTP/1.1 200 OKnnHello, World!";
                out.print(response);
                out.flush();
            }
            client.close();
        }
    }
}

GET /?name=openmaru&age=10 HTTP/1.1     <===== ❶
Host: 127.0.0.1:8080
Connection: keep-alive
Cache-Control: no-cache
User-Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate, br
Accept-Language: ko-KR,ko;q=0.9,en-US;q=0.8,en;q=0.7

POST / HTTP/1.1     <===== ❶
Host: 127.0.0.1:8080
Connection: keep-alive
Content-Length: 20
Cache-Control: no-cache
Content-Type: application/x-www-form-urlencoded     <===== ❷
User-Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate, br
Accept-Language: ko-KR,ko;q=0.9,en-US;q=0.8,en;q=0.7
 
name=openmaru&age=10     <===== ❸

public class SimpleHTTPServer2 {
... 생략 ...
                Map headers = new HashMap<>();
 
                String line;
                while (!(line = in.readLine()).equals("")) {     <===== ❶
                    System.out.println(line);
                    setHeaders(headers, line);
                }
                if ("application/x-www-form-urlencoded".equals(headers.get("Content-Type"))) {     <===== ❷ String messageBody = getMessageBody(in, headers); System.out.println("Request Message Body ====================>");
                    System.out.println(messageBody);
                    System.out.println("====================");
                }
 
                out.println("HTTP/1.1 200 OK");                           <===== ❹
                out.println("Content-Type: text/html;charset=UTF-8");     <===== ❺
                out.println();                                            <===== ❻
                out.println("Hello, World!");                             <===== ❼
                out.flush();                                              <===== ❽
            }
            client.close();
        }
    }
 
 
    private static void setHeaders(Map headers, String line) {     <===== ❾
        String[] parts = line.split(": ");
        if (parts.length == 2) {
            headers.put(parts[0], parts[1]);
        }
    }
 
    private static String getMessageBody(BufferedReader in, Map headers) throws IOException {
        int contentLength = Integer.parseInt(headers.get("Content-Length"));     <===== ❸
        char[] body = new char[contentLength];
        in.read(body, 0, contentLength);
        String messageBody = new String(body);
 
        return messageBody;
    }
}