Java采用Socket技术编写http服务器和http客户端，服务器可以多线程处理客户端请求，以及实现HEAD、POST、GET请求的代码

以下是Java使用Socket技术编写HTTP服务器和客户端的示例代码（包括多线程处理客户端请求，以及实现HEAD、POST、GET请求）：

HTTP服务器代码：

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

public class HttpServer {
    public static void main(String[] args) {
        try {
            ServerSocket ss = new ServerSocket(8080); // 创建服务器套接字
            while (true) { // 循环监听客户端请求
                Socket s = ss.accept(); // 等待客户端连接
                new Thread(new Handler(s)).start(); // 创建线程处理客户端请求
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    static class Handler implements Runnable {
        private Socket socket;

        public Handler(Socket socket) {
            this.socket = socket;
        }

        @Override
        public void run() {
            try {
                BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream())); // 读取客户端请求
                String request = br.readLine();
                String method = request.split("\\s+")[0]; // 获取请求方法
                String url = request.split("\\s+")[1]; // 获取请求URL
                String version = request.split("\\s+")[2]; // 获取HTTP版本号
                System.out.println("Method: " + method);
                System.out.println("URL: " + url);
                System.out.println("Version: " + version);

                while (br.readLine() != null) { // 忽略请求头部
                    if ("".equals(br.readLine())) {
                        break;
                    }
                }

                OutputStream os = socket.getOutputStream(); // 发送响应
                if ("GET".equals(method)) { // 处理GET请求
                    File file = new File(url.substring(1));
                    if (file.exists() && !file.isDirectory()) {
                        FileInputStream fis = new FileInputStream(file);
                        byte[] buffer = new byte[1024];
                        int len;
                        while ((len = fis.read(buffer)) != -1) {
                            os.write(buffer, 0, len);
                        }
                        fis.close();
                    } else {
                        os.write("404 Not Found".getBytes());
                    }
                } else if ("HEAD".equals(method)) { // 处理HEAD请求
                    File file = new File(url.substring(1));
                    if (file.exists() && !file.isDirectory()) {
                        os.write("HTTP/1.1 200 OK\r\n".getBytes());
                        os.write(("Content-Length: " + file.length() + "\r\n").getBytes());
                        os.write("\r\n".getBytes());
                    } else {
                        os.write("404 Not Found".getBytes());
                    }
                } else if ("POST".equals(method)) { // 处理POST请求
                    String line;
                    StringBuilder sb = new StringBuilder();
                    while ((line = br.readLine()) != null) {
                        sb.append(line);
                    }
                    os.write(("HTTP/1.1 200 OK\r\n\r\n" + sb.toString()).getBytes());
                } else {
                    os.write("501 Not Implemented".getBytes());
                }

                os.flush();
                os.close();
                br.close();
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

HTTP客户端代码：

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

public class HttpClient {
    public static void main(String[] args) {
        try {
            Socket s = new Socket("localhost", 8080); // 创建客户端套接字，连接到服务器
            OutputStream os = s.getOutputStream(); // 发送请求
            String request = "GET /index.html HTTP/1.1\r\n" + "Host: localhost:8080\r\n" + "\r\n";
            os.write(request.getBytes());

            BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream())); // 读取响应
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }

            os.close();
            br.close();
            s.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

注意：以上代码仅为示例，实际应用中需要考虑安全性、性能等因素。