尝试用TDP编程套接字，在http客户端中有一些错误，我找不到，当我运行它时会带来错误。

package tcp.client;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;

import edu.uoc.dpcs.lsim.logger.LoggerManager.Level;
import lsim.library.api.LSimLogger;

public class HTTPclient {

    public HTTPclient() {
    }
            
    public String head(String http_server_address, int http_server_port){
        LSimLogger.log(Level.INFO, "start HTTPclient.head ");
        LSimLogger.log(Level.INFO, "HTTP server_address: " + http_server_address);
        LSimLogger.log(Level.INFO, "HTTP server_port: "    + http_server_port);

        /* Complete code  */
        
        String peticio = "HEAD /xai/xai.html HTTP/1.1\r\nAccept\r\n";

        LSimLogger.log(Level.INFO, peticio);

        String resposta = "";
        Socket socket;
        try {
            socket = new Socket(http_server_address, http_server_port);
            LSimLogger.log(Level.INFO, "Socket created");
            OutputStream output = socket.getOutputStream();
            PrintWriter writer = new PrintWriter(output, true);
            writer.println(peticio);
            LSimLogger.log(Level.INFO, "Request sent");

            BufferedReader inputFromServer = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String linia ;
            while ((linia = inputFromServer.readLine()) != null) {
                resposta += linia + "\r\n";
                LSimLogger.log(Level.TRACE, linia);
            }
            
            socket.close();

            LSimLogger.log(Level.INFO, "Response: " + resposta);
        } catch (SocketException e) {
            LSimLogger.log(Level.FATAL, e.getMessage());
            e.printStackTrace();
        } catch (UnknownHostException e) {
            LSimLogger.log(Level.FATAL, e.getMessage());
            e.printStackTrace();
        } catch (IOException e) {
            LSimLogger.log(Level.FATAL, e.getMessage());
            e.printStackTrace();
        }
        
        return resposta;
    }
}

代码已经完成了，根据测试问题，我只需要在字符串peticio的地方编写代码。
错误消息。
HTTP/1.1 400错误请求
有什么帮助吗？