我不熟悉JAVA中的套接字。最近，我试图建立一个服务器-客户端程序，客户端可以从服务器端的字典中搜索一个单词，服务器会将该单词的定义返回给客户端。服务器端的代码如下:

public class DictionaryServer {

private static int port;
private static String dicFile;
static Map<String, String> dictionary = new HashMap<String, String>();
int userCounter = 0;

public static void main(String[] args) {

    //check if starting the server in valid format
    if (args.length != 2) {
        System.err.println("Invalid format to start DictionaryServer"); 
        System.err.println("Usage: java DictionaryServer <port number> <the name of dictionary>");
        System.exit(1);
    }


    port = Integer.parseInt(args[0]);
    dicFile = args[1];


    try{
        System.out.println("IP: " + InetAddress.getLocalHost());
        System.out.println("port: " + port);
    }
    catch(UnknownHostException e){
        e.printStackTrace();
    }
    DictionaryServer s = new DictionaryServer();
    s.server(port, dicFile);

}


public void server(int port, String dicFile) {
    ServerSocketFactory serverSocket = ServerSocketFactory.getDefault();

    try(ServerSocket server = serverSocket.createServerSocket(port)){

        System.out.println("Server IP: " + server.getInetAddress());
        System.out.println("Listening for client connections...");

        while(true){
            Socket client = server.accept();
            System.out.println("Client \"" + client.getRemoteSocketAddress().toString()
                    + "\""+ " is connecting.");


            Thread t = new Thread(() -> service(client, dicFile));
            t.start();

        }
    }
    catch (UnknownHostException e) {
        e.printStackTrace();
    }
    catch(IOException e) {
        e.printStackTrace();
    }

}

public void service(Socket client, String dicFile){
    try(Socket clientSocket = client){
        // Input and Output stream of the client
        DataInputStream input = new DataInputStream(
                clientSocket.getInputStream());
        DataOutputStream output = new DataOutputStream(
                clientSocket.getOutputStream());

        //check request
        int action = input.readInt();   //1:add, 2:remove, 3:query
        String word = input.readUTF();

        //choose action
        Dic d = new Dic(dicFile);
        switch(action){
            case 1: //add
                String definition = input.readUTF();
                output.writeUTF(d.add(word, definition, dicFile));
                break;

            case 2: //remove
                output.writeUTF(d.remove(word, dicFile));
                break;

            case 3: //query
                output.writeUTF(d.query(word, dicFile));
                break;
        }
    }
    catch(IOException e){
        String message=e.getMessage();
        System.out.println(message);
        System.out.println();
    }   
}   

当我试图重新启动服务器程序时，遇到了一个错误：java.net.BindException：地址已在使用中（绑定失败）

例如，上次我用端口4000执行服务器程序时，它工作了，但如果我想再次用同一端口执行服务器程序，就会出现异常。我通过码头上的“lsof-I:4000”检查了端口4000正在做什么，它告诉我：

COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
java    19683 Andy    7u  IPv6 0x43e8f876eb74b731      0t0  TCP *:terabase (LISTEN)

有谁知道我该如何解决这个问题？谢谢！