如何从服务器端的 LISTEN 状态释放端口

Question

我是 JAVA 中的套接字新手。最近，我正在尝试构建一个服务器-客户端程序，客户端可以从服务器端的字典中搜索单词，服务器将 return 单词的定义发送给客户端。服务器端代码如下：

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();
    }   
}

当我尝试重新启动服务器程序时遇到错误：java.net.BindException：地址已在使用中（绑定失败）

比如我上次用4000端口执行服务器程序是成功的，但是如果我再用同样的端口执行服务器程序，就会出现异常。我在终端中通过 "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！

Answer 1

你需要确定你的程序真的退出了，你还需要设置reuseAddress。为此，您必须在不绑定的情况下创建服务器套接字，设置选项，然后通过三个不同的步骤绑定它：

ServerSocket server = serverSocketFactory.createServerSocket();
server.setReuseAddress(true);
server.bind(new InetSocketAddress(port));

如何从服务器端的 LISTEN 状态释放端口

How to release a port from the state LISTEN at the server side

java

sockets

exception

serversocket

server