Java服务器停止接收更新并抛出“IOException：servernullerror”的错误。

这个错误通常是由于服务器程序崩溃或关闭引起的，导致客户端无法连接到服务器。为了解决这个问题，可以采取以下措施：

1.查看服务器程序是否有异常或错误导致崩溃或关闭；

2.检查网络连接是否正常，确保服务器可以正常连接到互联网或局域网；

3.检查服务器程序中是否有必要的数据结构或变量为空或未初始化引起的错误；

4.重启服务器程序，并检查日志或输出来查找错误信息。

代码示例：

// 服务器程序示例

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

public class Server { public static void main(String[] args) throws IOException { ServerSocket serverSocket = null;

    try {
        serverSocket = new ServerSocket(8080);
    } catch (IOException e) {
        System.err.println("Could not listen on port: 8080.");
        System.exit(1);
    }

    Socket clientSocket = null;
    try {
        clientSocket = serverSocket.accept();
    } catch (IOException e) {
        System.err.println("Accept failed.");
        System.exit(1);
    }

    PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
    BufferedReader in = new BufferedReader(
        new InputStreamReader(
            clientSocket.getInputStream()));
    String inputLine, outputLine;
    while ((inputLine = in.readLine()) != null) {
        outputLine = "Server: " + inputLine;
        out.println(outputLine);
    }
    out.close();
    in.close();
    clientSocket.close();
    serverSocket.close();
}

}

// 客户端程序示例

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

public class Client { public static void main(String[] args) throws IOException { Socket kkSocket = null; PrintWriter out = null; BufferedReader in = null;

    try {
        kkSocket = new Socket("localhost", 8080);
        out = new PrintWriter(kkSocket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(kkSocket.getInputStream()));
    } catch (UnknownHostException e) {
        System.err.println("Don't know about host: localhost.");
        System.exit(1);
    } catch (IOException e) {
        System.err.println("Couldn't get I/O for the connection to: localhost.");
        System.exit(1);
    }

    BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
    String fromServer;
    String fromUser;

    while ((fromServer = in.readLine()) != null) {
        System.out.println("Server: " + fromServer);
        if (fromServer.equals("Bye."))
            break;

        fromUser = stdIn.readLine();
        if (fromUser != null) {
            System.out.println("Client: " + fromUser);
            out.println(fromUser);
        }
    }

    out.close();
    in.close();
    stdIn.close();
    kkSocket.close();
}

}