Question

嗨我有一个udp客户端服务器代码无法正常工作我问一般问题“Shane是个好孩子”两个代码都没有出现错误但是当我运行代码时输出 DatagramPacket sendPacket = new DatagramPacket（sendData，sendData.length，IPAddress，9876）; 而不是让客户端问候服务器。流程应该是服务器初始化并等待客户端 - 客户端问候服务器 - 服务器询问问题 - 客户端响应问题 - 服务器符合是否投票并显示天气或不是人像=。任何有关如何将代码四舍五入的建议都会受到欢迎听到的是服务器代码

import java.net.*;

public class VotingServer {
//private static final int yes = 0;
private static int yes2;

public static void main(String[] args, int getrep) throws Exception{
    // part 1: initialization
    DatagramSocket serverSocket = new DatagramSocket(9876);
    byte[] receiveData = new byte[1024];
    byte[] sendData = new byte[1024];
    InetAddress[] IPAddressList = new InetAddress[5];
    int[] portList = new int[5];

    // part 2: receive the greeting from clients
    for (int i=0; i<1; i++) {
        DatagramPacket receivePacket = 
            new DatagramPacket(receiveData, receiveData.length);
        serverSocket.receive(receivePacket);
        String greeting = new String(receivePacket.getData());
        System.out.println("From Client: " + greeting);

        IPAddressList[i] = receivePacket.getAddress();
        portList[i] = receivePacket.getPort();
    } // for (i)

    // part 3: broadcast the votiong question to all clients
    String question = "is shane a good kid 1 for yes 0 no?\n";
    for (int i=0; i<5; i++) { 
        sendData = question.getBytes();
        DatagramPacket sendPacket = 
            new DatagramPacket(sendData, sendData.length);
        serverSocket.send(sendPacket);

    // part 5: receive the age of client (B)
        DatagramPacket receivePacket = 
            new DatagramPacket(receiveData, receiveData.length);
        serverSocket.receive(receivePacket);
        String ageStr = new String(receivePacket.getData());
        yes2 = Integer.parseInt(ageStr);

        IPAddressList[i] = receivePacket.getAddress();
        portList[i] = receivePacket.getPort();

    // part 6: compute the price (C)
    double count= 0; 
    double no = 0;

    if (yes2 >= 1 ) count = 1;
    else 
        if (yes2 <= 0 ) no = 1;

    // part 7: send the price to client
    String rep = null;
    String countStr = ""+count+"\n";
    String noStr = ""+no+"\n";
    if (no < count) rep = "Is a good kid";
    else 
        if (no > count) rep = "is a bad kid";
    System.out.println(" "+getrep);
    sendData = countStr.getBytes();
    sendData = noStr.getBytes();
    sendData = rep.getBytes();
    DatagramPacket sendPacket1 = 
        new DatagramPacket(sendData, sendData.length);
    serverSocket.send(sendPacket1);

} // main()

}} // UDPServer

这是客户端代码 import java.io. ; import java.net。;

public class ClientVoting {

    public static void main(String[] args) throws Exception {
        // part 1: initialization
        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress IPAddress = InetAddress.getByName("localhost");
        byte[] sendData = new byte[1024];
        byte[] receiveData = new byte[1024];



        String sentence = inFromUser.readLine();
        sendData = sentence.getBytes();
        DatagramPacket sendPacket = 
            new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
        clientSocket.send(sendPacket);


        // part 2: receive the question from server
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        clientSocket.receive(receivePacket);
        String question = new String(receivePacket.getData());
        System.out.println("From Server:" + question);

        String yes2 = inFromUser.readLine();
        sendData = yes2.getBytes();
        DatagramPacket sendPacket1 = 
            new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
        clientSocket.send(sendPacket1);


        // part 4: get the price from server
        receivePacket = new DatagramPacket(receiveData, receiveData.length);
        clientSocket.receive(receivePacket);
        String rep = new String(receivePacket.getData());
        System.out.println("the answer is " + rep);

        // part 4: close the socket
        clientSocket.close();

    } // main()

    } // class UDPClient

谢谢SPF

Answer 1

我在服务器端运行代码时出现NullPointException ...代码本身存在一些问题。第一个是您尝试保留客户端连接实例的Array的索引。此时，你只有一个......

for (int i=0; i<1; i++) {
    DatagramPacket receivePacket = 
        new DatagramPacket(receiveData, receiveData.length);
    serverSocket.receive(receivePacket);
    String greeting = new String(receivePacket.getData());
    System.out.println("From Client: " + greeting);

    IPAddressList[i] = receivePacket.getAddress();
    portList[i] = receivePacket.getPort();
} // for (i)

但是，此时，当您尝试迭代5次时，您的代码很容易出现NullPointException ...

String question = "is shane a good kid 1 for yes 0 no?\n";
for (int i=0; i<5; i++) { 
    sendData = question.getBytes();
    DatagramPacket sendPacket = 
        new DatagramPacket(sendData, sendData.length);
    serverSocket.send(sendPacket);   <<<<---- NPE prone code line...

这是运行代码的结果......

From Client: hello
Exception in thread "main" java.lang.NullPointerException: null buffer || null address
    at java.net.PlainDatagramSocketImpl.send(Native Method)
    at java.net.DatagramSocket.send(DatagramSocket.java:629)
    at com.vasoftware.sf.common.VotingServer.main(VotingServer.java:38)

看看这个异常，我注意到由于你的缓冲区不是null，你的地址就是问题，因为你创建了一个没有客户端连接的IP和端口号的新DatagramPacket ......你必须通过它们到DatagramPacket实例，以便服务器知道谁是尝试通信的客户端...一个非常简单/基本的例子，你想要实现的是http://systembash.com/content/a-simple-java-udp-server-and-udp-client/。下面是我最初的代码修复...你的答案仍然需要缓冲区的一些工作，我将把它留作练习......

这是Server的一个固定代码，它只接受一个客户端...我将把多线程的东西+数据处理程序作为练习...

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.util.Arrays;

public class VotingServer {

  //private static final int yes = 0;
    private static int yes2;

    public static void main(String[] args) throws Exception {
        // part 1: initialization
        DatagramSocket serverSocket = new DatagramSocket(9876);
        byte[] receiveData = new byte[1024];
        byte[] sendData = new byte[1024];
        InetAddress IPAddressList;
        int portList = -1;

        // part 2: receive the greeting from clients
        System.out.println("Ready to receive connections at port " + serverSocket.getLocalPort());
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        serverSocket.receive(receivePacket);
        String greeting = new String(receivePacket.getData());
        System.out.println("From Client: " + greeting);

        IPAddressList = receivePacket.getAddress();
        portList= receivePacket.getPort();

        // part 3: broadcast the votiong question to all clients
        String question = "is shane a good kid 1 for yes 0 no?\n";
        sendData = question.getBytes();
        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddressList, portList);
        serverSocket.send(sendPacket);

    // part 5: receive the age of client (B)
        receiveData = new byte[1024];
        receivePacket = new DatagramPacket(receiveData, receiveData.length);
        serverSocket.receive(receivePacket);
        String ageStr = new String(receivePacket.getData());

        try {
            yes2 = Integer.parseInt(ageStr);   //<<<----- WILL NEVER GET THE VALUE... LEAVING IT AS AN EXERCISE....

        } catch (NumberFormatException nfe) {
            yes2 = 0;
        }

        receivePacket.getAddress();
        receivePacket.getPort();

        // part 6: compute the price (C)
        double count= 0; 
        double no = 0;

        if (yes2 >= 1 ) count = 1;
        else 
            if (yes2 <= 0 ) no = 1;

        // part 7: send the price to client
        // ALSO FIXING SOME CODE HERE AS WELL....
        String rep = null;
        rep = no < count ? "Is a good kid" : "is a bad kid";
        rep += " Server Count: " + count;

        sendData = rep.getBytes();
        DatagramPacket sendPacket1 = new DatagramPacket(sendData, sendData.length, IPAddressList, portList);
        serverSocket.send(sendPacket1);
    }
}

这是客户端：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class ClientVoting {

    public static void main(String[] args) throws Exception {
        // part 1: initialization
        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress IPAddress = InetAddress.getByName("localhost");
        byte[] sendData = new byte[1024];
        byte[] receiveData = new byte[1024];

        System.out.print("What's the question? ");
        String sentence = inFromUser.readLine();
        sendData = sentence.getBytes();
        System.out.println("Attempting to connect the server at port " + 9876);
        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
        clientSocket.send(sendPacket);

        System.out.println("Initial greeting sent... Waiting for response...");

        // part 2: receive the question from server
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
        clientSocket.receive(receivePacket);
        String question = new String(receivePacket.getData());
        System.out.println("From Server:" + question);

        String yes2 = inFromUser.readLine();
        sendData = yes2.getBytes();
        DatagramPacket sendPacket1 = 
            new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
        clientSocket.send(sendPacket1);


        // part 4: get the price from server
        receiveData = new byte[1024];
        receivePacket = new DatagramPacket(receiveData, receiveData.length);
        clientSocket.receive(receivePacket);
        String rep = new String(receivePacket.getData());
        System.out.println("the answer is " + rep);

        // part 4: close the socket
        clientSocket.close();

    } // main()
}

您必须首先执行服务器，因为它将侦听在端口9876上打开的套接字。然后，您可以使用客户端连接到服务器。

###### Here's the output in the server-side... Just added a few details of what's going on...
Ready to receive connections at port 9876
From Client: Marcello

####### Here's the output of the client:
What's the question? Marcello
Attempting to connect the server at port 9876
Initial greeting sent... Waiting for response...
From Server:is shane a good kid 1 for yes 0 no?
the answer is is a bad kid Server Count: 0.0

由于您的要求似乎是设计一个可以处理多个客户端并依靠投票数量的服务器，我还建议您使用不同的线程来处理每个服务器的多线程版本客户端在它自己的线程中并更新静态计数器的值（一个例子是while（true）循环，在这里执行一个带有Executor的新Runnable http://java-x.blogspot.com/2006/11/java-5-executors-threadpool.html）。考虑如所描述的那样创建一个Runnable实例，并将服务器的代码放在public void run（）{}方法实现中......我将把它作为练习留给你...

客户端服务器udp套接字

1 个答案: