Question

所以我被要求创建一个UDP消息传递应用程序。我有两个客户端在同一台计算机上从命令行运行，我试图让每个客户端在从另一个客户端收到字符串"exit"时突破while循环，因此它们都终止同时进行。

在此代码上方创建了

String input，因此如果此客户端输入"exit"，则跳过while（这很好用！）。

DatagramSocket receiveSocket = new DatagramSocket(8000); //Port 8000
byte[] receiveBuffer = new byte[65508];

while(!input.equals("exit")) {

    DatagramPacket packetToReceive = new DatagramPacket(receiveBuffer, receiveBuffer.length);

    receiveSocket.receive(packetToReceive);
    receiveBuffer = packetToReceive.getData();

    String receivedMessage = new String(receiveBuffer);


    if(!receivedMessage.equals("exit")) {   
        System.out.println("A says: " + receivedMessage);
    }
    else {
        input = "exit";
    }
}

我遇到的问题是我无法将!receivedMessage.equals("exit")等同于false，即使我执行System.out.println(receivedMessage)时，我也会"exit"。它们看起来完全一样，但显然不是。我试过强制编码，比如......

String receivedMessage = new String(receiveBuffer, "UTF-8");

......但没有任何作用。我尝试了许多强制编码的其他组合，并将receivedMessage转换为Byte数组，char数组等进行比较，并且我已检查receivedMessage两侧的空格，仍然没有。

任何帮助将不胜感激。它必须是我想念的小东西。感谢。

Answer 1

也许在receivedMessage中有一些前导或尾随空格。试着修剪它。

Answer 2

receiveBuffer 大小可能存在问题。目前，您正在数据包中发送“退出”，该数据包足够小，可以容纳 65508 字节。因此， receiveBuffer 中的剩余字节只是空的或包含特殊字符。这就是为什么当您收到数据包并将数据转换为字符串时，字符串中的剩余字节也存在。

您可以使用contains()代替equals()来比较字符串，也可以只将包含实际消息的所需字节放入receiveBuffer。以下是实现这一目标的可能方法之一：

receiveSocket.receive(packetToReceive);
receiveBuffer = new byte[packetToReceive.getLength()];
System.arraycopy(packetToReceive.getData(), packetToReceive.getOffset(), receiveBuffer, 0, packetToReceive.getLength());

String receivedMessage = new String(receiveBuffer);

if(!receivedMessage.equals("exit")) {   
    System.out.println("A says: " + receivedMessage);
}
else {
    input = "exit";
}

Answer 3

receiveSocket.receive(packetToReceive);
receiveBuffer = packetToReceive.getData();
String receivedMessage = new String(receiveBuffer);

问题出在这里。你忽略了收到的数据包的长度。最后两行可以改为：

String receivedMessage = new String(packetToReceive.getData(), packetToReceive.getOffset(), packetToReceive.getLength());

比较String和String（来自DatagramPacket的字节数组）

3 个答案: