Java UDP服务器-客户端显示方形字符

Question

我使用了一个在这里找到的UDP服务器/客户端的示例： http : //systembash.com/content/a-simple-java-udp-server-and-udp-client/

客户端向服务器发送一个字符串，服务器将小写字母更改为大写字母。

服务器：

import java.io.*;
import java.net.*;
class UDPServer
{

public static void main(String args[]) throws Exception
{
    DatagramSocket serverSocket = new DatagramSocket(9876);
    byte[] receiveData = new byte[1024];
    byte[] sendData = new byte[1024];

    while(true) {   
        DatagramPacket receivePacket = new DatagramPacket(receiveData,     receiveData.length);
        serverSocket.receive(receivePacket);

        String sentence = new String( receivePacket.getData());
        System.out.println("RECEIVED: " + sentence);
        InetAddress IPAddress = receivePacket.getAddress();

        int port = receivePacket.getPort();
        String capitalizedSentence = sentence.toUpperCase();
        sendData = capitalizedSentence.getBytes();

        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);
        serverSocket.send(sendPacket);
    }
}

}

客户端：

import java.io.*;
import java.net.*;
class UDPClient
{
public static void main(String args[]) throws Exception
{
    BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in,     "UTF-16"));

    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);

    DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    clientSocket.receive(receivePacket);

    String modifiedSentence = new String(receivePacket.getData());
    System.out.println("FROM SERVER:" + modifiedSentence);
    clientSocket.close();
}
}

我在客户端编写测试时的输出：

test
FROM SERVER:TEST□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□.....

Answer 1

因为您声明了数据包大小：

byte[] receiveData = new byte[1024];
DatagramPacket receivePacket = 
   new DatagramPacket(receiveData, receiveData.length);

以下代码将返回长度为1024的字符串：

String sentence = new String( receivePacket.getData() );

您需要使用receivePacket.getLength（）来获取有效负载大小，因此将其更改为：

String sentence = new String( receivePacket.getData(), 0, receivePacket.getLength() );

那应该做！