您好我使用数据报制作了一个echo客户端 - 服务器代码。代码正在运行,客户端发送的消息正在服务器端接收,然后它们被回送给客户端。以下方案显示了我遇到的问题
1->客户端:嗨,服务器:嗨, 回应:嗨
2->客户端:你好,服务器:你好, 回应:你好 现在,当客户端键入比最后一个短的消息时,会发生以下事情
3->客户:K,服务器:Kello, 回应:K
我无法理解为什么服务器会打印上一条消息的其余字符,这是服务器端代码:
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import javax.swing.SwingUtilities;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollBar;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
public class Server extends JFrame {
int port;
// JTextField textField;
JButton resendPacket;
JTextArea chatWindow;
DatagramSocket socket;
private final int PACKET_SIZE = 124;
private final int port_Number = 6789;
DatagramPacket packet = new DatagramPacket(new byte[PACKET_SIZE], PACKET_SIZE);
InetAddress host;
public Server() {
super("INSTANT ECHO - SERVER");
resendPacket = new JButton("Echo");
chatWindow = new JTextArea();
// add(resendPacket, BorderLayout.SOUTH);
add(new JScrollPane(chatWindow));
setSize(300, 300);
setVisible(true);
}
public void startRunning() {
try {
port = 6777;
socket = new DatagramSocket(port);
showMessage("Server is Ready... \n");
/*resendPacket.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent arg0) {
// TODO Auto-generated method stub
try {
socket.send(packet);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}); */
while(true)
{
processPacket();
}
} catch (SocketException e) {
// TODO: handle exception
showMessage("\n Could not send packet!\n");
e.printStackTrace();
}
}
private void processPacket() {
// create a packet
// receive a packet
try {
socket.receive(packet);
} catch (IOException e) {
// TODO Auto-generated catch block
showMessage("\nCould not receive Packet");
e.printStackTrace();
}
try {
socket.send(packet);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// display the contents of the packet
showMessage(new String(packet.getData()));
// send the packet again to the sender
}
public void showMessage(final String text) {
SwingUtilities.invokeLater(
new Runnable() {
public void run() {
chatWindow.append("\n Packet Data : " + text);
}
});
}
}
这是客户端代码
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Client extends JFrame {
int port = 6777;
JTextField textField;
String data = "hello" ;
// JButton sendPacket;
JTextArea chatWindow;
DatagramSocket socket;
DatagramPacket packet;
private final int PACKET_SIZE = 124;
InetAddress host;
public Client() {
super("INSTANT ECHO - CLIENT");
textField = new JTextField();
try {
host = InetAddress.getByName("127.0.0.1");
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
showMessage("\n Could not find local host");
e.printStackTrace();
}
尝试{
socket = new DatagramSocket();
} catch (SocketException e) {
// TODO Auto-generated catch block
showMessage("\n Could not find Socket");
e.printStackTrace();
}
// textField.setEditable(false);
textField.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent event) {
// TODO Auto-generated method stub
data = event.getActionCommand();
showMessage(event.getActionCommand());
startRunning();
textField.setText("");
}
});
chatWindow = new JTextArea();
add(textField, BorderLayout.SOUTH);
add(new JScrollPane(chatWindow));
setSize(300, 300);
setVisible(true);
}
public void startRunning() {
byte[] bytes_to_send = data.getBytes();
DatagramPacket packet = new DatagramPacket(bytes_to_send,
bytes_to_send.length, host, port);
try {
sendPacket(packet);
setTime();
receivePacket(packet);
socket.receive(packet);
showMessage("\n" + new String(packet.getData()));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
//closeCrap();
}
}
private void sendPacket(DatagramPacket packet) {
try {
textField.setEditable(true);
socket.send(packet);
} catch (IOException e) {
// TODO Auto-generated catch block
showMessage("\nUnable to send Packet !");
e.printStackTrace();
}
}
private void setTime() {
try {
socket.setSoTimeout(5);
} catch (SocketException e) {
// TODO Auto-generated catch block
showMessage("\nRequest Time Out");
e.printStackTrace();
}
}
private void receivePacket(DatagramPacket packet) {
packet = new DatagramPacket(new byte[PACKET_SIZE], PACKET_SIZE);
try {
socket.receive(packet);
} catch (IOException e) {
// TODO Auto-generated catch block
showMessage("\n Unable to receive packet\n");
e.printStackTrace();
}
showMessage("\n Echoed Message --> "+new String(packet.getData()));
}
private void closeCrap() {
socket.close();
}
private void showMessage(final String data) {
SwingUtilities.invokeLater(
new Runnable() {
@Override
public void run() {
// TODO Auto-generated method stub
chatWindow.append("\n" + data);
}
});
}
}
有人能说出为什么以前的字符会被打印出来吗?
答案 0 :(得分:2)
DatagramPacket.getLength()具有已使用的缓冲区的长度。
尝试
showMessage(new String(packet.getData(), 0, packet.getLength()));
答案 1 :(得分:0)
您反复使用相同的数据包,因此当它从网络读取信息时,它会用新内容覆盖现有的数据包缓冲区内容。客户端没有写入空终止符,因此没有写入缓冲区。因此,当您使用showMessage(new String(packet.getData()));
打印数据时,如果刚刚收到的消息不足以完全覆盖旧内容,则返回的数据仍然会包含旧数据的残余。
它不会回显额外数据,因为当您发送数据包时,套接字服从packet.getLength()
,它控制要发送的字节数。
你可以:
将showMessage调用更改为:
showMessage("\n Echoed Message --> " +
new String(packet.getData(), 0, packet.getLength()));
任何一个都应该解决它。