好的，以下是我在创建简单的TFTP（普通文件传输协议）程序时使用的2个类。我正在运行一个服务器实例和该程序的客户端实例。我想要完成的是：
客户端连接到服务器并发送它想要的特定文件的消息。服务器定位文件并发送响应（1或0 ... 1表示文件存在，0表示不存在）。然后，服务器将文件的内容发送到客户端应用程序。我试图发送的文件只是简单的文本文件。
现在，我能够收到客户想要的文本文件的名称，但是当我发回回复时，我没有收到任何返回的内容。以下是服务器和客户端都运行的方法。
这是服务器实例
SwingUtilities.invokeLater(new Runnable(){
public void run(){
String fileRequest = UDPReceiver(SERVER_PORT_NUMBER);
outputArea.append("\n" + "File Requested: " + fileRequest + "\n");
outputArea.append("Determining if file exists...\n");
String checkFile = SHARED_DIR + "\\" + fileRequest;
outputArea.append("Checking location: " + checkFile + "\n");
boolean check = fileCheck(checkFile);
if(check == true){
outputArea.append("File location verified..." + "\n");
outputArea.append("Initiating transfer...." + "\n\n");
UDPSender(CLIENT_HOSTNAME, CLIENT_PORT_NUMBER, "1");
}
else{
outputArea.append("File does not exist..." + "\n");
outputArea.append("Exiting run..." + "\n");
}
}
});
客户端实例。
SwingUtilities.invokeLater(new Runnable(){
public void run(){
UDPSender(SERVER_HOSTNAME, SERVER_PORT_NUMBER, FILE_REQUEST);
String message = UDPReceiver(CLIENT_PORT_NUMBER);
outputArea.append("\n\n" + message + "\n");
if(message == "1"){
// File exists
outputArea.append("\n");
outputArea.append("File verified..." + "\n");
outputArea.append("Transfer initiated..." + "\n");
}
else{
// File doesn't exist
outputArea.append("\n");
outputArea.append("File does not exist..." + "\n");
outputArea.append("Terminating connection...");
}
}
});
以下是Sender和Receiver方法。
private void UDPSender(String hostname, String port, String message){
DatagramSocket socket = null;
try{
// Create a datagram socket, look for the first available port
socket = new DatagramSocket();
outputArea.append("Using local port: " + socket.getLocalPort() + "\n");
ByteArrayOutputStream bOut = new ByteArrayOutputStream();
PrintStream pOut = new PrintStream(bOut);
pOut.print(message);
// Convert printstream to byte array
byte[] bArray = bOut.toByteArray();
// Create a DatagramPacket, containing a maximum buffer of 256 bytes
DatagramPacket packet = new DatagramPacket(bArray, bArray.length);
outputArea.append("Looking for hostname " + hostname + "\n");
// Get the InetAddress object
InetAddress remote_addr = InetAddress.getByName(hostname);
// Check its IP Number
outputArea.append("Hostname has IP Address = " + remote_addr.getHostAddress() + "\n");
// Configure the DatagramPacket
packet.setAddress(remote_addr);
packet.setPort(Integer.parseInt(port));
// Send the packet
socket.send(packet);
outputArea.append("Packet sent at: " + new Date() + "\n");
// Display packet information
outputArea.append("Sent by: " + remote_addr.getHostAddress() + "\n");
outputArea.append("Sent from: " + packet.getPort() + "\n");
socket.close();
}
catch(UnknownHostException ue){
outputArea.append("Unknown host: " + hostname + "\n");
outputArea.append("Unknown host: " + ue + "\n");
}
catch(IOException e){
outputArea.append("Error: " + e + "\n");
}
}
private String UDPReceiver(String portNum){
String message = "";
DatagramSocket socket = null;
try{
// Create a DatagramSocket
socket = new DatagramSocket(Integer.parseInt(portNum));
outputArea.append("Listening on local port " + socket.getLocalPort() + "\n");
// Create a DatagramPacket, containing a maximum buffer of 256 bytes
DatagramPacket packet = new DatagramPacket(new byte[256], 256);
// Receive a packet - remember by default this is a blocking operation
socket.receive(packet);
outputArea.append("Packet received at " + new Date() + "\n");
// Display packet information
InetAddress remote_addr = packet.getAddress();
outputArea.append("Sender: " + remote_addr.getHostAddress() + "\n");
outputArea.append("From Port: " + packet.getPort() + "\n");
CLIENT_HOSTNAME = remote_addr.getHostAddress();
//CLIENT_PORT_NUMBER = Integer.toString(packet.getPort());
// Display packet contents, by reading from byte array
ByteArrayInputStream bin = new ByteArrayInputStream(packet.getData());
// Display only up to the length of the original UDP packet
for(int i = 0; i < packet.getLength(); i++){
int data = bin.read();
if(data == -1){
break;
}
else{
message = message + (char)data;
//outputArea.append(Character.toString((char)data));
}
}
socket.close();
return message;
}
catch(IOException e){
outputArea.append("Error: " + e + "\n");
message = "Error: " + e;
return message;
}
}
非常感谢您所提供的任何帮助。我想弄清楚的主要问题是如何让服务器和客户端能够来回发送消息。先谢谢你们。
编辑：
当我运行这个项目时，我现在也在Netbeans中收到错误。我认为它与UDPReceiver方法中的这行代码有关：
socket = new DatagramSocket(Integer.parseInt(portNum));
但我无法弄清楚这有什么问题。
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:454)
at java.lang.Integer.parseInt(Integer.java:527)
at tftp_gui.main.UDPReceiver(main.java:508)
at tftp_gui.main.access$800(main.java:20)
at tftp_gui.main$10.run(main.java:374)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
答案 0 :(得分：0)
你接近是错误的，因为它需要打开客户端端口，无论如何你的特殊问题是因为你找不到文件时你没有发回结果：
检查：
if(check == true){
outputArea.append("File location verified..." + "\n");
outputArea.append("Initiating transfer...." + "\n\n");
UDPSender(CLIENT_HOSTNAME, CLIENT_PORT_NUMBER, "1");
}
else {
outputArea.append("File does not exist..." + "\n");
outputArea.append("Exiting run..." + "\n");
UDPSender(CLIENT_HOSTNAME, CLIENT_PORT_NUMBER, "0"); // here you should send 0
}
此外，您在此处遇到的问题很小：if(message == "1")它应该看起来像if ("1".equals(message))
您的错误是可自行解释的 - 您尚未声明正确的CLIENT_PORT_NUMBER或SERVER_PORT_NUMBER，以下是我用于测试的错误：
private final static String SERVER_PORT_NUMBER = "1234";
private static String CLIENT_HOSTNAME;
private static final String CLIENT_PORT_NUMBER = "2345";
private static final String FILE_REQUEST = "a.txt";
private static final String SHARED_DIR = "d:/";
private static final String SERVER_HOSTNAME = "localhost";