我正在尝试学习java网络编程，但在获取一个简单的聊天程序来连接服务器和主机之间时遇到了困难。以下是我的经历:
当我尝试将客户端程序连接到服务器时，出现空指针异常，并且无法连接。
调试时我发现了这一行
connection.equals(server.accept());
服务器类中的waitForCommuinication()方法没有被执行。
当行
时发生这种情况client = new Socket(InetAddress.getByName(chatServer), 50499);
在客户端类的connectToServer()方法中执行。
我只是使用我的 localhost ip add 运行此代码
服务器类别:
public class Server extends JFrame {
private JTextField enterField;
private JTextArea displayArea;
private ObjectOutputStream output;
private ObjectInputStream input;
private ServerSocket server;
private Socket connection;
private int counter = 1;
public Server() {
super ("Server");
enterField = new JTextField();
enterField.setEditable(true);
enterField.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent event) {
sendData(event.getActionCommand());
enterField.setText("");
}
});
add(enterField, BorderLayout.NORTH);
displayArea = new JTextArea();
add (new JScrollPane(displayArea));
setSize(300,150);
setVisible(true);
}
public void runServer() {
try {
server = new ServerSocket(50499, 100);
//displayMessage("\n Listening on Port: " + server.getLocalPort() + "\n");
while (true) {
try {
waitForCommunication();
getStreams();
processConnection();
} catch (EOFException eofException) {
displayMessage("\n Server terminated connection ");
} finally {
closeConnection();
++counter;
}
}
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
private void closeConnection() {
displayMessage("\nTerminating connection\n");
setTextFieldEditable(false);
try {
output.close();
input.close();
connection.close();
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
private void displayMessage(final String string) {
SwingUtilities.invokeLater(new Runnable(){
@Override
public void run() {
displayArea.append(string);
}
});
}
private void processConnection() throws IOException {
String message = "Connection Sucessful";
sendData(message);
setTextFieldEditable(true);
do {
try {
message = (String) input.readObject();
displayMessage("\n" + message);
} catch (ClassNotFoundException classNotFoundException) {
displayMessage("\nnUnknown object type recieved");
}
} while (!message.equals("Client>>> TERMINATE"));
}
private void setTextFieldEditable(final boolean editable) {
SwingUtilities.invokeLater(new Runnable(){
@Override
public void run() {
enterField.setEditable(editable);
}
});
}
private void getStreams() throws IOException {
output = new ObjectOutputStream(connection.getOutputStream());
output.flush();
input = new ObjectInputStream(connection.getInputStream());
displayMessage("\nGOt I/O stream \n");
}
private void waitForCommunication() throws IOException {
displayMessage("Waiting for cennection \n");
connection.equals(server.accept());
displayMessage("Connection" + counter + " received from: "
+ connection.getInetAddress().getHostName());
}
private void sendData(String message) {
try {
output.writeObject("SERVER>>> " + message);
output.flush();
displayMessage("\nServer>>> " + message);
} catch (IOException ioException){
displayArea.append("\nError Writing Object");
}
}
}
客户类别:
public class Client extends JFrame {
private JTextField enterField;
private JTextArea displayArea;
private ObjectOutputStream output;
private ObjectInputStream input;
private String message = "";
private String chatServer;
private Socket client;
public Client(String host){
super ("Host");
chatServer = host;
enterField = new JTextField();
enterField.setEditable(false);
enterField.addActionListener(new ActionListener(){
@Override
public void actionPerformed(ActionEvent event) {
sendData(event.getActionCommand());
enterField.setText("");
}
});
add(enterField, BorderLayout.NORTH);
displayArea = new JTextArea();
add(new JScrollPane(displayArea));
setSize(300,150);
setVisible(true);
}
public void runClient(){
try{
connectToServer();
getStreams();
processConnection();
} catch (EOFException eofException){
displayMessage("\nClient terminated connection");
} catch (IOException ioException){
ioException.printStackTrace();
} finally {
closeConnection();
}
}
private void closeConnection() {
displayMessage("\nClosing connection");
setTextFieldEditable(false);
try{
output.close();
input.close();
client.close();
} catch (IOException ioException){
ioException.printStackTrace();
}
}
private void displayMessage(final String messageToDisplay) {
SwingUtilities.invokeLater( new Runnable() {
@Override
public void run() {
displayArea.append(messageToDisplay);
}
});
}
private void processConnection() throws IOException {
setTextFieldEditable(true);
do {
try{
message = (String) input.readObject();
} catch (ClassNotFoundException classNotFoundException){
displayMessage("\nUnknown object type recieved");
}
} while (!message.equals("SERVER>>> TERMINATE"));
}
private void setTextFieldEditable(final boolean b) {
SwingUtilities.invokeLater(new Runnable(){
@Override
public void run() {
enterField.setEditable(b);
}
});
}
private void getStreams() throws IOException {
output = new ObjectOutputStream(client.getOutputStream());
output.flush();
input = new ObjectInputStream(client.getInputStream());
displayMessage("\nGot I/O streams!\n");
}
private void connectToServer() throws IOException {
displayMessage("Attempting connection\n");
client = new Socket(InetAddress.getByName(chatServer), 50499);
displayMessage("Connected to: " + client.getInetAddress().getHostName());
}
protected void sendData(String actionCommand) {
try{
output.writeObject("CLIENT>>> " + actionCommand);
output.flush();
displayMessage("\nCLIENT>>> " + actionCommand);
} catch (IOException ioException){
displayArea.append("\nError sending Message");
}
}
}
最佳答案
在Server类中，waitForCommunication方法有NPE，连接原因为空。 connection.equals(server.accept());
我确信您需要类似的东西 connection = server.accept();
关于Java套接字连接问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16677059/