我正在用 java 中的套接字编写客户端服务器应用程序。客户端和服务器都位于我的计算机上。目标是将消息从客户端发送到服务器。我认为我的套接字没问题，但是我获取消息的方式有问题。也由于某种原因，当我单击连接或启动服务器时，服务器和客户端有时会“卡住”。
这是客户端代码：
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.sql.Time;
import javax.swing.*;
public class Client extends JFrame{
private int connected = 0;
private JTextArea txt;
private JTextField mText;
private JButton sendMessage;
private JScrollPane scroll;
private JButton connect;
private JButton disconnect;
private Socket socket;
private ObjectInputStream input;
private ObjectOutputStream output;
private PrintWriter out;
public Client(){
setLayout(null);
txt = new JTextArea();
scroll = new JScrollPane(txt);
scroll.setBounds(25,10,325,200);
add(scroll);
mText = new JTextField();
mText.setBounds(25,220,250,30);
add(mText);
sendMessage=new JButton("Send");
sendMessage.setBounds(280,220,70,30);
add(sendMessage);
connect= new JButton("Connect");
connect.setBounds(25,260,100,30);
add(connect);
disconnect = new JButton("Disconnect");
disconnect.setBounds(135,260,100,30);
add(disconnect);
//events stuff
eventHandler handler = new eventHandler();
sendMessage.addActionListener(handler);
connect.addActionListener(handler);
disconnect.addActionListener(handler);
}
public class eventHandler implements ActionListener{
public void actionPerformed(ActionEvent e) {
if(e.getSource()==sendMessage){
sendMessage();
}
else
if(e.getSource()==connect){
if(connected==0){
try{
connect();
connected = 1;
}catch(Exception e1){
e1.printStackTrace();
System.out.print(e1);
}
}else
printOnScreen("you are already connected...");
}
else
if(e.getSource()==disconnect){
if(connected==1){
try{
disconnect();
connected = 0;
}catch(Exception e1){
e1.printStackTrace();
System.out.print(e1);
}
}else{printOnScreen("you are not connected");}
}
}
}
public void printOnScreen(String m){
txt.append("\n"+m);
}
public void sendMessage(){
String message = txt.getText();
out.print(message);
}
public void connect() throws UnknownHostException, IOException{
socket=new Socket("localhost",6789);
input = new ObjectInputStream(socket.getInputStream());
output= new ObjectOutputStream(socket.getOutputStream());
out = new PrintWriter(socket.getOutputStream(),true);
out.print("client connecting");
out.flush();
}
public void disconnect() throws IOException{
out.print("Client disconnecting");
out.flush();
out.close();
input.close();
output.close();
socket.close();
}
public static void main(String[]args){
Client cFrame = new Client();
cFrame.setDefaultCloseOperation(EXIT_ON_CLOSE);
cFrame.setSize(385,350);
cFrame.setTitle(" ---___Client1___---");
cFrame.setVisible(true);
}
}
和服务器代码：
import java.awt.Event;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.EventHandler;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.net.*;
import javax.swing.*;
public class Server extends JFrame {
private int running =0;
private JPanel showInformation;
private JButton start;
private JButton stop;
private JTextArea infoArea;
private JScrollPane scroll;
private ServerSocket server;
private Socket client;
private ObjectOutputStream output;
private ObjectInputStream input;
private PrintWriter out;
public Server(){
//setting looks of Frame
setLayout(null);
showInformation=new JPanel();
start = new JButton("Start Server");
stop=new JButton("Stop Server");
infoArea= new JTextArea(20,27);
infoArea.setEnabled(false);
infoArea.setEditable(false);
scroll = new JScrollPane(infoArea);
scroll.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
scroll.setBounds(25,10,325,200);
scroll.setEnabled(true);
add(scroll);
showInformation.setSize(300, 200);
showInformation.setBounds(25,5,325,200);
add(showInformation);
infoArea.setLineWrap(true);
start.setBounds(25,225,150,50);
stop.setBounds(200,225,150,50);
add(start);
add(stop);
//events stuff
eventHandler handler = new eventHandler();
start.addActionListener(handler);
stop.addActionListener(handler);
//sockets
}
public void printOnScreen(String m){
infoArea.append("\n"+m);
}
public class eventHandler implements ActionListener{
public void actionPerformed(ActionEvent e) {
if(e.getSource()==start){
if(running==1)
printOnScreen("Server Already Running !!!");
else
{
try{
startServer();
}catch(Exception e1){
e1.printStackTrace();
System.out.print(e1);
}
running=1;
}
}
else
if(e.getSource()==stop){
if(running==0)
printOnScreen("Server Not Running !!!");
else
{
try{
stopServer();
}catch(Exception e1){
e1.printStackTrace();
System.out.print(e1);
}
running=0;
}
}
}
}
public void startServer() throws IOException{
server = new ServerSocket(6789);
running=1;
Listener ls = new Listener();
ls.run();
client = server.accept();
input = new ObjectInputStream(client.getInputStream());
output = new ObjectOutputStream(client.getOutputStream());
output.flush();
out = new PrintWriter(client.getOutputStream(),true);
out.flush();
printOnScreen("Server Started !!!");
printOnScreen("waiting for connection...");
}
public void stopServer() throws IOException{
output.writeObject("Server Stoped");
output.flush();
input.close();
output.close();
client.close();
server.close();
printOnScreen("Server Stopped");
}
public void getMessage() throws ClassNotFoundException, IOException{
try{
String message = (String)input.readObject();
printOnScreen("client: "+message);
}catch(Exception e){
e.printStackTrace();
}
}
class Listener extends Thread{
public Listener(){
}
public void run(){
try {
client = server.accept();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
System.out.print(e1);
}
while(running==1){
try {
Thread.sleep(4000);
getMessage();
} catch (ClassNotFoundException e) {
e.printStackTrace();
System.out.print(e);
} catch (IOException e) {
e.printStackTrace();
System.out.print(e);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public static void main(String[]args){
Server s = new Server();
s.setDefaultCloseOperation(EXIT_ON_CLOSE);
s.setSize(385, 350);
s.setVisible(true);
s.setTitle(" ----Server----");
s.setTitle("Server Manager");
}
}
这是错误代码：
java.lang.NullPointerException
at Server.getMessage(Server.java:129)
at Server$Listener.run(Server.java:152)
at Server.startServer(Server.java:105)
at Server$eventHandler.actionPerformed(Server.java:73)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)