你好我有一个我在Java程序中无法识别的问题。 我有一个本地服务器和一个客户端类，我想将输入的值传递给服务器，服务器验证它 但是当我输入用于将值发送到服务器的按钮时，应用程序崩溃了 非常感谢您的帮助。
以下是我的代码：
这是Client.Java
import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.VBox;
import javafx.scene.text.Text;
import javafx.stage.Stage;
import javafx.scene.control.*;
import java.io.IOException;
import java.net.*;
import java.io.PrintWriter;
import java.util.Scanner;
public class Client extends Application // for GUI
{
private PrintWriter outputToServer; // send message to server
private Scanner inputFromServer; // gets response back from the server
//private String username;
private Socket socket;
private static InetAddress host = null;
final int PORT = 1234;
public static void main(String[] args) {
try {
host = InetAddress.getLocalHost();
} catch (UnknownHostException ex) {
System.out.println("Host ID Not Found");
}
do {
launch(args);
} while (true);
}
public void start(Stage stage) throws Exception {
// set up variables
socket = new Socket(host, PORT);
// scanner set up so that it can scan for any input stream (responses) that come from the server
inputFromServer = new Scanner(socket.getInputStream());
outputToServer = new PrintWriter(socket.getOutputStream(), true);
Parent root = FXMLLoader.load(getClass().getResource("welcome.fxml"));
Scene scene;
scene = new Scene(root, 500, 500);
//add the scene to the stage
stage = new Stage();
stage.setScene(scene);
stage.show();
}
@FXML
private TextField Input;
@FXML
private void loginButton (ActionEvent event)
{
String t = Input.getText();
//validateUsername(t);
System.out.println(t);
validateUsername(t);
}
@FXML
private void validateUsername(String username) {
if (username.isEmpty()) {
// message.setText("Please enter your username");
} else {
// send username across to the server
System.out.println(username);
outputToServer.println(username);
String serverRequest = inputFromServer.nextLine();
if (serverRequest.equals("true")) {
LoadClient();
}
}
}
private void LoadClient()
{
Scene scene;
VBox vbox;
Stage stage;
Button inbox = new Button("Inbox");
Button email = new Button("Email");
Button quit = new Button("Quit");
inbox.setOnAction(e -> getInbox());
email.setOnAction(e -> getEmail());
quit.setOnAction(e -> quitApp());
// add buttons to layout
vbox = new VBox();
vbox.getChildren().add(inbox);
vbox.getChildren().add(email);
vbox.getChildren().add(quit);
scene = new Scene(vbox, 500, 500);
stage = new Stage();
stage.setScene(scene);
stage.show();
}
public void getInbox() {
System.out.println("BEFORE SENDING INBOX REQUEST");
outputToServer.println("get_inbox");
System.out.println("AFTER SENDING INBOX REQUEST");
}
public void getEmail() {
outputToServer.println("send_email");
}
public void quitApp() {
outputToServer.println("close");
}
}
这是Server.java
import javafx.fxml.FXML;
import java.io.IOException;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.net.ServerSocket;
import java.util.ArrayList;
import java.net.*;
import java.io.*;
import java.util.Scanner;
public class Server implements Serializable // used to send object from client to server
{
// list of users of type string
private static ArrayList<String> users = new ArrayList<String>();
private static ArrayList<Email> mails = new ArrayList<Email>();
public static void main(String[] args) throws IOException
{
// set up 3 users
users.add("U1");
users.add("U2");
users.add("U3");
Socket client; // client
ServerSocket serverSocket = null; // server
final int PORT = 1234;
ClientHandler clientHandler;
// set up the server socket
try
{
serverSocket = new ServerSocket(1234);
}
catch (IOException ioEx)
{
System.out.println("Can't set up port");
System.exit(1);
}
System.out.println("\n Server running");
do {
client = serverSocket.accept(); // accept the client to the server
// create a function that will validate the user
String validUser = validateUser(client);
clientHandler = new ClientHandler(validUser, client);
clientHandler.start(); // calls the run function
} while (true);
}
private static String validateUser(Socket client)
{
Scanner inputFromClient = null;
PrintWriter outputToClient = null;
boolean validUser = false;
try
{
// allows the server to retrieve the input from the client
inputFromClient = new Scanner(client.getInputStream());
// allow server to send things to the client
outputToClient = new PrintWriter(client.getOutputStream(), true);
}
catch(IOException io)
{
System.out.println("Problem initialising variables");
}
// get the input from the client
String userToValidate = inputFromClient.nextLine();
while (validUser == false)
{
for(String username : users)
{
// check the user to validate matches the user from the client
if (username.equals(userToValidate))
{
// tell the client that user is valid
validUser = true;
break;
}
}
if(validUser == false)
{
// user is invalid so wait for a new user to pass from the client to the server
outputToClient.println("false");
userToValidate = inputFromClient.nextLine();
}
else
{
outputToClient.println("true");
}
}
// return the correct username
return userToValidate;
}
// get the mail from the server so it can be accessed in the clienthandler
private static ArrayList<Email> getMail()
{
return mails;
}
}
// each client will have their unique username
class ClientHandler extends Thread implements Serializable
{
private Socket client;
// retrieve requests from the client
private Scanner input;
// send requests to the client
private PrintWriter output;
private String username;
public ClientHandler(String username, Socket client)
{
this.username = username;
this.client = client;
System.out.println("BEFORE TRY");
try
{
input = new Scanner(client.getInputStream());
output = new PrintWriter(client.getOutputStream(), true);
}
catch(IOException io)
{
System.out.println("Client Handler not set up properly");
}
}
public void run()
{
// recieve request from the server
String request = input.nextLine();
System.out.println(request);
// check the request
while(!request.equals("close"))
{
// do whatever the user wants to do
if (request.equals("get_inbox"))
{
System.out.println("INSIDE INBOX REQUEST");
}
else if (request.equals("send_email"))
{
System.out.println("INSIDE SEND EMAIL REQUEST");
}
request = input.nextLine(); // get new request from server
}
// end the client connection
try
{
System.out.println("Ending connection");
client.close();
}
catch(IOException io)
{
System.out.println("Coulnd't close connection");
}
}
}
错误日志是：
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run( GlassViewEventHandler.java:381)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run( GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354 (GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolki t.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewE ventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImp l.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 45 more
Caused by: java.lang.NullPointerException
at Client.validateUsername(Client.java:112)
at Client.loginButton(Client.java:99)
... 55 more
答案 0 :(得分：0)
非常感谢James_D，因为outputToServer没有初始化。 正确的代码是：
private void loader(){
try
{
socket = new Socket(host, PORT);
inputFromServer = new Scanner(socket.getInputStream());
outputToServer = new PrintWriter(socket.getOutputStream(),true);
}
catch (IOException e)
{
e.printStackTrace();
return;
}
if(this.outputToServer == null)
{
System.out.println("NULL OUTPUT TO SERVER");
}
}
然后在loginButton中调用它：
@FXML
private void loginButton(ActionEvent event) throws IOException
{
if (outputToServer == null)
System.out.println("NULL IN LOGIN BUTTON FUNCTION");
String t = Input.getText();
//validateUsername(t);
System.out.println(t);
loader();
validateUsername(t);
}