所以我尝试将我的代码与DataInputStream
和BufferedReader
一起使用
将字符串从客户端发送到服务器,并已在Internet上查找资源以寻求解决方案。我正在使用从客户端读取字符串的方法,并且每次都始终显示NullPointerException。这是服务器端代码的副本:
package WOF;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class TheBoard {
private int port;
Socket client;
public TheBoard(int port)
{
this.port = port;
}
public void start() throws IOException
{
System.out.println("Now Determining if guess is correct");
ServerSocket serverSocket = new ServerSocket(port);
Socket client = serverSocket.accept();
sendWelcomeMessage(client);
}
private void sendWelcomeMessage(Socket client) throws IOException
{
DataOutputStream out = new DataOutputStream(client.getOutputStream());
out.writeBytes("Hello, You are now Playing Wheel of Fortune, Command Line Style!!");
}
public void getGuess(Socket client) throws IOException
{
String userInput;
DataInputStream getGuessFromClient = new DataInputStream(client.getInputStream()); //NPE Occurs Right on this Line.
System.out.println(getGuessFromClient);
userInput = getGuessFromClient.readUTF();
System.out.println("Guess is: " + userInput);
}
public static void main(String[] args) {
int portNumber = 9990;
try
{
TheBoard socketServer = new TheBoard(portNumber);
socketServer.start();
socketServer.getGuess(socketServer.client); //This Throws an NPE
}
catch (IOException e)
{
System.err.println("UH OH!! Can't Connect.." + e.getMessage());
}
}
}
我在发生堆栈跟踪的代码中进行了注释,并做了很多我自己的故障排除,但似乎无法超越创建getGuessFromClient的那一行。我确定这是一个简单的解决方案,但是我的研究空手而归。有没有人有什么建议?
顺便说一下,这是堆栈跟踪:
Now Determining if guess is correct
Exception in thread "main" java.lang.NullPointerException
at WOF.TheBoard.getGuess(TheBoard.java:40)
at WOF.TheBoard.main(TheBoard.java:52)
最佳答案
代替
Socket client = serverSocket.accept();
使用:
client = serverSocket.accept();
您正在将客户端分配给本地变量,而不是成员变量,因此您当前在取消引用成员变量之前未分配成员变量。
关于java - DataOutputStream不断给出空指针异常,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/32732162/