我正在尝试创建一个程序，其中客户端和服务器相互发送文本消息(以 utf-8 字符串格式)，类似于两部手机相互发送文本消息的方式。最终我需要创建四行(两行用于在服务器端编码/解码 utf-8 字符串)(两行用于在客户端编码/解码 utf-8 字符串)该程序使用两个线程，一个用于客户端，一个用于服务器.
Mac 终端错误的屏幕截图(命令提示符)
在更改以下代码行之前没有错误:
String MessageFromClientEncodedUTF8 = "";
BufferedReader BufReader1 = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String MessageFromClientDecodedFromUTF8 = BufReader1.readLine();
System.out.println("The message is currently encoded UTF-8");
byte[] bytes = MessageFromClientEncodedUTF8.getBytes("UTF-8");
String MessageFromClientDecodedUTF8 = new String(bytes, "UTF-8");
System.out.println("Message received from client (decoded utf-8): "+ MessageFromClientDecodedUTF8);
共有三个文件:主函数文件、服务器文件、客户端文件。当主函数文件运行时，如果存在“-l”命令行参数，则运行服务器文件，否则运行客户端。
服务器文件(DirectMessengerServer.java):
import java.io.*;
import java.net.*;
import java.util.*;
import static java.nio.charset.StandardCharsets.*;
public class DirectMessengerServer
{
private static Socket socket;
boolean KeepRunning = true;
void ServerRun(String[] args)
{
Thread Server = new Thread ()
{
public void run ()
{
System.out.println("Server thread is now running");
try
{
System.out.println("Try block begins..");
int port_number1= Integer.valueOf(args[1]);
System.out.println("Port number is: " + port_number1);
ServerSocket serverSocket = new ServerSocket(port_number1);
//SocketAddress addr = new InetSocketAddress(address, port_number1);
System.out.println( "Listening for connections on port: " + ( port_number1 ) );
while(KeepRunning)
{
//Reading the message from the client
String MessageFromClientEncodedUTF8 = "";
BufferedReader BufReader1 = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String MessageFromClientDecodedFromUTF8 = BufReader1.readLine();
System.out.println("The message is currently encoded UTF-8");
byte[] bytes = MessageFromClientEncodedUTF8.getBytes("UTF-8");
String MessageFromClientDecodedUTF8 = new String(bytes, "UTF-8");
System.out.println("Message received from client (decoded utf-8): "+ MessageFromClientDecodedUTF8);
//Shut down with zero-length message
if(MessageFromClientDecodedFromUTF8.equals(""))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8.equals(null))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8=="")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8==null)
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
if(MessageFromClientDecodedFromUTF8=="\n")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
serverSocket.close();
}
//creating message to server send from standard input
String newmessage = "";
try {
// input the message from standard input
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
String line = "";
System.out.println( "Standard input (press enter then control D when finished): " );
while( (line= input.readLine()) != null && KeepRunning==true )
{
newmessage += line + " \n ";
}
}
catch ( Exception e ) {
System.out.println( e.getMessage() );
}
//Writing return message back to client
String returnMessage = newmessage;
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write(returnMessage + "\n");
System.out.println("Message sent to client: "+returnMessage);
bw.flush();
}
}
catch ( Exception e )
{
e.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
};
Server.start();
}
}
客户端文件(DirectMessengerClient.java):
import java.io.*;
import java.net.*;
import java.util.*;
import static java.nio.charset.StandardCharsets.*;
public class DirectMessengerClient
{
boolean KeepRunning = true;
private static Socket socket;
//static String[] arguments;
//public static void main(String[] args)
//{
// arguments = args;
//}
public DirectMessengerClient()
{
//System.out.println("test.");
}
public void ClientRun(String[] args)
{
Thread Client = new Thread ()
{
public void run()
{
System.out.println("Client thread is now running");
try
{
System.out.println("Try block begins..");
String port_number1= args[0];
System.out.println("Port number is: " + port_number1);
int port = Integer.valueOf(port_number1);
System.out.println("Listening for connections..");
System.out.println( "Listening on port: " + port_number1 );
while(KeepRunning)
{
String host = "localhost";
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);
//Send the message to the server
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
//creating message to send from standard input
String newmessage = "";
try
{
// input the message from standard input
BufferedReader input= new BufferedReader(
new InputStreamReader(System.in));
String line = "";
System.out.println( "Standard input (press enter then control D when finished): " );
while( (line= input.readLine()) != null )
{
newmessage += line + " ";
}
}
catch ( Exception e )
{
System.out.println( e.getMessage() );
}
String sendMessage = newmessage;
bw.write(sendMessage + "\n"); // <--- ADD THIS LINE
bw.flush();
System.out.println("Message sent to server: "+sendMessage);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String MessageFromServer = br.readLine();
System.out.println("Message received from server: " + MessageFromServer);
if(MessageFromServer.equals(""))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer.equals(null))
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer=="")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer==null)
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
if(MessageFromServer=="\n")
{
KeepRunning=false;
System.out.println("Shutting down");
System.exit(0);
socket.close();
}
}
}
catch ( Exception e )
{
e.printStackTrace();
}
finally
{
//Closing the socket
try
{
socket.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
};
Client.start();
}
}
主要功能文件(DirectMessengerCombined.java):
public class DirectMessengerCombined
{
public static void main(String[] args)
{
DirectMessengerClient Client1 = new DirectMessengerClient();
DirectMessengerServer Server1 = new DirectMessengerServer();
for (int i = 0; i < args.length; i++)
{
if(!args[0].equals("-l"))
{
Client1.ClientRun(args);
}
switch (args[0].charAt(0))
{
case '-':
if(args[0].equals("-l"))
{
Server1.ServerRun(args);
}
}
i=args.length + 20;
}
}
}
我的问题是:如何更改字符串的编码或解码方式，以便将字符串发送到另一端或如何解决空指针异常错误？
最佳答案
这是因为您试图在套接字存在之前获取它的输入流:-
BufferedReader BufReader1 = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"));
socket = serverSocket.accept();
这两行应该相反。 :)
编辑:进一步查看您的代码，您正在创建 BufReader1 (这导致了错误)，然后以完全相同的方式创建 br ，即两者都是套接字的BufferedReader。你只需要一个；有两个可能会给读者带来问题。
关于尝试将字符串编码/解码为 UTF-8 后引发 Java 服务器线程空指针异常错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43327679/