在我的代码中找不到问题。简单的服务器/客户端程序。谷歌搜索错误没有任何成功。添加完整代码只是为了确定，虽然问题似乎是在服务器类的最开始。
输出：
Server listening
Client has connected
Exception in thread "Thread-0" java.lang.NullPointerException
at Server.TCPServer.run(TCPServer.java:44)
at java.lang.Thread.run(Thread.java:745)
BUILD STOPPED (total time: 6 seconds)
TCPServer.java
public class TCPServer implements Runnable {
Socket clientSocket;
Boolean connected;
TCPServer(Socket clientScoket, Boolean connected) {
this.clientSocket = clientSocket;
this.connected = connected;
}
public static void main(String args[])
throws Exception {
ServerSocket server = new ServerSocket(1234);
System.out.println("Server listening");
while (true) {
Socket client = server.accept();
System.out.println("Client has connected");
new Thread(new TCPServer(client, true)).start();
}
}
@Override
public void run() {
InputStream clientIn;
try {
clientIn = clientSocket.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(clientIn));
OutputStream outToClient = clientSocket.getOutputStream();
PrintWriter pw = new PrintWriter(outToClient, true);
while (true) {
try {
int day, month, year;
int second, minute, hour;
GregorianCalendar date = new GregorianCalendar();
day = date.get(Calendar.DAY_OF_MONTH);
month = date.get(Calendar.MONTH) + 1;
year = date.get(Calendar.YEAR);
second = date.get(Calendar.SECOND);
minute = date.get(Calendar.MINUTE);
hour = date.get(Calendar.HOUR);
String msgFromClient = br.readLine();
System.out.println("Message received from client = " + msgFromClient);
// Send response to the client
//OutputStream clientOut = client.getOutputStream();
//PrintWriter pw = new PrintWriter(clientOut, true);
if ("time".equalsIgnoreCase(msgFromClient)) {
String ansMsg = "Current time is " + hour + " : " + minute + " : " + second;
pw.println(ansMsg);
} else if ("date".equalsIgnoreCase(msgFromClient)) {
String ansMsg = "Current date is " + year + "-" + month + "-" + day;
pw.println(ansMsg);
} else if ((msgFromClient).contains("c2f")) {
String ansMsg = "Temprature in fahrenheit: ";
String[] result = msgFromClient.split(",");
double value = Double.parseDouble(result[1]) * 1.8 + 32;
pw.println(ansMsg + value);
} else if ((msgFromClient).contains("max")) {
double max = 0;
String ansMsg = "Biggest number is: ";
String[] result = msgFromClient.split(",");
for (int counter = 1; counter < result.length; counter++) {
if (Double.parseDouble(result[counter]) > max) {
max = Double.parseDouble(result[counter]);
}
}
pw.println(ansMsg + max);
} else if ((msgFromClient).contains("sum")) {
double sum = 0;
String ansMsg = "The sum of the numbers is: ";
String[] result = msgFromClient.split(",");
for (int counter = 1; counter < result.length; counter++) {
sum = Double.parseDouble(result[counter]) + sum;
}
pw.println(ansMsg + sum);
} else if ((msgFromClient).contains("dload")) {
pw.println(getDload(msgFromClient, outToClient));
}
// Close sockets
if (msgFromClient != null && msgFromClient.equalsIgnoreCase("bye")) {
String response = "Bye!";
System.out.println(response);
pw.println(response);
pw.close();
clientSocket.close();
break;
}
} catch (IOException ie) {
}
}
} catch (IOException ex) {
Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
} finally {
//try {
//clientIn.close();
//} catch (IOException ex) {
///Logger.getLogger(TCPServer.class.getName()).log(Level.SEVERE, null, ex);
//}
}
}
private OutputStream getDload(String msgFromClient, OutputStream outToClient) throws FileNotFoundException, IOException {
String[] fileName = msgFromClient.split(",");
File myFile = new File("ToSend\\" + fileName[1]);
System.out.println("File exists: " + myFile.exists());
if (!myFile.exists()) {
String response = "Could not find file!";
//pw.println(response);
outToClient.write(response.getBytes("UTF-8"));
} else {
outToClient.write("Incoming File\n".getBytes("UTF-8"));
String fileLength = String.valueOf(myFile.length());
System.out.println("File length in bytes :" + fileLength);
byte[] mybytearray = new byte[(int) myFile.length()];
FileInputStream fis = new FileInputStream(myFile);
BufferedInputStream bis = new BufferedInputStream(fis);
bis.read(mybytearray, 0, mybytearray.length);
outToClient.write(mybytearray, 0, mybytearray.length);
}
return outToClient;
}
}
TCPClient.java
public class TCPClient {
private final String fileOutput = "C:\\testout.txt";
public static void main(String args[]) {
Socket client = null;
int portnumber = 1234; // Default port number we are going to use
if (args.length >= 1) {
portnumber = Integer.parseInt(args[0]);
}
byte[] aByte = new byte[1];
int bytesRead;
for (int i = 0; i < 10; i++) {
try {
String msg = "";
// Create a client socket
client = new Socket(InetAddress.getLocalHost(), portnumber);
//System.out.println("Client socket is created " + client);
// Create an output stream of the client socket
BufferedOutputStream clientOut = new BufferedOutputStream(client.getOutputStream());
PrintWriter pw = new PrintWriter(clientOut, true);
// Create an input stream of the client socket
InputStream clientIn = client.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(clientIn));
// Create BufferedReader for a standard input
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter command. Type Bye to exit. ");
// Read data from standard input device and write it
// to the output stream of the client socket.
msg = stdIn.readLine().trim();
pw.println(msg);
// Stop the operation
if (msg.equalsIgnoreCase("Bye")) {
break;
}
if (msg.contains("dload")) {
//msg.trim();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
FileOutputStream fos = null;
BufferedOutputStream bos = null;
String[] fileName = msg.split(",");
long start = System.currentTimeMillis();
File newFile = new File("Received\\" + fileName[1]);
try {
fos = new FileOutputStream(newFile);
bos = new BufferedOutputStream(fos);
bytesRead = clientIn.read(aByte, 0, aByte.length);
do {
baos.write(aByte);
bytesRead = clientIn.read(aByte);
} while (bytesRead != -1);
bos.write(baos.toByteArray());
bos.flush();
bos.close();
System.out.println("\nTransfer completed in: " + (System.currentTimeMillis() - start) + " ms.");
} catch (IOException ex) {
ex.printStackTrace();
}
} else {
// Read data from standard input device and write it to the
// output stream of the client socket.
pw.println(msg);
}
// Read data from the input stream of the client socket.
System.out.println("Message returned from the server = " + br.readLine());
pw.close();
br.close();
client.close();
} catch (IOException ie) {
System.out.println("I/O error " + ie);
}
}
}
}