java tcp错误需要修复

Question

我编写了两个类作为客户端和服务器，它们可以双向传输文件，有一些错误，第一个错误是当我选择从客户端上传文件到服务器时，文件可以成功上传，但是，服务器进程将被 InputStream pis = connectionSocket.getInputStream(); 的空指针异常停止； 第二个BUG是当你下载成功了，想再试一次，文件不能正常传输，但是第三次​​下载，又能正常运行了，奇怪。下面的代码就是我所拥有的，当它要求您输入文件名时，您必须输入类似 c:\users\file.file 的内容。希望有人可以帮助我，非常感谢。 tcpserver.java

 import java.io.*;
 import java.net.*;

 class TCPServer {

public static void main(String args[]) {
    String direction="";
    String filename="";
    byte[] aByte = new byte[1];
    int bytesRead;

    while (true) {
        ServerSocket welcomeSocket = null;
        Socket connectionSocket = null;
        BufferedOutputStream outToClient = null;
        BufferedReader inFromClient =null;

        try {
            welcomeSocket = new ServerSocket(3248);
            connectionSocket = welcomeSocket.accept();
            outToClient = new BufferedOutputStream(connectionSocket.getOutputStream());
            System.out.println("connection is established with               "+connectionSocket.getInetAddress()+"using port "+connectionSocket.getPort());
             inFromClient =new BufferedReader(
 new InputStreamReader(connectionSocket.getInputStream()));

             direction = inFromClient.readLine();
             System.out.println("client wants to "+direction);
             filename=inFromClient.readLine();
             System.out.println("file directory and name is "+filename);



        } catch (IOException ex) {
            // Do exception handling
        }

        if (outToClient != null&&direction.equals("download")) {
            File myFile = new File(filename);
            byte[] mybytearray = new byte[(int) myFile.length()];

            FileInputStream fis = null;

            try {
                fis = new FileInputStream(myFile);
            } catch (FileNotFoundException ex) {
                System.out.println("can't find file");
                // Do exception handling
            }
            BufferedInputStream bis = new BufferedInputStream(fis);

            try {
                bis.read(mybytearray, 0, mybytearray.length);
                outToClient.write(mybytearray, 0, mybytearray.length);
                outToClient.flush();
                outToClient.close();
                connectionSocket.close();
                fis.close();
                bis.close();
                inFromClient.close();


            } catch (IOException ex) {
                // Do exception handling
            }
        }
        if(direction.equals("upload"))
        {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            //byte[] yourByteArray = new byte[10240];
            File serverFile = new File(filename);
            FileOutputStream fos = null;
        BufferedOutputStream bos = null;

         try {
            InputStream pis = connectionSocket.getInputStream();
            fos = new FileOutputStream(filename);
            bos = new BufferedOutputStream(fos);
            bytesRead = pis.read(aByte, 0, aByte.length);

            do {
                    baos.write(aByte);
                    bytesRead = pis.read(aByte);
            } while (bytesRead != -1&&aByte!=null);

            bos.write(baos.toByteArray());
            bos.flush();
            bos.close();
            //clientSocket.close();
        } catch (IOException ex) {
            // Do exception handling
        }

        System.out.println("The file transmission finishes!");

    }
}
}

}

TCPClient.java

    import java.io.*;

   import java.io.ByteArrayOutputStream;
     import java.net.*;
     import java.util.*;

class TCPClient {

public static void main(String args[]) {
    byte[] aByte = new byte[1];
    int bytesRead;
    String downloadfile;
    String downloadfilere;
    String uploadfile;
    String uploadfilese;
    Socket clientSocket = null;
    InputStream is = null;
    String ip;
    int port;
    String conti;

    boolean goon=true;
    int situation;
    Scanner sc=new Scanner(System.in);
    Scanner sc1=new Scanner(System.in);
    Scanner sc2=new Scanner(System.in);
    System.out.println("please input the ip address for the host");
    ip=sc.nextLine();
    System.out.println("please input the port number");
    port=sc.nextInt();
    DataOutputStream outToServer=null;
    BufferedOutputStream fileoutToServer = null;



    while(goon=true){
    try {
        clientSocket = new Socket(ip, port);
        is = clientSocket.getInputStream();
        System.out.println("connection is established");
         outToServer = new DataOutputStream(clientSocket
.getOutputStream());
    } catch (IOException ex) {
        // Do exception handling
    }

    System.out.println("what request do you want to make:    "+"\n"+"1.download"+"\n"+"2.upload");
    situation=sc.nextInt();
    if(situation==1){
       try{ outToServer.writeBytes("download"+ "\n");
       outToServer.flush();}catch(IOException ex){}
        System.out.println("please enter the file name for download");
        downloadfile=sc1.nextLine();
        //try{ outToServer.writeBytes("download"+ "\n");}catch(IOException ex){}
        System.out.println("please enter the file name you want the received file to be saved as");
       downloadfilere=sc2.nextLine();
       try{ outToServer.writeBytes(downloadfile+ "\n");
       outToServer.flush();
       }catch(IOException ex){}

    if(downloadfile!=""){
    ByteArrayOutputStream baos = new ByteArrayOutputStream();

    if (is != null) {

        FileOutputStream fos = null;
        BufferedOutputStream bos = null;
        try {
            fos = new FileOutputStream(downloadfilere);
            bos = new BufferedOutputStream(fos);
            bytesRead = is.read(aByte, 0, aByte.length);

            do {
                    baos.write(aByte);
                    bytesRead = is.read(aByte);
            } while (bytesRead != -1);

            bos.write(baos.toByteArray());
            bos.flush();
            bos.close();
            clientSocket.close();
        } catch (IOException ex) {
            // Do exception handling
        }
    }}
    System.out.println("file received successfully");
    }
    if(situation==2)
    {
        try{ outToServer.writeBytes("upload"+ "\n");}catch(IOException ex){}
        System.out.println("please enter the file name for upload");
        uploadfile=sc1.nextLine();
        System.out.println("please enter the file name on server for upload");
        uploadfilese=sc2.nextLine();
        try{ outToServer.writeBytes(uploadfilese+ "\n");}catch(IOException ex){}

        File myFile = new File(uploadfile);
        byte[] yourByteArray = new byte[1024];//*
        try{
          FileInputStream pfis = new  FileInputStream(myFile);
         //BufferedInputStream bbis=new BufferedInputStream(pfis);
         int pnread=0;
        OutputStream pbos = clientSocket.getOutputStream();
                       //System.out.println("pfis.read(yourByteArray)"+pfis.read(yourByteArray));//***
           while((pnread=pfis.read(yourByteArray))>0)
        {
         pbos.write(yourByteArray, 0, pnread);
        //System.out.println("pfis.read(yourByteArray)"+pnread);//***
           pbos.flush();
          }
          pbos.close();
        }catch(IOException ex){}


    }

    System.out.println("do you want to do another request?");
    conti=sc.nextLine();
    if(conti.equals("yes"))
        goon=true;
    else 
        goon=false;
    //try{clientSocket.close();}catch(IOException ex){}
}
}

}

错误信息：

    Exception in thread "main" java.lang.NullPointerException
    at TCPServer.main(TCPServer.java:79)
    Java Result: 1

Answer 1

一个空指针异常来自 输入流 pis = connectionSocket.getInputStream()

所以“connectionSocket”为空。发生这种情况是因为您不正确的执行处理结构。考虑如果您未能构造“connectionSocket”然后在 catch 块之后继续执行代码会发生什么。所有使用 'connectionSocket' 的代码都应该在构造它的 'try' 块内。

您还忽略了 read() 方法的结果，并假设它返回了最大可能的数据量。没有指定这样做。你应该有这样的东西：

int count;
while ((count = in.read(buffer)) > 0)
  out.write(buffer, 0, count);

Answer 2

我怀疑问题在于您调用了两次connectionSocket.getInputStream。您应该只获取一次流并在连接过程的整个生命周期内使用它。

这无关紧要，但是为什么客户端类中有三个Scanner 实例？你只需要一个。它们都从同一个底层流 (System.in) 中读取。