java - 使用 java 套接字从服务器到客户端的文件传输。服务器端错误并且传输到客户端的文件为空

Question

我有一个客户端和服务器，在客户端输入文件名，该文件名将在服务器端的预定义路径下检查，如果文件存在，它将被传输到客户端类似的预定义路径下。我有两个问题:

1)在服务器中，我无法比较给定预定义路径下的文件，因为它显示 FileNotFoundException(没有这样的文件/目录)。

2) 即使出现上述异常，文件也已传输且为空。

这是我的客户端和服务器:

客户端:

import java.io.*;
import java.net.*;
import java.util.*;
public class ft2client
{ 
public static void main(String srgs[])throws IOException
{
Socket s=null;
BufferedReader get=null;
PrintWriter put=null;
try
{ 
s=new Socket("127.0.0.1",8085);
get=new BufferedReader(new InputStreamReader(s.getInputStream()));
put=new PrintWriter(s.getOutputStream(),true);
}  
catch(Exception e)
{
System.exit(0);
}
                    String u,f;
                    System.out.println("Enter the file name to transfer from server:");
                    DataInputStream dis=new DataInputStream(System.in);
                    f=dis.readLine();
                    put.println(f);
                    File f1=new File(f);
                    String str = "/home/user/";
                    FileOutputStream  fs=new FileOutputStream(new File(str,f1.toString()));
                    while((u=get.readLine())!=null)
                    { 
                        byte jj[]=u.getBytes();
                        fs.write(jj);
                    } 
                    fs.close();
                    System.out.println("File received");
                    s.close();
                }      
            }

服务器:

import java.io.*;
import java.net.*;
import java.util.*;
     public class ft2server
             { 
                 public static void main(String args[])throws IOException
                 { 
                     ServerSocket ss=null;
                     try
                     {  
                         ss=new ServerSocket(8085);
                     }
                     catch(IOException e)
                     { 
                         System.out.println("couldn't listen");
                         System.exit(0);
                     }
                     Socket cs=null;
                     try
                     { 
                         cs=ss.accept();
                         System.out.println("Connection established"+cs);
                     }
                     catch(Exception e)
                     { 
                         System.out.println("Accept failed");
                         System.exit(1);
                     } 
                     PrintWriter put=new PrintWriter(cs.getOutputStream(),true);
                     BufferedReader st=new BufferedReader(new InputStreamReader(cs.getInputStream()));
                     String s=st.readLine();
                     String str = "/home/user/Desktop/";
                     String path = str + s; 
                     System.out.println("The requested file is path: "+path);
                     System.out.println("The requested file is : "+s);
                     File f=new File(path);
                     if(f.exists())
                     { 
                         BufferedReader d=new BufferedReader(new FileReader(s));
                         String line;
                         while((line=d.readLine())!=null)
                         {
                             put.write(line);
                             put.flush();
                         }
                         d.close();
                         System.out.println("File transfered");
                         cs.close();
                         ss.close();
                     }  
                 }  
             }

Answer 1

对于二进制数据，您已经更改了读取器，因为它们只能读取字符，不能处理字节流。此外，readline 意味着读到行尾，在二进制文件中('\n')没有太大意义。
这是来自 printWriter 的文档

它不包含写入原始字节的方法，程序应使用未编码的字节流。

您现在想要的是使用字节数组并将它们写为如下所示的 block :

import java.io.*;
import java.net.*;
import java.util.*;
     public class ft2server
         { 

             public static void main(String args[])throws IOException
             { 
                 ServerSocket ss=null;
                 try
                 {  
                     ss=new ServerSocket(8085);
                 }
                 catch(IOException e)
                 { 
                     System.out.println("couldn't listen");
                     System.exit(0);
                 }
                 Socket cs=null;
                 try
                 { 
                     cs=ss.accept();
                     System.out.println("Connection established"+cs);
                 }
                 catch(Exception e)
                 { 
                     System.out.println("Accept failed");
                     System.exit(1);
                 } 
                 BufferedOutputStream put=new BufferedOutputStream(cs.getOutputStream());
                 BufferedReader st=new BufferedReader(new InputStreamReader(cs.getInputStream()));
                 String s=st.readLine();
                 String str = "/home/milind/Desktop/";
                 String path = str + s; 
                 System.out.println("The requested file is path: "+path);
                 System.out.println("The requested file is : "+s);
                 File f=new File(path);
                 if(f.isFile())
                 { 
                     FileInputStream fis=new FileInputStream(f);


                     byte []buf=new byte[1024];
                     int read;
                     while((read=fis.read(buf,0,1024))!=-1)
                     {
                         put.write(buf,0,read);
                         put.flush();
                     }
                     //d.close();
                     System.out.println("File transfered");
                     cs.close();
                     ss.close();
                 }  
             }  
         }

客户端

import java.io.*;
import java.net.*;
import java.util.*;
public class ft2client
{ 
    public static void main(String srgs[])throws IOException
    {
        Socket s=null;
        BufferedInputStream get=null;
        PrintWriter put=null;
        try
        { 
            s=new Socket("127.0.0.1",8085);
            get=new BufferedInputStream(s.getInputStream());
            put=new PrintWriter(s.getOutputStream(),true);

            String f;
            int u;
            System.out.println("Enter the file name to transfer from server:");
            DataInputStream dis=new DataInputStream(System.in);
            f=dis.readLine();
            put.println(f);
            File f1=new File(f);
            String str = "/home/milind/";
            FileOutputStream  fs=new FileOutputStream(new File(str,f1.toString()));
            byte jj[]=new byte[1024];
            while((u=get.read(jj,0,1024))!=-1)
            { 
                fs.write(jj,0,u);
            } 
            fs.close();
            System.out.println("File received");
            s.close();
        }catch(Exception e)
        {
            e.printStackTrace();
            System.exit(0);
        }
    }      
}