如何在java中实现TCP服务器和TCP客户端来传输文件

我已经实现了简单的TCP服务器和TCP客户端类，它们可以将消息从客户端发送到服务器，并且消息将在服务器端转换为大写，但是如何实现从服务器到客户端的文件传输以及从客户端到服务器的文件上传呢。以下代码是我得到的

TCPClient.java

：

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

class TCPClient {
 public static void main(String args[]) throws Exception {
        String sentence;
        String modifiedSentence;
        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
        Socket clientSocket = new Socket("127.0.0.1", 6789);
        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        sentence = inFromUser.readLine();
        outToServer.writeBytes(sentence + "\n");
        modifiedSentence = inFromServer.readLine();
        System.out.println("FROM SERVER:" + modifiedSentence);
        clientSocket.close();
    }
}

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

class TCPServer {
    public static void main(String args[]) throws Exception {
        int firsttime = 1;
        while (true) {
            String clientSentence;
            String capitalizedSentence="";
            ServerSocket welcomeSocket = new ServerSocket(3248);
            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            clientSentence = inFromClient.readLine();
            //System.out.println(clientSentence);
            if (clientSentence.equals("set")) {
                outToClient.writeBytes("connection is ");
                System.out.println("running here");
                //welcomeSocket.close();
                //outToClient.writeBytes(capitalizedSentence);
            }
            capitalizedSentence = clientSentence.toUpperCase() + "\n";
            //if(!clientSentence.equals("quit"))
            outToClient.writeBytes(capitalizedSentence+"enter the message or command: ");
            System.out.println("passed");
            //outToClient.writeBytes("enter the message or command: ");
            welcomeSocket.close();
            System.out.println("connection terminated");
        }
    }
}

TCPServer.java

：

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

class TCPClient {
 public static void main(String args[]) throws Exception {
        String sentence;
        String modifiedSentence;
        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
        Socket clientSocket = new Socket("127.0.0.1", 6789);
        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        sentence = inFromUser.readLine();
        outToServer.writeBytes(sentence + "\n");
        modifiedSentence = inFromServer.readLine();
        System.out.println("FROM SERVER:" + modifiedSentence);
        clientSocket.close();
    }
}

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

class TCPServer {
    public static void main(String args[]) throws Exception {
        int firsttime = 1;
        while (true) {
            String clientSentence;
            String capitalizedSentence="";
            ServerSocket welcomeSocket = new ServerSocket(3248);
            Socket connectionSocket = welcomeSocket.accept();
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            clientSentence = inFromClient.readLine();
            //System.out.println(clientSentence);
            if (clientSentence.equals("set")) {
                outToClient.writeBytes("connection is ");
                System.out.println("running here");
                //welcomeSocket.close();
                //outToClient.writeBytes(capitalizedSentence);
            }
            capitalizedSentence = clientSentence.toUpperCase() + "\n";
            //if(!clientSentence.equals("quit"))
            outToClient.writeBytes(capitalizedSentence+"enter the message or command: ");
            System.out.println("passed");
            //outToClient.writeBytes("enter the message or command: ");
            welcomeSocket.close();
            System.out.println("connection terminated");
        }
    }
}

---

因此，首先执行

TCPServer.java

，然后执行

TCPClient.java

，我尝试使用

TCPServer.java

中的if子句来测试用户的输入，现在我真的想实现如何从两侧传输文件（下载和上传）。谢谢。

假设您希望继续支持来回发送邮件和文件

现在，您正在使用writeBytes将数据从客户端发送到服务器

你可以用它来发送任何东西，比如文件的内容

但您需要在客户端和服务器之间定义一个协议，以便它们知道何时传输文件而不是聊天信息

例如，在将文件发送到服务器之前，您可以发送消息/字符串“FILECOMING”，然后服务器就会知道文件的字节数。同样，您也需要一种方法来标记文件的结尾

或者，您可以在每条消息之前发送消息类型

一个性能更高/响应更快的解决方案是在单独的线程/套接字上进行文件传输——这意味着聊天信息不会被传输阻塞。只要需要文件传输，就会为此创建一个新的线程/套接字连接

---

~chris

因此，让我们假设您在服务器端收到了文件名和文件路径。这段代码应该会给你一些想法

服务器

PrintStream out = new PrintStream(socket.getOutputStream(), true);
FileInputStream requestedfile = new FileInputStream(completeFilePath);
byte[] buffer = new byte[1];
out.println("Content-Length: "+new File(completeFilePath).length()); // for the client to receive file
while((requestedfile.read(buffer)!=-1)){
    out.write(buffer);
    out.flush();    
    out.close();    
}
requestedfile.close();

客户

DataInputStream in = new DataInputStream(socket.getInputStream());
int size = Integer.parseInt(in.readLine().split(": ")[1]);
byte[] item = new byte[size];
for(int i = 0; i < size; i++)
    item[i] = in.readByte();
FileOutputStream requestedfile = new FileOutputStream(new File(fileName));
BufferedOutputStream bos = new BufferedOutputStream(requestedfile);
bos.write(item);
bos.close();
fos.close();

DataInputStream in=newdatainputstream（socket.getInputStream（））；
int size=Integer.parseInt（in.readLine（）.split（“：”[1]）；
字节[]项=新字节[大小]；
对于（int i=0；i

理想情况下，您需要使用一些单独的套接字来处理命令。FTP的实现方式是有一个命令通道和一个数据通道。除所有答案外，您还可以使用同时读取任何文件的所有字节，并使用将它们写入任何文件。