Cliente que manda um arquivo pela rede e servidor que recebe este arquivo.

ClienteSocketArquivo.java

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintStream;
import java.net.Socket;
import java.util.Scanner;

public class ClienteSocketArquivo {
    
    public static void main(String[] args) throws IOException {
        
        Socket cliente = new Socket("127.0.0.1", 12345);
        
        System.out.println("Cliente se conectou ao servidor"); 
        
        InputStream is = new FileInputStream("arquivo.txt");
        Scanner scanner = new Scanner(is);
        PrintStream saida = new PrintStream(cliente.getOutputStream());
        
        while(scanner.hasNextLine()){
            saida.println(scanner.nextLine());
        }
        
        scanner.close();
        saida.close();
        is.close();
    }
    
}

ServidorSocketRecebido.java

import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Scanner;

public class ServidorSocketRecebido {
    
    public static void main(String[] args) throws IOException {
        
        ServerSocket servidor = new ServerSocket(12345);
        System.out.println("Servidor aguardando na porta 12345"); 
        
        Socket cliente = servidor.accept();
        System.out.println("Cliente " + cliente.getInetAddress().getHostAddress() + " se conectou");
        
        Scanner scanner = new Scanner(cliente.getInputStream());
        
        OutputStream os = new FileOutputStream("recebido.txt");
        OutputStreamWriter osw = new OutputStreamWriter(os);
        BufferedWriter buffer = new BufferedWriter(osw);
        while(scanner.hasNextLine()){
            
            buffer.write(scanner.nextLine());
            buffer.newLine();
        }
        
        buffer.close();
        scanner.close();
        servidor.close();
    }
    
}