發送文件地址，通過服務器下載程序（Java）

客戶端：

import java.io.*;
import java.net.Socket;
import java.util.Scanner;

/**
 * Created by Administrator on 2020/6/30.
 */
public class socket_file01 {
    public static void main(String[] args) throws IOException {
        File file =getfile();
        Socket socket = new Socket("127.0.0.1",12345);
        BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        PrintStream ps = new PrintStream(socket.getOutputStream());  //輸出流

        ps.println(file.getName());

        String result = br.readLine();
        if("存在".equals(result)){
            System.out.println("上傳的文件已經存在");
            socket.close();
            return;
        }
        FileInputStream fis =new FileInputStream(file);
        byte[] arr =new byte[8192];
        int len;
        while ((len=fis.read(arr))!=-1){
            ps.write(arr,0,len);
        }
        fis.close();
        socket.close();


    }

    private static File getfile() {
        Scanner sc = new Scanner(System.in);
        System.out.println("輸入文件路徑");
        while (true){
            String line = sc.nextLine();
            File file = new File(line);
            if (!file.exists()) {
                System.out.println("文件不存在");
            }else if(file.isDirectory()){
                System.out.println("錄入的爲文件夾");
            }else {
                return file;
            }
        }

    }

}

服務器端：

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * Created by Administrator on 2020/6/30.
 */
public class socket_file02 {
    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(12345) ;
        System.out.println("服務器啓動");
        while (true){
            Socket socket = server.accept();
            new Thread(){
                public void run(){
                    try {
                        InputStream is = socket.getInputStream();
                        BufferedReader br = new BufferedReader(new InputStreamReader(is));
                        PrintStream ps = new PrintStream(socket.getOutputStream());  //輸出流
                        String filename = br.readLine();

                        File dir = new File("updta");
                        dir.mkdir();                      //創建文件夾

                        File file = new File(dir,filename);
                        if(file.exists()){
                            ps.println("存在");
                            socket.close();
                            return;
                        }else{
                            ps.println("不存在");
                        }

                        FileOutputStream fos = new FileOutputStream(file);
                        byte[] arr =new byte[8192];
                        int len;
                        while ((len=is.read(arr))!=-1){
                            fos.write(arr,0,len);
                        }
                        fos.close();
                        socket.close();

                    } catch (IOException e) {
                        e.printStackTrace();
                    }

                }
            }.start();
        }
    }
}