如何在Java中使用URL Connection类发送FTP

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;

URL url = new URL("ftp://ftp.example.com/file.txt");

URLConnection connection = url.openConnection();

connection.setRequestProperty("ftp.username", "username");
connection.setRequestProperty("ftp.password", "password");

BufferedInputStream inputStream = new BufferedInputStream(connection.getInputStream());

BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream("local_file.txt"));

byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = inputStream.read(buffer)) != -1) {
    outputStream.write(buffer, 0, bytesRead);
}

8. 关闭输入流和输出流：
```java
inputStream.close();
outputStream.close();

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;

public class FTPExample {
    public static void main(String[] args) {
        try {
            URL url = new URL("ftp://ftp.example.com/file.txt");
            URLConnection connection = url.openConnection();
            connection.setRequestProperty("ftp.username", "username");
            connection.setRequestProperty("ftp.password", "password");
            
            BufferedInputStream inputStream = new BufferedInputStream(connection.getInputStream());
            BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream("local_file.txt"));
            
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            
            inputStream.close();
            outputStream.close();
            
            System.out.println("File downloaded successfully.");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}