Ftp

Introduction

The FTP client encapsulation is based on Apache Commons Net.

Usage

Adding Dependencies

<dependency>
 <groupId>commons-net</groupId>
 <artifactId>commons-net</artifactId>
 <version>3.6</version>
</dependency>

Using the FTP Client

// Anonymous login (FTP server without username and password)
Ftp ftp = new Ftp("172.0.0.1");
// Enter remote directory
ftp.cd("/opt/upload");
// Upload local file
ftp.upload("/opt/upload", FileUtil.file("e:/test.jpg"));
// Download remote file
ftp.download("/opt/upload", "test.jpg", FileUtil.file("e:/test2.jpg"));

// Close the connection
ftp.close();

Active Mode and Passive Mode

• PORT (Active Mode)

The FTP client connects to the FTP server’s port 21, sends the username and password to log in. After a successful login, when it needs to list or read data, the client randomly opens a port (above 1024), sends the PORT command to the FTP server, telling the server that the client is using active mode and has opened a port. The FTP server receives the active mode command and port number, and connects to the client’s opened port through its port 20 to send data.

• PASV (Passive Mode)

The FTP client connects to the FTP server’s port 21, sends the username and password to log in. After a successful login, when it needs to list or read data, it sends the PASV command to the FTP server. The server randomly opens a port (above 1024) locally, and then tells the client the opened port number. The client then connects to the server’s opened port for data transmission.

For more information, see: https://www.cnblogs.com/huhaoshida/p/5412615.html

By default, Ftp uses passive mode. To switch to active mode:

Ftp ftp = new Ftp("172.0.0.1");

// Switch to active mode
ftp.setMode(FtpMode.Active);