File upload and download based on FTP protocol

FTP Protocol

FTP protocol is built on top of TCP protocol and is a common protocol for file transfer services. It adopts C/S mode and is an application layer protocol for file transfer between client and server on computer network.

(For TCP protocol, please refer to: http://t.csdn.cn/6a78D)

Simple use of FTP server

Before using, we need to install an FTP server (easyftp server) on the computer and open it as shown below:

Then we need to create an account, set the login name and password, and set the FTP server in the F:\\run\\FTP directory, so that the files we upload later will be displayed in this directory, and the download will alsoFiles will be looked for in this directory.This directory is our server location.

FTP server connection

1. Create FTP client object

2. Connect through the server's IP address and port number

3. Login with username and password

4. Disconnect after the FTP server is used up

import java.io.FileInputStream;import java.io.IOException;import org.apache.commons.net.ftp.FTPClient;public class Test {public static void main(String[] args) {//FTP client objectFTPClient ftpClient = new FTPClient();//step1: connect to FTP serverftpClient.connect("192.168.254.185", 21);//step2: loginftpClient.login("admin", "admin");} catch (IOException e) {e.printStackTrace();}finally {try {//After use, you need to disconnect the FTP serverftpClient.disconnect();} catch (IOException e) {e.printStackTrace();}}}}

File upload in FTP server

1. Connect to FTP server

2. Create an input stream of a local file and read a local file

3. Set the file type to set the file to binary

4. Upload ftpClient.storeFile("zym.jpg", localIn ), pass in the file name and the file stream to be uploaded

5. Disconnect

import java.io.FileInputStream;import java.io.IOException;import org.apache.commons.net.ftp.FTPClient;public class Test {public static void main(String[] args) {//FTP client objectFTPClient ftpClient = new FTPClient();try(FileInputStream localIn = new FileInputStream("E:\\run\\IO stream\\image\\tj.jpg")){//step1: connect to FTP serverftpClient.connect("192.168.254.185", 21);//step2: loginftpClient.login("admin", "admin");//step3: Operation//Check if the directory existsboolean isChange = ftpClient.changeWorkingDirectory("zym");System.out.println("Switch working directory 1:" + isChange);if(!isChange) {//create the directory if it doesn't existftpClient.makeDirectory("zym");isChange = ftpClient.changeWorkingDirectory("zym");}System.out.println("Switch working directory 2:" + isChange);//Store files (upload local files to FTP server)//Parameter 1: The storage location of the ftp server (directory + file name)//parameter 2: local file input streamftpClient.setFileType(FTPClient.BINARY_FILE_TYPE);//Set the file type before savingftpClient.storeFile("zym.jpg",localIn );//Store} catch (IOException e) {e.printStackTrace();}finally {try {ftpClient.disconnect();} catch (IOException e) {e.printStackTrace();}}}}

File download from FTP server

1. Connect to FTP server

2. Create an output stream and determine the download location

3. Set the file type to set the file to binary

4. Download ftpClient.retrieveFile(downlaodFileName, download), pass in the download file name, and the path to be downloaded

5. Disconnect

import java.io.FileOutputStream;import java.io.IOException;import java.net.SocketException;import org.apache.commons.net.ftp.FTPClient;public class FtpDownLoad {public static void main(String[] args) {//Create FTP clientFTPClient ftpClient = new FTPClient();// file to downloadString downlaodFileName = "tj.jpg";try (FileOutputStream download = new FileOutputStream("E:\\run\\test\\a.jpg")){//connect and log inftpClient.connect("192.168.254.181", 21);ftpClient.login("root", "root");ftpClient.changeWorkingDirectory("image");//Switch directory//download file//parameter 1: server specified file//Parameter 2: Local output stream (responsible for writing after downloading)ftpClient.setFileType(FTPClient.BINARY_FILE_TYPE);boolean isRetrieve = ftpClient.retrieveFile(downlaodFileName, download);System.out.println("Successful download?"+isRetrieve);} catch (SocketException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}finally {try {ftpClient.disconnect();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}