ftp4j之FTP

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　　The ftp4j library implements a Java full-features FTP client. With ftp4j embedded in your application you can: transfer files (upload and download), browse the remote FTP site (directory listing included), create, delete, rename and move remote directories and files.
　　
　　ftp4j类库可支持实现java版的FTP客户端，可应用到你的应用程序中，实现文件的上传下载，浏览远程FTP服务器上的目录和文件，创建、删除、重命，移动远程目录和文件等操作。
　　
　　ftp4j的特点：
　　
　　1、100%免费
　　2、可远程连接FTP服务器
　　3、远程操作
　　4、文件上传下载
　　5、异常捕获
　　
　　下载路径：http://www.sauronsoftware.it/projects/ftp4j/ftp4j-1.3.1.zip
　　
　　快速上手：
　　
　　The main class of the library is FTPClient (it.sauronsoftware.ftp4j.FTPClient).
　　Start creating a FTPClient instance:

FTPClient client = new FTPClient();
　　Connect now to a remote FTP service:

client.connect("ftp.host.com");
　　If the service port is other than the standard 21:

client.connect("ftp.host.com", port);
　　In example:

client.connect("ftp.host.com", 8021);
　　Step now to the login procedure:

client.login("carlo", "mypassword");
　　If no exception is thrown you are now authenticated to the remote server. Otherwise, if the authentication attempt fails, you receive a it.sauronsoftware.ftp4j.FTPException.
　　Anonymous authentication, if admitted by the connected service, can be done sending the username "anonymous" and an arbitrary password (note that some servers require an e-mail address in place of the password):

client.login("anonymous", "ftp4j");
　　Do anything you want with the remote FTP service, then disconnect:

client.disconnect(true);
　　This one sends the FTP QUIT command to the remote server, requesting a legal disconnect procedure. If you just want to break the connection, without sending any advice to the server, call:

client.disconnect(false);
　　

Connecting through a proxy
　　The client connects to the server through a connector (an object implementing the it.sauronsoftware.ftp4j.FTPConnector interface), which returns to the client an already open connection (an object implementing the it.sauronsoftware.ftp4j.FTPConnection interface). That is why ftp4j could support a large set of proxies.
　　The connector for a client instance can be setted with the setConnector() method, obviously before connecting the remote server:

client.setConnector(anyConnectorYouWant);
Browsing the remote site
　　Get the current directory absolute path calling:

String dir = client.currentDirectory();
　　Change directory with:

client.changeDirectory(newPath);
　　You can use both absolute and relative paths:

client.changeDirectory("/an/absolute/one");
client.changeDirectory("relative");
　　Back to the parent directory with:

client.changeDirectoryUp();
　　

Renaming files and directories
　　To rename a remote file or directory:

client.rename("oldname", "newname");
　　

Moving files and directories
　　The rename() method can also be used to move files and directories from a location to another.
　　In example, think in the current working directory you have a file called "myfile.txt", and you want to move it in the sub-directory "myfolder":

client.rename("myfile.txt", "myfolder/myfile.txt");
　　

Deleting files
　　To delete a remote file call:

client.deleteFile(relativeOrAbsolutePath);
　　In example:

client.deleteFile("useless.txt");
　　

Creating and deleting directories
　　You can create a new directory on the remote site, if the service gives you this oppurtunity:

client.createDirectory("newfolder");
　　You can also remove an existing one:

client.deleteDirectory(absoluteOrRelativePath);
　　In example:

client.deleteDirectory("oldfolder");
　　Please note that usually FTP servers can delete only empty directories.
　　
　　

Downloading and uploading files
　　The easiest way to download a remote file is a call to the download(String, File) method:

client.download("remoteFile.ext", new java.io.File("localFile.ext"));
　　To upload:

client.upload(new java.io.File("localFile.ext"));
　　
　　
　　参考文章路径:http://www.sauronsoftware.it/projects/ftp4j/manual.php#3