Java构建FTP服务器

我会带着你远行 2022-08-03 13:50 186阅读 0赞

[Java构建Ftp服务器程序段][Java_Ftp]

下面我们要处理用户连接，也就是FtpConnection类。Ftp连接本质上是一个状态机，当FtpConnection接收到用户命令后，根据当前状态决定响应及下一个状态。不过我们不需要考虑实现一个复杂的状态机，只须监听/接收/处理/响应即可：

package jftp;  
  
import java.net.\*;  
import java.io.\*;  
import java.util.\*;  
import java.text.\*;  
  
public class FtpConnection extends Thread \{  
/\*\* 主目录 \*/  
static public String root = null;  
private String currentDir = "/"; // 当前目录  
private Socket socket;  
private BufferedReader reader = null;  
private BufferedWriter writer = null;  
private String clientIP = null;  
private Socket tempSocket = null; // tempSocket用于传送文件  
private ServerSocket pasvSocket = null; // 用于被动模式  
private String host = null;  
private int port = (-1);  
  
public FtpConnection(Socket socket) \{  
this.socket = socket;  
this.clientIP = socket.getInetAddress().getHostAddress();  
\}  
  
public void run() \{  
String command;  
try \{  
System.out.println(clientIP + " connected.");  
socket.setSoTimeout(60000); // ftp超时设定  
reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));  
writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));  
response("220-欢迎消息......");  
response("220-欢迎消息......");  
response("220 注意最后一行欢迎消息没有“-”");  
for(;;) \{  
command = reader.readLine();  
if(command == null)  
break;  
System.out.println("command from " + clientIP + " : " + command);  
parseCommand(command);  
if(command.equals("QUIT")) // 收到QUIT命令  
break;  
\}  
\}  
catch(Exception e) \{ e.printStackTrace(); \}  
finally \{  
try \{  
if(reader!=null) reader.close();  
\}catch(Exception e) \{\}  
try \{  
if(writer!=null) writer.close();  
\}catch(Exception e) \{\}  
try \{  
if(this.pasvSocket!=null) pasvSocket.close();  
\}catch(Exception e) \{\}  
try \{  
if(this.tempSocket!=null) tempSocket.close();  
\}catch(Exception e) \{\}  
try \{  
if(this.socket!=null) socket.close();  
\}catch(Exception e) \{\}  
\}  
System.out.println(clientIP + " disconnected.");  
 \}  
\}

FtpConnection在run()方法中仅仅是获得用户命令/处理命令，当收到QUIT时，关闭连接，结束Ftp会话。

先准备几个辅助方法：

private void response(String s) throws Exception \{  
// System.out.println(" \[RESPONSE\] "+s);  
writer.write(s);  
writer.newLine();  
writer.flush(); // 注意要flush否则响应仍在缓冲区  
\}  
  
// 生成一个字符串  
private static String pad(int length) \{  
StringBuffer buf = new StringBuffer();  
for (int i = 0; i < length; i++)  
buf.append((char)' ');  
return buf.toString();  
\}  
  
// 获取参数  
private String getParam(String cmd, String start) \{  
String s = cmd.substring(start.length(), cmd.length());  
return s.trim();  
\}  
  
// 获取路径  
private String translatePath(String path) \{  
if(path==null) return root;  
if(path.equals("")) return root;  
path = path.replace('/', '\\\\');  
return root + path;  
\}  
  
// 获取文件长度，注意是一个字符串  
private String getFileLength(long length) \{  
String s = Long.toString(length);  
int spaces = 12 - s.length();  
for(int i=0; i<spaces; i++)  
s = " " + s;  
return s;  
\}

接下来便是处理用户命令，这个方法有点长，需要重构一下，我只是把LIST命令单独挪了出来：

private void parseCommand(String s) throws Exception \{  
if(s==null || s.equals(""))  
return;  
if(s.startsWith("USER ")) \{  
response("331 need password");  
\}  
else if(s.startsWith("PASS ")) \{  
response("230 welcome to my ftp!");  
\}  
else if(s.equals("QUIT")) \{  
response("221 欢迎再来！");  
\}  
else if(s.equals("TYPE A")) \{  
response("200 TYPE set to A.");  
\}  
else if(s.equals("TYPE I")) \{  
response("200 TYPE set to I.");  
\}  
else if(s.equals("NOOP")) \{  
response("200 NOOP OK.");  
\}  
else if(s.startsWith("CWD")) \{ // 设置当前目录，注意没有检查目录是否有效  
this.currentDir = getParam(s, "CWD ");  
response("250 CWD command successful.");  
\}  
else if(s.equals("PWD")) \{ // 打印当前目录  
response("257 \\"" + this.currentDir + "\\" is current directory.");  
\}  
else if(s.startsWith("PORT ")) \{  
// 记录端口  
String\[\] params = getParam(s, "PORT ").split(",");  
if(params.length<=4 || params.length>=7)  
response("500 command param error.");  
else \{  
this.host = params\[0\] + "." + params\[1\] + "." + params\[2\] + "." + params\[3\];  
String port1 = null;  
String port2 = null;  
if(params.length == 6) \{  
port1 = params\[4\];  
port2 = params\[5\];  
\}  
else \{  
port1 = "0";  
port2 = params\[4\];  
\}  
this.port = Integer.parseInt(port1) \* 256 + Integer.parseInt(port2);  
response("200 command successful.");  
\}  
\}  
else if(s.equals("PASV")) \{ // 进入被动模式  
if(pasvSocket!=null)  
pasvSocket.close();  
try \{  
pasvSocket = new ServerSocket(0);  
 int pPort = pasvSocket.getLocalPort();  
String s\_port;  
if(pPort<=255)  
s\_port = "255";  
else \{  
int p1 = pPort / 256;  
int p2 = pPort - p1\*256;  
s\_port = p1 + "," + p2;  
\}  
pasvSocket.setSoTimeout(60000);  
response("227 Entering Passive Mode ("  
\+ InetAddress.getLocalHost().getHostAddress().replace('.', ',')  
\+ "," + s\_port + ")");  
\}  
catch(Exception e) \{  
if(pasvSocket!=null) \{  
pasvSocket.close();  
pasvSocket = null;  
\}  
\}  
\}  
else if(s.startsWith("RETR")) \{ // 传文件  
String file = currentDir + (currentDir.endsWith("/") ? "" : "/") + getParam(s, "RETR");  
System.out.println("download file: " + file);  
Socket dataSocket;  
// 根据上一次的PASV或PORT命令决定使用哪个socket  
if(pasvSocket!=null)  
dataSocket = pasvSocket.accept();  
else  
dataSocket = new Socket(this.host, this.port);  
 OutputStream dos = null;  
InputStream fis = null;  
response("150 Opening ASCII mode data connection.");  
 try \{  
fis = new BufferedInputStream(new FileInputStream(translatePath(file)));  
dos = new DataOutputStream(new BufferedOutputStream(dataSocket.getOutputStream()));  
 // 开始正式发送数据:  
byte\[\] buffer = new byte\[20480\]; // 发送缓冲 20k  
 int num = 0; // 发送一次读取的字节数  
do \{  
num = fis.read(buffer);  
if(num!=(-1)) \{  
// 发送：  
dos.write(buffer, 0, num);  
dos.flush();  
\}  
\} while(num!=(-1));  
fis.close();  
fis = null;  
dos.close();  
dos = null;  
dataSocket.close();  
dataSocket = null;  
response("226 transfer complete."); // 响应一个成功标志  
\}  
catch(Exception e) \{  
response("550 ERROR: File not found or access denied.");  
\}  
finally \{  
try \{  
if(fis!=null) fis.close();  
if(dos!=null) dos.close();  
if(dataSocket!=null) dataSocket.close();  
\}  
catch(Exception e) \{\}  
\}  
\}  
 else if(s.equals("LIST")) \{ // 列当前目录文件  
Socket dataSocket;  
// 根据上一次的PASV或PORT命令决定使用哪个socket  
if(pasvSocket!=null)  
dataSocket = pasvSocket.accept();  
else  
dataSocket = new Socket(this.host, this.port);  
PrintWriter writer = new PrintWriter(new BufferedOutputStream(dataSocket.getOutputStream()));  
response("150 Opening ASCII mode data connection.");  
 try \{  
responseList(writer, this.currentDir);  
writer.close();  
dataSocket.close();  
response("226 transfer complete.");  
\}  
catch(IOException e) \{  
writer.close();  
dataSocket.close();  
response(e.getMessage());  
\}  
dataSocket = null;  
\}  
else \{  
response("500 invalid command"); // 没有匹配的命令，输出错误信息  
\}  
\}  
  
// 响应LIST命令  
private void responseList(PrintWriter writer, String path) throws IOException \{  
File dir = new File(translatePath(path));  
if(!dir.isDirectory())  
throw new IOException("550 No such file or directory");  
 File\[\] files = dir.listFiles();  
String dateStr;  
for(int i=0; i<files.length; i++)="" \{  
dateStr = new SimpleDateFormat("MMM dd hh:mm").format(new Date(files\[i\].lastModified()));  
if(files\[i\].isDirectory()) \{  
writer.println("drwxrwxrwx 1 ftp System 0 "  
\+ dateStr + " " + files\[i\].getName());  
\}  
else \{  
writer.println("-rwxrwxrwx 1 ftp System "  
\+ getFileLength(files\[i\].length()) + " " + dateStr + " " + files\[i\].getName());  
\}  
\}  
  
String file\_header = "-rwxrwxrwx 1 ftp System 0 Aug 5 19:59 ";  
String dir\_header = "drwxrwxrwx 1 ftp System 0 Aug 15 19:59 ";  
 writer.println("total " + files.length);  
writer.flush();  
\}

基本上我们的Ftp已经可以运行了，注意到我们在FtpConnection中处理USER和PASS命令，直接返回200 OK，如果需要验证用户名和口令，还需要添加相应的代码。

如何调试Ftp服务器？

有个最简单的方法，便是使用现成的Ftp客户端，推荐**[CuteFtp][]**，因为它总是把客户端发送的命令和服务器响应打印出来，我们可以非常方便的看到服务器的输出结果。

另外一个小Bug，文件列表在CuteFtp中可以正常显示，在其他Ftp客户端不一定能正常显示，这说明输出响应的“兼容性”还不够好，有空了看看Ftp的RFC再改进！**:**）

[Java_Ftp]: http://blog.chinaunix.net/uid-12613592-id-2926026.html
[CuteFtp]: http://www.cuteftp.com/