用Java构建稳定的Ftp服务器 (3)

pahdmbczpe

　　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.lastModified()));
if(files.isDirectory()) {
writer.println("drwxrwxrwx 1 ftp System 0 "
+ dateStr + " " + files.getName());
}
else {
writer.println("-rwxrwxrwx 1 ftp System "
+ getFileLength(files.length()) + " " + dateStr + " " + files.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();
}
　　（待续）