Question

如何用Java实现FTP服务器

Answer 1

FTP(File Transfer Protocol 文件传输协议)是Internet 上用来传送文件的协议。在Internet上通过FTP 服务器可以进行文件的上传(Upload)或下载(Download)。FTP是实时联机服务，在使用它之前必须是具有该服务的一个用户(用户名和口令)，工作时客户端必须先登录到作为服务器一方的计算机上，用户登录后可以进行文件搜索和文件传送等有关操作，如改变当前工作目录、列文件目录、设置传输参数及传送文件等。使用FTP可以传送所有类型的文件，如文本文件、二进制可执行文件、图象文件、声音文件和数据压缩文件等。
FTP 命令
FTP 的主要操作都是基于各种命令基础之上的。常用的命令有：
设置传输模式，它包括ASCⅡ(文本) 和BINARY 二进制模式;
目录操作，改变或显示远程计算机的当前目录(cd、dir/ls 命令);
连接操作，open命令用于建立同远程计算机的连接；close命令用于关闭连接;
发送操作，put命令用于传送文件到远程计算机；mput 命令用于传送多个文件到远程计算机;
获取操作，get命令用于接收一个文件；mget命令用于接收多个文件。
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import java.net.Socket;import org.apache.log4j.Logger;/** * 角色——服务器A * @author Leon * */public class ServerA{ public static void main(String[] args){ final String F_DIR = "c:/test";//根路径 final int PORT = 22;//监听端口号 Logger.getRootLogger(); Logger logger = Logger.getLogger("com"); try{ ServerSocket s = new ServerSocket(PORT); logger.info("Connecting to server A..."); logger.info("Connected Successful! Local Port:"+s.getLocalPort()+". Default Directory:'"+F_DIR+"'."); while( true ){ //接受客户端请求 Socket client = s.accept(); //创建服务线程 new ClientThread(client, F_DIR).start(); } } catch(Exception e) { logger.error(e.getMessage()); for(StackTraceElement ste : e.getStackTrace()){ logger.error(ste.toString()); } } }}import java.io.BufferedReader; import java.io.File;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.OutputStream;import java.io.PrintWriter;import java.io.RandomAccessFile;import java.net.ConnectException;import java.net.InetAddress;import java.net.ServerSocket;import java.net.Socket;import java.net.UnknownHostException;import java.nio.charset.Charset;import java.util.Random;import org.apache.log4j.Logger;/** * 客户端子线程类 * @author Leon * */public class ClientThread extends Thread { private Socket socketClient;//客户端socket private Logger logger;//日志对象 private String dir;//绝对路径 private String pdir = "/";//相对路径 private final static Random generator = new Random();//随机数 public ClientThread(Socket client, String F_DIR){ this.socketClient = client; this.dir = F_DIR; } @Override public void run() { Logger.getRootLogger(); logger = Logger.getLogger("com"); InputStream is = null; OutputStream os = null; try { is = socketClient.getInputStream(); os = socketClient.getOutputStream(); } catch (IOException e) { logger.error(e.getMessage()); for(StackTraceElement ste : e.getStackTrace()){ logger.error(ste.toString()); } } BufferedReader br = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8"))); PrintWriter pw = new PrintWriter(os); String clientIp = socketClient.getInetAddress().toString().substring(1);//记录客户端IP String username = "not logged in";//用户名 String password = "";//口令 String command = "";//命令 boolean loginStuts = false;//登录状态 final String LOGIN_WARNING = "530 Please log in with USER and PASS first."; String str = "";//命令内容字符串 int port_high = 0; int port_low = 0; String retr_ip = "";//接收文件的IP地址 Socket tempsocket = null; //打印欢迎信息 pw.println("220-FTP Server A version 1.0 written by Leon Guo"); pw.flush(); logger.info("("+username+") ("+clientIp+")> Connected, sending welcome message..."); logger.info("("+username+") ("+clientIp+")> 220-FTP Server A version 1.0 written by Leon Guo"); boolean b = true; while ( b ){ try { //获取用户输入的命令 command = br.readLine(); if(null == command) break; } catch (IOException e) { pw.println("331 Failed to get command"); pw.flush(); logger.info("("+username+") ("+clientIp+")> 331 Failed to get command"); logger.error(e.getMessage()); for(StackTraceElement ste : e.getStackTrace()){ logger.error(ste.toString()); } b = false; } /* * 访问控制命令 */ // USER命令 if(command.toUpperCase().startsWith("USER")){ logger.info("(not logged in) ("+clientIp+")> "+command); username = command.substring(4).trim(); if("".equals(username)){ pw.println("501 Syntax error"); pw.flush(); logger.info("(not logged in) ("+clientIp+")> 501 Syntax error"); username = "not logged in"; } else{ pw.println("331 Password required for " + username); pw.flush(); logger.info("(not logged in) ("+clientIp+")> 331 Password required for " + username); } loginStuts = false; } //end USER // PASS命令 else if(command.toUpperCase().startsWith("PASS")){ logger.info("(not logged in) ("+clientIp+")> "+command); password = command.substring(4).trim(); if(username.equals("root") && password.equals("root")){ pw.println("230 Logged on"); pw.flush(); logger.info("("+username+") ("+clientIp+")> 230 Logged on");// logger.info("客户端 "+clientIp+" 通过 "+username+"用户登录"); loginStuts = true; } else{ pw.println("530 Login or password incorrect!"); pw.flush(); logger.info("(not logged in) ("+clientIp+")> 530 Login or password incorrect!"); username = "not logged in"; } } //end PASS // PWD命令 else if(command.toUpperCase().startsWith("PWD")){ logger.info("("+username+") ("+clientIp+")> "+command); if(loginStuts){// logger.info("用户"+clientIp+"："+username+"执行PWD命令"); pw.println("257 /""+pdir+"/" is current directory"); pw.flush(); logger.info("("+username+") ("+clientIp+")> 257 /""+pdir+"/" is current directory"); } else{ pw.println(LOGIN_WARNING); pw.flush(); logger.info("("+username+") ("+clientIp+")> "+LOGIN_WARNING); } } //end PWD // CWD命令 else if(command.toUpperCase().startsWith("CWD")){ logger.info("("+username+") ("+clientIp+")> "+command); if(loginStuts){ str = command.substring(3).trim(); if("".equals(str)){ pw.println("250 Broken client detected, missing argument to CWD. /""+pdir+"/" is current directory."); pw.flush(); logger.info("("+username+") ("+clientIp+")> 250 Broken client detected, missing argument to CWD. /""+pdir+"/" is current directory."); } else{ //判断目录是否存在 String tmpDir = dir + "/" + str; File file = new File(tmpDir); if(file.exists()){//目录存在 dir = dir + "/" + str; if("/".equals(pdir)){ pdir = pdir + str; } else{ pdir = pdir + "/" + str; }// logger.info("用户"+clientIp+"："+username+"执行CWD命令"); pw.println("250 CWD successful. /""+pdir+"/" is current directory"); pw.flush(); logger.info("("+username+") ("+clientIp+")> 250 CWD successful. /""+pdir+"/" is current directory"); } else{//目录不存在 pw.println("550 CWD failed. /""+pdir+"/": directory not found."); pw.flush(); logger.info("("+username+") ("+clientIp+")> 550 CWD failed. /""+pdir+"/": directory not found.");

Answer 2

在主函数中，完成服务器端口的侦听和服务线程的创建。我们利用一个静态字符串变量initDir 来保存服务器线程运行时所在的工作目录。服务器的初始工作目录是由程序运行时用户输入的，缺省为C盘的根目录。
具体的代码如下：
public class ftpServer extends Thread{
private Socket socketClient;
private int counter;
private static String initDir;
public static void main(String[] args){
if(args.length != 0) {
initDir = args[0];
}else{ initDir = "c:";}
int i = 1;
try{
System.out.println("ftp server started!");
//监听21号端口
ServerSocket s = new ServerSocket(21);
for(;;){
//接受客户端请求
Socket incoming = s.accept();
//创建服务线程
new ftpServer(incoming,i).start();
i++;
}
}catch(Exception e){}
}