• 编码格式: UTF-8等;
• 文件类型： 包括[BINARY_FILE_TYPE(常用)]和[ASCII_FILE_TYPE]两种;
• 数据连接模式：一般使用LocalPassiveMode模式，因为大部分客户端都在防火墙后面；

              1. LocalPassiveMode：服务器端打开数据端口，进行数据传输；

              2. LocalActiveMode：客户端打开数据端口，进行数据传输；

• 系统类型：UNIX/WINDOWS等，默认为Unix

• 步骤1： 创建FTPClient对象，设置ftpClient属性：如编码格式、连接超时、文件上传下载进度监听器等;
• 步骤2： 使用ftpClient连接远程server：connect()；
• 步骤3： 获取connect()的返回码getReplyCode()，判断是否连接成功：isPositiveCompletion()；
• 步骤4： 登录远程server：login(),并转到相应目录，必要时要递归创建目录;
• 步骤5： 设置ftpClient属性：如缓存大小、文件类型、超时时间、数据连接模式等；
• 步骤6： ftp相关操作：如文件上传、下载等；
• 步骤7： 断开连接，释放资源：logout()/disconnect();

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package com.sssppp.Communication;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.RandomAccessFile;

import org.apache.commons.net.PrintCommandListener;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPClientConfig;
import org.apache.commons.net.ftp.FTPFile;
import org.apache.commons.net.ftp.FTPReply;
import org.apache.commons.net.io.CopyStreamEvent;
import org.apache.commons.net.io.CopyStreamListener;

/**
 * FTP进行文件上传和下载；
 * 支持断点续传；
 */
public final class FTPUtil {
  private final FTPClient ftp = new FTPClient();

  /**
   * 
   * @param hostname
   *            如：IP
   * @param port
   * @param username
   * @param password
   * @return
   * @throws IOException
   */
  public boolean connect(String hostname, int port, String username,
      String password) throws IOException {
    boolean debug = false;
    if (debug) {
      // 设置将过程中使用到的命令输出到控制台
      this.ftp.addProtocolCommandListener(new PrintCommandListener(
          new PrintWriter(System.out), true));
    }

    //设置系统类型
    final FTPClientConfig config = new FTPClientConfig(
        FTPClientConfig.SYST_UNIX);
    this.ftp.configure(config);

    try {
      this.ftp.connect(hostname, port);
      if (!FTPReply.isPositiveCompletion(this.ftp.getReplyCode())) {
        this.ftp.disconnect();
        System.err.println("FTP server refused connection.");
        return false;
      }
    } catch (IOException e) {
      if (this.ftp.isConnected()) {
        try {
          this.ftp.disconnect();
        } catch (IOException f) {
        }
      }
      System.err.println("Could not connect to server.");
      e.printStackTrace();
      return false;
    }

    if (!this.ftp.login(username, password)) {
      this.ftp.logout();
      System.err.println("Could not login to server.");
      return false;
    }

    return true;
  }
  
  public void disconnect() throws IOException {
    if (this.ftp.isConnected()) {
      try {
        this.ftp.logout();
        this.ftp.disconnect();
      } catch (IOException f) {
      }
    }
  }

  /**
   * 
   * @param absSrcFileName
   * @param destDir
   * @param destFileName
   * @throws IOException
   */
  public void upLoadByFtp(String absSrcFileName, String destDir,
      String destFileName) throws IOException {
    // 创建并转到工作目录
    String absDstDir = this.ftp.printWorkingDirectory() + "/" + destDir;
    absDstDir = absDstDir.replaceAll("//", "/");
    createDirectory(absDstDir, this.ftp);

    // 设置各种属性
    this.ftp.setFileType(FTP.BINARY_FILE_TYPE);
    // Use passive mode as default because most of us are behind firewalls these days.
    this.ftp.enterLocalPassiveMode();
    this.ftp.setControlEncoding("utf-8");
    this.ftp.setBufferSize(1024);

    // 进度监听
    File srcFile = new File(absSrcFileName);
    this.ftp.setCopyStreamListener(new MyCopyStreamListener(srcFile.length()));

    FTPFile[] files = this.ftp.listFiles(destFileName);
    if (files.length == 1) {// 断点续传
      long dstFileSize = files[0].getSize();
      if (srcFile.length() <= dstFileSize) {// 文件已存在
        return;
      }
      boolean b = uploadFile(destFileName, srcFile, this.ftp, dstFileSize);
      if (!b) {// 如果断点续传没有成功，则删除服务器上文件，重新上传
        if (this.ftp.deleteFile(destFileName)) {
          uploadFile(destFileName, srcFile, this.ftp, 0);
        }else {
          System.err.println("Delete file fail.");
        }
      }
    } else {
      uploadFile(destFileName, srcFile, this.ftp, 0);
    }
  }
  
  /**
   * 
   * @param remoteFileName
   * @param localFileName
   * @throws IOException
   */
  public void downLoadByFtp(String remoteFileName, String localFileName)
      throws IOException {
    InputStream input = null;
    FileOutputStream fos = null;

    // 设置各种属性
    this.ftp.setBufferSize(1024);
    this.ftp.setDataTimeout(1000 * 10);
    this.ftp.setFileType(FTPClient.BINARY_FILE_TYPE);
    this.ftp.enterLocalPassiveMode();
    
    // 判断远程文件是否存在
    FTPFile[] files = this.ftp.listFiles(remoteFileName);
    if (files.length != 1) {
      System.err.println("Remote file not exist.");
      return;
    }

    //进度监听
    long remoteSize = files[0].getSize();
    this.ftp.setCopyStreamListener(new MyCopyStreamListener(remoteSize));

    File file = new File(localFileName);
    if (file.exists()) {
      long localSize = file.length();
      if (localSize >= remoteSize) {
        return;
      }
      System.out.println("@@@Break point download.@@@");
      fos = new FileOutputStream(file, true);// append模式
      this.ftp.setRestartOffset(localSize);
    } else {
      fos = new FileOutputStream(file); // override模式
    }

    input = this.ftp.retrieveFileStream(remoteFileName);
    byte[] b = new byte[8192];
    int n = 0;
    while (-1 != (n = input.read(b))) {
      if (Thread.currentThread().isInterrupted()) {
        break;
      }
      fos.write(b, 0, n);
    }

    if (input != null) {
      input.close();
    }
    if (fos != null) {
      fos.flush();
      fos.close();
    }

    if (!this.ftp.completePendingCommand()) {
      System.err.println("Download file fail.");
      this.ftp.logout();
      this.ftp.disconnect();
    }
  }
  
  /**
   * 
   * @param destFileName
   * @param srcFile
   * @param ftpClient
   * @param dstFileSize 文件写入的起始位置； >0:表示断点续传，<=0:表示上传新文件
   * @return
   * @throws IOException
   */
  private boolean uploadFile(String destFileName, File srcFile,
      FTPClient ftpClient, long dstFileSize) throws IOException {
    RandomAccessFile input = null;
    OutputStream fout = null;
    
    input = new RandomAccessFile(srcFile, "r"); // 只读模式
    if (dstFileSize > 0) {// 断点续传
      fout = ftpClient.appendFileStream(destFileName);
      input.seek(dstFileSize);
      ftpClient.setRestartOffset(dstFileSize);
    } else {
      fout = ftpClient.storeFileStream(destFileName);
    }

    byte[] b = new byte[8192]; // 缓存大小
    int n = 0;
    while (-1 != (n = input.read(b))) {
      if (Thread.currentThread().isInterrupted()) {
        break;
      }
      fout.write(b, 0, n);
    }

    if (input != null) {
      input.close();
    }
    if (fout != null) {
      fout.flush();
      fout.close();
    }
    if (!ftpClient.completePendingCommand()) {
      System.err.println("Upload file fail.");
      ftpClient.logout();
      ftpClient.disconnect();
      return false;
    }
    return true;
  }

  /**
   * 在FTP服务器上创建并转到工作目录
   * 
   * @param relativePath
   *            相对工作路径，不包含文件名：如 dd/11/22/33
   * @param ftpClient
   *            录创建是否成功
   * @return
   * @throws IOException
   */
  private boolean createDirectory(String relativePath, FTPClient ftpClient)
      throws IOException {
    if (!relativePath.startsWith("/")) {
      relativePath = "/" + relativePath;
    }
    String dir = (ftpClient.printWorkingDirectory().equals("/") ? ""
        : ftpClient.printWorkingDirectory()) + relativePath;
    if (!ftpClient.changeWorkingDirectory(dir)) {
      //目录不存在，则创建各级目录
      for (String subDir : relativePath.split("/")) {
        if (!subDir.equals("")) {
          String newDir = ftpClient.printWorkingDirectory() + "/"
              + subDir;
          ftpClient.mkd(newDir);
          if (!ftpClient.changeWorkingDirectory(newDir)) {
            return false;
          }
        }
      }
    }
    return true;
  }

  
  /**
   * 进度监听器
   */
  private class MyCopyStreamListener implements CopyStreamListener {
    private long totalSize = 0;
    private long percent = -1; // 进度

    /**
     * 文件的总大小
     * @param totalSize
     */
    public MyCopyStreamListener(long totalSize) {
      super();
      this.totalSize = totalSize;
    }

    @Override
    public void bytesTransferred(CopyStreamEvent event) {
      bytesTransferred(event.getTotalBytesTransferred(),
          event.getBytesTransferred(), event.getStreamSize());
    }

    //totalBytesTransferred:当前总共已传输字节数;
    //bytesTransferred:最近一次传输字节数
    @Override
    public void bytesTransferred(long totalBytesTransferred,
        int bytesTransferred, long streamSize) {
      if (percent >= totalBytesTransferred * 100 / totalSize) {
        return;
      }
      percent = totalBytesTransferred * 100 / totalSize;

      System.out.println("Completed " + totalBytesTransferred + "("
          + percent + "%) out of " + totalSize + ".");
    }

  }

  public static void main(String[] args) throws IOException {
    String hostname = "10.180.137.241";
    String username = "xxx";
    String password = "xxx";
    int port = 21;
    
    FTPUtil ftp = new FTPUtil();
    
    //上传文件
    String absSrcFileName = "C:\\tmp\\m2eclipse1.zip";
    String destDir = "ww/11/22/33";
    String destFileName = "m2eclipse1.zip";
    ftp.connect(hostname, port, username, password);
    ftp.upLoadByFtp(absSrcFileName, destDir, destFileName);
    ftp.disconnect();

    // 下载文件
    String localFileName = "C:\\tmp\\m2eclipse-download3333.zip";
    String remoteFileName = "/ww/11/22/33/m2eclipse.zip";
    ftp.connect(hostname, port, username, password);
    ftp.downLoadByFtp(remoteFileName, localFileName);
    ftp.disconnect();
  }
}

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官方Demo： http://commons.apache.org/proper/commons-net/examples/ftp/FTPClientExample.java 

https://my.oschina.net/csmw00/blog/676049 （可参考如何实现进度监控）

http://yujie020.blog.51cto.com/2827685/655338