Programming Design Notes

在 Java 使用 FTP 去上載檔案，下載檔案或去做其他操作也是很簡單，因為 Java API 已經包括了對 FTP 的支援。如果不是使用 FTP，而是使用 SFTP: SSH File Transfer Protocol，使用Java API 實作便有點麻煩了。

幸好 Apache Commons VFS 替我們實作了 SFTP 的操作，Apache Commons VFS 配合 JSch 使我們可以很簡單地使用 SSH 連接 Server 和上載檔案，下載檔案等等操作。

廢話不多說，首先要準備 3 個 Library:

• Apache Commons VFS - http://commons.apache.org/vfs/download_vfs.cgi
  
• Apache Commons Logging - http://commons.apache.org/logging/download_logging.cgi
• JSch - http://www.jcraft.com/jsch/

下載好後將 .jar 加到 class path 令程式找到這些 Library。

再來就是寫程式，為了方便好看，我會將所有程式碼放到 Main class 內。

第一步是製作一個 Function 去將 Protocol，Host Name，Username，Password 和 Server 上的檔案位置連接起來 (Factory Method)。令到 Apache Commons VFS 能讀得懂。

public static String createConnectionString(String hostName,
        String username, String password, String remoteFilePath) {
    // result: "sftp://user:[email protected]/resume.pdf
    return "sftp://" + username + ":" + password + "@" + hostName + "/"
            + remoteFilePath;
}

第二步是製作一個 Function 去製造出一個 SFTP 預設的設定 (Factory Method):

public static FileSystemOptions createDefaultOptions()
        throws FileSystemException {
    // Create SFTP options
    FileSystemOptions opts = new FileSystemOptions();

    // SSH Key checking
    SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(
            opts, "no");

    // Root directory set to user home
    SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, true);

    // Timeout is count by Milliseconds
    SftpFileSystemConfigBuilder.getInstance().setTimeout(opts, 10000);

    return opts;
}

第三步是製作一個上載檔案的 Function:

public static void upload(String hostName, String username,
        String password, String localFilePath, String remoteFilePath) {

    File f = new File(localFilePath);
    if (!f.exists())
        throw new RuntimeException("Error. Local file not found");

    StandardFileSystemManager manager = new StandardFileSystemManager();

    try {
        manager.init();

        // Create local file object
        FileObject localFile = manager.resolveFile(f.getAbsolutePath());

        // Create remote file object
        FileObject remoteFile = manager.resolveFile(
                createConnectionString(hostName, username, password,
                        remoteFilePath), createDefaultOptions());

        // Copy local file to sftp server
        remoteFile.copyFrom(localFile, Selectors.SELECT_SELF);

        System.out.println("File upload success");
    } catch (Exception e) {
        throw new RuntimeException(e);
    } finally {
        manager.close();
    }
}

在這裡可以測試一下上載檔案的 Function 是否沒有問題:

/*
 * args[0]: hostName 
 * args[1]: username 
 * args[2]: password 
 * args[3]:localFilePath 
 * args[4]: remoteFilePath
 */
public static void main(String[] args) {
    if (args.length < 5)
        throw new RuntimeException(
                "Error. Please enter "
                        + "args[0]: hostName, args[1]: username, args[2]: password, "
                        + "args[3]: localFilePath, args[4]: remoteFilePath.");

    upload(args[0], args[1], args[2], args[3], args[4]);
}

成功後 Console 會打印出 File upload success。

再來是加下載檔案的 Function:

public static void download(String hostName, String username,
        String password, String localFilePath, String remoteFilePath) {

    StandardFileSystemManager manager = new StandardFileSystemManager();

    try {
        manager.init();

        String downloadFilePath = localFilePath.substring(0,
                localFilePath.lastIndexOf("."))
                + "_downlaod_from_sftp"
                + localFilePath.substring(localFilePath.lastIndexOf("."),
                        localFilePath.length());

        // Create local file object
        FileObject localFile = manager.resolveFile(downloadFilePath);

        // Create remote file object
        FileObject remoteFile = manager.resolveFile(
                createConnectionString(hostName, username, password,
                        remoteFilePath), createDefaultOptions());

        // Copy local file to sftp server
        localFile.copyFrom(remoteFile, Selectors.SELECT_SELF);

        System.out.println("File download success");
    } catch (Exception e) {
        throw new RuntimeException(e);
    } finally {
        manager.close();
    }
}

測試檔案是否存在的 Function:

public static boolean exist(String hostName, String username,
        String password, String remoteFilePath) {
    StandardFileSystemManager manager = new StandardFileSystemManager();

    try {
        manager.init();

        // Create remote object
        FileObject remoteFile = manager.resolveFile(
                createConnectionString(hostName, username, password,
                        remoteFilePath), createDefaultOptions());

        System.out.println("File exist: " + remoteFile.exists());

        return remoteFile.exists();
    } catch (Exception e) {
        throw new RuntimeException(e);
    } finally {
        manager.close();
    }
}

刪除 Server 檔案的 Function:

public static void delete(String hostName, String username,
        String password, String remoteFilePath) {
    StandardFileSystemManager manager = new StandardFileSystemManager();

    try {
        manager.init();

        // Create remote object
        FileObject remoteFile = manager.resolveFile(
                createConnectionString(hostName, username, password,
                        remoteFilePath), createDefaultOptions());

        if (remoteFile.exists()) {
            remoteFile.delete();
            System.out.println("Delete remote file success");
        }
    } catch (Exception e) {
        throw new RuntimeException(e);
    } finally {
        manager.close();
    }
}

完整的程式:

package sftp.sample;

import java.io.File;

import org.apache.commons.vfs.FileObject;
import org.apache.commons.vfs.FileSystemException;
import org.apache.commons.vfs.FileSystemOptions;
import org.apache.commons.vfs.Selectors;
import org.apache.commons.vfs.impl.StandardFileSystemManager;
import org.apache.commons.vfs.provider.sftp.SftpFileSystemConfigBuilder;

public class Main {

    /*
     * args[0]: hostName 
     * args[1]: username 
     * args[2]: password
     * args[3]: localFilePath 
     * args[4]: remoteFilePath
     */
    public static void main(String[] args) {
        if (args.length < 5)
            throw new RuntimeException(
                    "Error. Please enter "
                            + "args[0]: hostName, args[1]: username, args[2]: password, "
                            + "args[3]: localFilePath, args[4]: remoteFilePath.");

        upload(args[0], args[1], args[2], args[3], args[4]);
        exist(args[0], args[1], args[2], args[4]);
        download(args[0], args[1], args[2], args[3], args[4]);
        delete(args[0], args[1], args[2], args[4]);
    }

    public static void upload(String hostName, String username,
            String password, String localFilePath, String remoteFilePath) {

        File f = new File(localFilePath);
        if (!f.exists())
            throw new RuntimeException("Error. Local file not found");

        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {
            manager.init();

            // Create local file object
            FileObject localFile = manager.resolveFile(f.getAbsolutePath());

            // Create remote file object
            FileObject remoteFile = manager.resolveFile(
                    createConnectionString(hostName, username, password,
                            remoteFilePath), createDefaultOptions());

            // Copy local file to sftp server
            remoteFile.copyFrom(localFile, Selectors.SELECT_SELF);

            System.out.println("File upload success");
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            manager.close();
        }
    }

    public static void download(String hostName, String username,
            String password, String localFilePath, String remoteFilePath) {

        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {
            manager.init();

            String downloadFilePath = localFilePath.substring(0,
                    localFilePath.lastIndexOf("."))
                    + "_downlaod_from_sftp"
                    + localFilePath.substring(localFilePath.lastIndexOf("."),
                            localFilePath.length());

            // Create local file object
            FileObject localFile = manager.resolveFile(downloadFilePath);

            // Create remote file object
            FileObject remoteFile = manager.resolveFile(
                    createConnectionString(hostName, username, password,
                            remoteFilePath), createDefaultOptions());

            // Copy local file to sftp server
            localFile.copyFrom(remoteFile, Selectors.SELECT_SELF);

            System.out.println("File download success");
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            manager.close();
        }
    }

    public static void delete(String hostName, String username,
            String password, String remoteFilePath) {
        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {
            manager.init();

            // Create remote object
            FileObject remoteFile = manager.resolveFile(
                    createConnectionString(hostName, username, password,
                            remoteFilePath), createDefaultOptions());

            if (remoteFile.exists()) {
                remoteFile.delete();
                System.out.println("Delete remote file success");
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            manager.close();
        }
    }

    public static boolean exist(String hostName, String username,
            String password, String remoteFilePath) {
        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {
            manager.init();

            // Create remote object
            FileObject remoteFile = manager.resolveFile(
                    createConnectionString(hostName, username, password,
                            remoteFilePath), createDefaultOptions());

            System.out.println("File exist: " + remoteFile.exists());

            return remoteFile.exists();
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            manager.close();
        }
    }

    public static String createConnectionString(String hostName,
            String username, String password, String remoteFilePath) {
        // result: "sftp://user:[email protected]/resume.pdf
        return "sftp://" + username + ":" + password + "@" + hostName + "/"
                + remoteFilePath;
    }

    public static FileSystemOptions createDefaultOptions()
            throws FileSystemException {
        // Create SFTP options
        FileSystemOptions opts = new FileSystemOptions();

        // SSH Key checking
        SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(
                opts, "no");

        // Root directory set to user home
        SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, true);

        // Timeout is count by Milliseconds
        SftpFileSystemConfigBuilder.getInstance().setTimeout(opts, 10000);

        return opts;
    }

}

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