Java

Resume an Interrupted FTP Transfer

Demonstrates the RestartNext and PartialTransfer properties, which request that the next transfer resume from existing content and report whether a download was incomplete.

Note: The local paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: For a large transfer over a flaky link, restarting from zero after a drop is wasteful. Setting RestartNext makes the next download continue from the current local file size (and the next upload from the remote size); the flag is consumed by that one transfer and then reset. Afterward PartialTransfer tells you whether the download got only part of the file — the signal to set RestartNext again and resume once more.

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Chilkat2 Java

import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Ftp2;

public class ChilkatExample {

    public static void main(String[] args) {
        Ftp2 ftp = new Ftp2();

        ftp.setHostname("ftp.example.com");
        ftp.setUsername("myFtpLogin");

        // Normally you would not hard-code the password in source.  You should instead obtain it
        // from an interactive prompt, environment variable, or a secrets vault.
        ftp.setPassword("myPassword");

        try {
            ftp.connect();

            // RestartNext requests that the NEXT transfer resume from existing content rather than starting
            // over.  It is consumed by that transfer and then automatically reset.
            ftp.setRestartNext(true);

            // Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
            // the current local file size.
            ftp.getFile("public_html/bigfile.zip", "qa_output/bigfile.zip");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // PartialTransfer indicates whether the most recent download received some, but not all, of the
        // remote file -- distinguishing a mid-transfer failure from other outcomes.
        if (ftp.getPartialTransfer()) {
            System.out.println("Only part of the file was received; another resume may be needed.");
        } else {
            System.out.println("The file was fully received.");
        }

        try {
            ftp.disconnect();
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }
    }
}