FTP connection through proxy with Java
Properties props = System.getProperties();
props.put("ftp.proxySet", "true");
// dummy details
props.put("ftp.proxyHost", "proxy.example.server");
props.put("ftp.proxyPort", "8080");

conn = url.openConnection();
String password = "username:password";
String encodedPassword = new String(Base64.encodeBase64(password.getBytes()));
conn.setRequestProperty("Proxy-Authorization", encodedPassword);

private static class MyAuthenticator extends Authenticator {
    private String username;
    private String password;
    public MyAuthenticator(String username, String password) {
        super();
        this.username = username;
        this.password = password;
    }
    @Override
    protected PasswordAuthentication getPasswordAuthentication() {
        return new PasswordAuthentication(username, password.toCharArray());
    }
}

public static void main(String[] args) {
    Authenticator.setDefault(new MyAuthenticator("foo", "bar"));
    System.setProperty("...", "...");
}