The small-file size was 1 Kb, and the number of small files, 10,000. As a consequence, the large-file size was 10 Mb. The experimental settings were set as follows: The transfer data volume was 10 Mb. Also, to smooth any incidents, I took 10 versions of the measures and calculated the median average. To keep the measures clean, any external transfer on the network segment was excluded during the measures. The transfer occurred between two similar machines connected by a TCP/IP network. The files' numbers and sizes were designed to measure the same data volumes. The large and small files were used to measure the large-file and small-file transfer speeds, respectively. The experimental protocol used to obtain these measures was conducted as follows: One large file and many small files were created on the FTP server. For example, a library for video transfer over a network should score high at transferring large files, whereas a library for an application that involves many interactions with the FTP server should score high at transferring many small files. These two measures should help in selecting which library is best suited for the target application's specific needs. The second measures the transfer speed of many small files and indicates how fast the library operates the communication protocol with the server.
The first measure represents the transfer speed of one large file and indicates how fast the library transfers data over a network. The libraries' performance comparison is based on two measures of transfer speeds. This comparison identifies what kinds of SFTP and FTPS secure FTP transfers are supported by each library. Although the protocols have similar names and functions, they are completely different. This kind of implementation is referred to as SFTP. FTP security can also be implemented as a subprotocol of SSH (Secure Shell). Both implicit SSL and explicit SSL are typically referred to as FTPS (FTP over SSL). Explicit secure FTP is FTP over SSL, but instead of using a direct SSL connection as in implicit connection, it first connects to the server using a plain-text FTP connection and then switches to SSL mode using the AUTH SSL or AUTH TLS command to switch to a secure SSL connection. Implicit secure FTP is actually FTP over Secure Socket Layer, using a direct SSL connection, typically over port 990. According to the recommendation, secure FTP extensions can be of two types: implicit and explicit. The security extensions for FTP are defined in the Internet Engineering Task Force's reference document RFC2228. The performance criterion compares the libraries' transfer speeds. The security support criterion indicates whether the library implements the security extensions for FTP. New criteria for this evaluation are security support and file transfer performance. I covered some of this criteria in " Java FTP Client Libraries Reviewed"-please refer to that article for a review. The comparison involves a number of criteria, including features supported, commercial aspects with regard to the library provider, and file transfer performance. To help decision-makers choose a library that suits their needs, this article compares and evaluates these libraries. Therefore, selecting the right library with regard to specific needs can prove difficult.
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Indeed, all these libraries implement different features, at various prices, with diverse levels of quality and license terms. This list is quite long, and comparing the libraries is not straightforward. Enterprise Distributed Technologies' FTPj.Many Java FTP libraries exist and are available on the Internet. To get complete RFC959-compliant support and convenient methods, Java developers must turn to the third-party libraries available on the market. In addition, when using the JDK's FTP support, FTP server responses are returned as raw strings instead of convenient Java objects. Thus, when RFC959-compliance is needed, the JDK proves unsatisfying. For example, the JDK does not allow the creation of directories on the server or permit the FTP connection to remain open between two file transfers. As discussed in my previous JavaWorld article " Java FTP Client Libraries Reviewed" (April 2003), FTP support in the JDK does not fully implement the FTP specification (Request for Comments 959).
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