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The problem

The sftp protocol is not supported by default by java.net.URL, you will run into a MalformedURLException. The ftp protocol is (still) supported in some Java versions but that is obsolete.

The goal of this package is to allow you to change your application (configuration) from ftp://username:password@host/path/file to sftp://username:password@host/path/file or to use certificate authentication instead of a password: sftp://username@host/path/file

sftp is supported by the Jsch library but you cannot do sftp via URLs, which "blocks" any existing code that used ftp:// URLs and grabbed input and output streams, without caring how the protocol is actually implemented.

Jsch is also not so easy to work with, and a few of its issues (like "channel was closed") affect apache vsf2 hence (my) attempts to implement a reliable sftp URL handler using vfs2 failed.

It is also hard to plug in new URL stream handler factories in a servlet container like Tomcat. The JVM does not allow adding multiple such factories, and tomcat already defines one. Even if tomcat allows plugging in more, there are more complications, as Jsch starts a thread for each SFTP session, and new threads are not trivial to manage in reloadable web apps, as the original classloader is lost.

Solution

To support sftp:// URL connections for both InputStreams and OutputStreams in your JVM:

  java.net.URL.setURLStreamHandlerFactory(new org.makumba.SftpURLStreamHandlerFactory())

Tomcat use

If you are in a Tomcat servlet/JSP environment, use a TomcatSftpURLInstaller to plug in this sftp URL handlder factory in the Tomcat JVM. It can be configured:

  • in conf/server.xml inside an <Engine> tag
  • in your webapp configuration META-INF/context.xml inside a <Context > tag.
<Listener className="org.makumba.TomcatSftpURLInstaller" />

In both cases, it is recommended that the JAR dependencies (this package: sftp-url.jar and jsch-0.2.x.jar) are placed in the tomcat lib/ folder beacause most Jsch objects are hanged in a thread (one for each SFTP Session) and, in case of webapp reload, that thread will lose the classes for the objects that it works with. Using a servlet context listener to stop that thread did not yield good results, but you may want to contribute a solution. That would allow deployment on tomcats where the lib/ folder is not accessible.