This post originated from an RSS feed registered with Java Buzz by Elliotte Rusty Harold. Original Post: Could not load a dependent class com/jcraft/jsch/Logger Feed Title: The Cafes Feed URL: http://cafe.elharo.com/feed/atom/? Feed Description: Longer than a blog; shorter than a book Latest Java Buzz Posts Latest Java Buzz Posts by Elliotte Rusty Harold Latest Posts From The Cafes

Have you ever seen an Ant error message like this?

BUILD FAILED
/Users/elharo/Projects/XOM/build.xml:545: Problem: failed to create task or type scp
Cause: Could not load a dependent class com/jcraft/jsch/Logger
       It is not enough to have Ant's optional JARs
       you need the JAR files that the optional tasks depend upon.
       Ant's optional task dependencies are listed in the manual.
Action: Determine what extra JAR files are needed, and place them in one of:
        -/opt/ant/lib
        -/Users/elharo/.ant/lib
        -a directory added on the command line with the -lib argument

Do not panic, this is a common problem.
The commonest cause is a missing JAR.

This is not a bug; it is a configuration problem

As usual, the ant error message is completely unhelpful, though for once it’s at least technically correct. (Most of the time when ant says, “This is not a bug; it is a configuration problem”, it is in fact a bug and not a configuration problem.) Here’s what’s really happening.

The jsch jar file distributed from http://www.jcraft.com/jsch/ is corrupt. Either they uploaded it wrong or they misconfigured their web server or both. The jar file with the relevant classes is there, but it’s no good. You can check your local copy by trying to list its contents with jar tvf:

$ jar tvf /usr/share/ant/lib/jsch*jar
java.util.zip.ZipException: error in opening zip file
	at java.util.zip.ZipFile.open(Native Method)
	at java.util.zip.ZipFile.(ZipFile.java:114)
	at java.util.zip.ZipFile.(ZipFile.java:75)
	at sun.tools.jar.Main.list(Main.java:979)
	at sun.tools.jar.Main.run(Main.java:224)
	at sun.tools.jar.Main.main(Main.java:1149)

If you see anything but a list of classes, the problem is that the JSCH jar is no good. To fix it, download the jar from sourceforge instead.

Once again I am reminded of the perils of depending on external libraries, especially ones you don’t build or distribute with your own product. In 2010 ssh and scp are mandatory features of any build and deployment system. Secure communications are too important to be left to random third party web sites.