Cause: the class org.apache.tools.ant.taskdefs.optional.junit.JUnitTask was not found

具体错误：

BUILD FAILED
/home/tsit/jna-5.5.0/build.xml:1253: The following error occurred while executing this line:
/home/tsit/jna-5.5.0/contrib/platform/build.xml:224: Problem: failed to create task or type junit
Cause: the class org.apache.tools.ant.taskdefs.optional.junit.JUnitTask was not found.
        This looks like one of Ant's optional components.
Action: Check that the appropriate optional JAR exists in
        -/usr/share/ant/lib
        -/home/tsit/.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

缺少ant-junit.jar。怎么办？

只需要复制ant-junit.jar即可。