dt.jar is a JAR file that we currently include in the JDK with pre-generated BeanInfo classes and some resource files (images mostly).
As we move to a modular JDK then we need to decide what do with these issues. The main problem is that the BeanInfo classes are in the javax.swing package and this package is in our "desktop" module. We wat to avoid spliting packages between modules but at the same time we don't want to add additional footprint by including the BeanInfo classes in the runtime.
This bug is submitted to examine this issue. One suggestion proposed is that the BeanInfo classes move to the com.sun.beans.beaninfo package and that be in its own module (the desktop module could optionally depend on it).
It's not clear who uses this JAR file. NetBeans have reported that they use the BeanInfo classes but that they do so via the Introspector API, it doesn't matter to them if dt.jar exists or not.
One other thing to know is that there isn't a JCK issue here because these classes are excluded from the signature test.
At this time we would like to get the issue resolved for JDK8 (it's not an issue for 7u).