I tried to run an Ant target within Eclipse today and got a fun error:

BUILD FAILED

java.lang.NoClassDefFoundError: com/sun/javadoc/Type

This happened because Ant could not find tools.jar, which contains classes to used to run javac and javadoc. The solution:

• Open up Window->Preferences->Java->Installed JREs
• Set your default JRE to a JDK/SDK
• Open up the one you just set as default, click “Add External JARs”, and then add tools.jar located in the JDK lib directory.