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| <p><span class="bodyBlack"> |
| The short explanation is that the parent doesn't have all the classes it needs as some of them |
| are only in the child classloader, where the parent can't see them. |
| </span></p> |
| <p><span class="bodyBlack"> |
| This would occur, for example, if a class was loaded by the parent classloader, but that |
| class' superclass wasn't visible to the parent classloader, perhaps because it is only in the |
| child classloader. |
| </span></p> |
| <p><span class="bodyBlack"> |
| Here is a more concrete example: |
| <span class="code-block"> |
| public interface Person extends EJBObject { |
| } |
| |
| public interface Employee extends Person { |
| } |
| </span> |
| </span></p> |
| <p><span class="bodyBlack"> |
| Ok, so when we build our ejb jar, we put both the Person and Employee interfaces in the jar, so |
| everything should be good (so we think). But now let's say that for some reason the Employee interface is |
| also in another jar and that jar was loaded into the system classpath. |
| </span></p> |
| <p><span class="bodyBlack"> |
| When a new classloader is create for my ejb-jar at runtime and the system attempts to load the |
| Employee interface, the call goes right through that classloader and down to the system classloader. |
| The Employee interface is found, because it was accidentally added to that extra jar in the system |
| classpath. So now the system classloader goes looking for Employee's superinterface, Person, |
| where it immediatly blows up and throws a NoClassDefFoundError: Person. |
| </span></p> |
| <p><span class="bodyBlack"> |
| Most people will look at their ejb-jar and think, "But all my classes are there!?", which is |
| true. It really doesn't matter though, because one of those classes is also in the parent |
| classloader. The first call to load that class will bypass your classloader completely and |
| go to the parent. Once there, it is the parent's job to find *all* the dependent classes. |
| If it can't ... NoClassDefFoundError. |
| </span></p> |
| </answer></td></tr></table></td><td align="left" valign="top" height="5" width="240"> |
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