To run Hibernate example, We must put log4jXXX.jar into the "ext" directory of JDK

To run Hibernate example successfully, We must place log4jXXX.jar into the "jre/ext" directory of JDK (like: JDK1.5.0_06). for example, we can run the example provided by Hibernate package: "ant eg".
otherwise, it will have an error:
java.lang.ExceptionInInitializerError at......
....
Caused by: org.apache.commons.logging.LogConfigurationException: org.apache.commons.logging.LogConfigurationException: No suitable Log constructor
.....