Java.lang.ClassNotFoundException: org.apache.log4j.Logger

Question

I got below error tried to load the first JSP in JDeveloper 11g. The log4j library is defined in the project. There is not compilation error. Please help!
ava.lang.NoClassDefFoundError: org/apache/log4j/Logger
     at jsp_servlet.__index._jspService(__index.java:98)
     at weblogic.servlet.jsp.JspBase.service(JspBase.java:34)
     at weblogic.servlet.internal.StubSecurityHelper$ServletServiceAction.run(StubSecurityHelper.java:227)
     at weblogic.servlet.internal.StubSecurityHelper.invokeServlet(StubSecurityHelper.java:125)
     at weblogic.servlet.internal.ServletStubImpl.execute(ServletStubImpl.java:292)
     Truncated. see log file for complete stacktrace

Answer 1

Did you read this part there:
There is a second possible issue that is specific to the commons-logging and related libraries when used with Integrated WLS and the configuration (which includes ADF) out-of-the-box. Because the commons-logging.jar is apparently in the system classpath, due to the way Java classloader delegation works, any log4j classes at the web application level are not visible to the logger factory by default. As long as this is the case, you may need to add the following to your web-application's WEB-INF/weblogic.xml:
<container-descriptor>
<prefer-web-inf-classes>true</prefer-web-inf-classes>
</container-descriptor>
What this does is tell the WLS JSP servlet to let web application classes override classes found in the system classloader. Standard Java classloader delegation gives the highest priority to the system classes.