Under Apache Tomcat, how could my JSP files can access Beans under directories other than 'WEB-INF/classes' or 'WEB-INF/lib'?

You need to append the path of the directory containing the beans to the CLASSPATH variable within the bin/tomcat.bat file.

For instance, if your bean is located within c:classesMyBean.class
modify CLASSPATH as:
set classpath=%classpath%;c:classes