Does every J2EE server support symbolic link and what is the benefit from it? for flexibe and dynamic?
If by "symbolic link" you mean the JNDI name mapping (resource-ref) performed with the deployment descriptor, then the answer is yes, it's in the spec and vendors generally support it.
The benefit of using the mapping is deployment time flexibility, meaning that if for some reason the application assembler cannot use the same JNDI name as in the development environment, she can assign another JNDI name without modifying and recompiling the source code. Pretty important flexibility...