How to get javadocs on method and find tags in them

Problem:
Input:
A PsiClass and its PsiMethods like:
/**
* provides cache clearing service.
* @param cache the target cache
* @return  number of records removed
*/
public int clearCache(Cache cache) {
   ...
}

Output:
Build a map records method and their @param contents in their javadoc
Map<Method, Map<String, String>> = {{Method:xxx.clearCache(Cache) = {cache = the target cache}}}

I can't find a method to get the javadoc of the method and tags in it.