code: public Set entrySet() {
          if(_entrySet == null) {
              Map piMap = InternalUtils.getPageInputMap(_request);
              ArrayList list = new ArrayList();
              if(piMap != null) {
                  Iterator iterator = piMap.keySet().iterator();
                  while(iterator.hasNext()) {
                      Object name = iterator.next();
                      Object value = piMap.get(name);
                      list.add(new Entry(name, value));
                  }
              }
  
              _entrySet = new EntrySet((Entry[])list.toArray(new Entry[]{}));
          }
  
          return _entrySet;
      }
docs: Create a {@link java.util.Set} of page input entries.  This implementation
  assumes that the page input set does not change, which is acceptable for
  JSP clients as the page inputs have been specified when the JSP starts
  to render.
  
  @return Set