public class DocumentRESTFacade implements ServletContextAware  {
    @PersistenceContext(unitName = "PU")
    protected EntityManager entityManager;
    private String rootPath = null;
    ServletContext sc = null;

    public DocumentRESTFacade() {
    }

// тратата

    @Override
    public void setServletContext(ServletContext sc) {
        this.sc = sc;
    }

    private String getRootPath(){
        if(rootPath==null){
            rootPath = sc.getInitParameter("documentsPath");
            if(rootPath==null)
                rootPath = java.io.File.separator;
            else if(!rootPath.endsWith(java.io.File.separator))
                rootPath = rootPath + java.io.File.separator;
        }
        return rootPath;
    }

HttpServletRequest req = ((ServletRequestAttributes)RequestContextHolder.getRequestAttributes()).getRequest();