DelegatingFilterProxy.java

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain)
    throws ServletException, IOException {

  // Lazily initialize the delegate if necessary.
  Filter delegateToUse = this.delegate;
  if (delegateToUse == null) {
    synchronized (this.delegateMonitor) {
      delegateToUse = this.delegate;
      if (delegateToUse == null) {
        WebApplicationContext wac = findWebApplicationContext();
        if (wac == null) {
          throw new IllegalStateException("No WebApplicationContext found: " +
              "no ContextLoaderListener or DispatcherServlet registered?");
        }
        delegateToUse = initDelegate(wac);
      }
      this.delegate = delegateToUse;
    }
  }

  // Let the delegate perform the actual doFilter operation.
  invokeDelegate(delegateToUse, request, response, filterChain);
}

protected void invokeDelegate(
		Filter delegate, ServletRequest request, ServletResponse response, FilterChain filterChain)
		throws ServletException, IOException {

	delegate.doFilter(request, response, filterChain);
}