filter的应用

public void (ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;

		boolean loginError = isErrorPage(request);
		boolean logoutSuccess = isLogoutSuccess(request);
		if (isLoginUrlRequest(request) || loginError || logoutSuccess) {
			String loginPageHtml = generateLoginPageHtml(request, loginError,
					logoutSuccess);
			response.setContentType("text/html;charset=UTF-8");
			response.setContentLength(loginPageHtml.length());
			response.getWriter().write(loginPageHtml);

			return;
		}

		chain.doFilter(request, response);
	}

if (ase != null) {
	handleSpringSecurityException(request, response, chain, ase);
}