test3
看到subscribe(s -> System.out.println(s))没有执行。从上面可知switchIfEmpty的上一个操作返回空，则switchIfEmpty的下一个操作不会执行。但是无论如何switchIfEmpty对应的操作都会执行。例如上面的method1()都会执行。
二、认证流程
认证由AuthenticationWebFilter处理。AuthenticationWebFilter相当于SpringSecurity的UsernamePasswordAuthenticationFilter。

AuthenticationWebFilter实现了WebFilter接口：
    public interface WebFilter {
    	Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain);
AuthenticationWebFilter#filter
@Override
public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
	return this.requiresAuthenticationMatcher.matches(exchange).filter((matchResult) -> matchResult.isMatch())
			.flatMap((matchResult) -> this.authenticationConverter.convert(exchange))
			.switchIfEmpty(chain.filter(exchange).then(Mono.empty()))
			.flatMap((token) -> authenticate(exchange, chain, token))
			.onErrorResume(AuthenticationException.class, (ex) -> this.authenticationFailureHandler
					.onAuthenticationFailure(new WebFilterExchange(exchange, chain), ex));
ServerWebExchange相当于Servlet中的HttpServletRequest和HttpServletResponse。requiresAuthenticationMatcher在ServerHttpSecurity中是ServerWebExchangeMatchers.pathMatchers(HttpMethod.POST, loginPage),匹配post方式的登录接口。authenticationConverter是org.springframework.security.web.server.authentication.ServerAuthenticationConverter，用户将表单信息转换成Authentication。下一个操作是switchIfEmpty。如果Authentication为空就不会执行下一个操作authenticate（进行用户认证）。如果出现AuthenticationException异常，authenticationFailureHandler处理认证失败。
authenticationConverter默认是ServerFormLoginAuthenticationConverter：
@SuppressWarnings("deprecation")
public class ServerFormLoginAuthenticationConverter
		extends org.springframework.security.web.server.ServerFormLoginAuthenticationConverter
		implements ServerAuthenticationConverter {
	@Override
	public Mono<Authentication> convert(ServerWebExchange exchange) {
		return apply(exchange);
如果要自定义解析参数，可以实现org.springframework.security.web.server.authentication.ServerAuthenticationConverter接口。 convert调用了org.springframework.security.web.server.ServerFormLoginAuthenticationConverter的apply:
private String usernameParameter = "username";
private String passwordParameter = "password";
@Override
@Deprecated
public Mono<Authentication> apply(ServerWebExchange exchange) {
	return exchange.getFormData().map((data) -> createAuthentication(data));
private UsernamePasswordAuthenticationToken createAuthentication(MultiValueMap<String, String> data) {
	String username = data.getFirst(this.usernameParameter);
	String password = data.getFirst(this.passwordParameter);
	return UsernamePasswordAuthenticationToken.unauthenticated(username, password);
从请求中获取用户名和密码组装成UsernamePasswordAuthenticationToken。
再来看下AuthenticationWebFilter的authenticate：
private Mono<Void> authenticate(ServerWebExchange exchange, WebFilterChain chain, Authentication token) {
	return this.authenticationManagerResolver.resolve(exchange)
			.flatMap((authenticationManager) -> authenticationManager.authenticate(token))
			.switchIfEmpty(Mono.defer(
					() -> Mono.error(new IllegalStateException("No provider found for " + token.getClass()))))
			.flatMap((authentication) -> onAuthenticationSuccess(authentication,
					new WebFilterExchange(exchange, chain)))
			.doOnError(AuthenticationException.class,
					(ex) -> logger.debug(LogMessage.format("Authentication failed: %s", ex.getMessage())));
authenticationManagerResolver可以看作是认证管理器。调用authenticationManager.authenticate进行用户认证。authenticationManager默认是UserDetailsRepositoryReactiveAuthenticationManager。如果认证成功就调用onAuthenticationSuccess处理认证成功后的逻辑。
接下来看UserDetailsRepositoryReactiveAuthenticationManager，UserDetailsRepositoryReactiveAuthenticationManager继承了AbstractUserDetailsReactiveAuthenticationManager：
public Mono<Authentication> authenticate(Authentication authentication) {
	String username = authentication.getName();
	String presentedPassword = (String) authentication.getCredentials();
	// @formatter:off
	return retrieveUser(username)
			.doOnNext(this.preAuthenticationChecks::check)
			.publishOn(this.scheduler)
			.filter((userDetails) -> this.passwordEncoder.matches(presentedPassword, userDetails.getPassword()))
			.switchIfEmpty(Mono.defer(() -> Mono.error(new BadCredentialsException("Invalid Credentials"))))
			.flatMap((userDetails) -> upgradeEncodingIfNecessary(userDetails, presentedPassword))
			.doOnNext(this.postAuthenticationChecks::check)
			.map(this::createUsernamePasswordAuthenticationToken);
	// @formatter:on
retrieveUser通过用户名查询出UserDetails。接下来的操作和SpringSecurity中的类似。都是检查用户状态是否锁定，用户状态是否过期，密码是否过期，是否启用账户，以及进行密码对比等。
UserDetailsRepositoryReactiveAuthenticationManager#retrieveUser
protected Mono<UserDetails> retrieveUser(String username) {
	return this.userDetailsService.findByUsername(username);
调用ReactiveUserDetailsService通过用户名查询出UserDetails。如果要从数据库查询出用户。可以实现ReactiveUserDetailsService。
再看下AuthenticationWebFilter的authenticationFailureHandler,默认实现是new RedirectServerAuthenticationFailureHandler(loginPage + "?error")。重定向到登录页面并携带错误提示信息。
最后看AuthenticationWebFilter的onAuthenticationSuccess：
protected Mono<Void> onAuthenticationSuccess(Authentication authentication, WebFilterExchange webFilterExchange) {
	ServerWebExchange exchange = webFilterExchange.getExchange();
	SecurityContextImpl securityContext = new SecurityContextImpl();
	securityContext.setAuthentication(authentication);
	return this.securityContextRepository.save(exchange, securityContext)
			.then(this.authenticationSuccessHandler.onAuthenticationSuccess(webFilterExchange, authentication))
			.subscriberContext(ReactiveSecurityContextHolder.withSecurityContext(Mono.just(securityContext)));
securityContextRepository默认实现是WebSessionServerSecurityContextRepository。将Authentication保存到WebSession中。authenticationSuccessHandler实现是new RedirectServerAuthenticationSuccessHandler("/")。重定向到根路径。最后将securityContext设置到ReactiveSecurityContextHolder。