LogoutFilter过滤器对应的类路径为
org.springframework.security.web.authentication.logout.LogoutFilter
通过这个类的源码可以看出，这个类有两个构造函数
public LogoutFilter(LogoutSuccessHandler logoutSuccessHandler, LogoutHandler... handlers) {
Assert.notEmpty(handlers, "LogoutHandlers are required");
this.handlers = Arrays.asList(handlers);
Assert.notNull(logoutSuccessHandler, "logoutSuccessHandler cannot be null");
this.logoutSuccessHandler = logoutSuccessHandler;
}
public LogoutFilter(String logoutSuccessUrl, LogoutHandler... handlers) {
Assert.notEmpty(handlers, "LogoutHandlers are required");
this.handlers = Arrays.asList(handlers);
Assert.isTrue(!StringUtils.hasLength(logoutSuccessUrl) ||
UrlUtils.isValidRedirectUrl(logoutSuccessUrl), logoutSuccessUrl + " isn't a valid redirect URL");
SimpleUrlLogoutSuccessHandler urlLogoutSuccessHandler = new SimpleUrlLogoutSuccessHandler();
if (StringUtils.hasText(logoutSuccessUrl)) {
urlLogoutSuccessHandler.setDefaultTargetUrl(logoutSuccessUrl);
}
logoutSuccessHandler = urlLogoutSuccessHandler;
}
这两个构造函数的参数，是从哪里传递的呢？没错，就是之前解析http标签通过创建LogoutFilter过滤器的bean定义时通过构造参数注入进来的。下面的部分源码为LogoutFilter的bean定义
public BeanDefinition parse(Element element, ParserContext pc) {
String logoutUrl = null;
String successHandlerRef = null;
String logoutSuccessUrl = null;
String invalidateSession = null;
BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(LogoutFilter.class);
if (element != null) {
//分别解析logout标签的属性
Object source = pc.extractSource(element);
builder.getRawBeanDefinition().setSource(source);
logoutUrl = element.getAttribute(ATT_LOGOUT_URL);
successHandlerRef = element.getAttribute(ATT_LOGOUT_HANDLER);
WebConfigUtils.validateHttpRedirect(logoutUrl, pc, source);
logoutSuccessUrl = element.getAttribute(ATT_LOGOUT_SUCCESS_URL);
WebConfigUtils.validateHttpRedirect(logoutSuccessUrl, pc, source);
invalidateSession = element.getAttribute(ATT_INVALIDATE_SESSION);
}
if (!StringUtils.hasText(logoutUrl)) {
logoutUrl = DEF_LOGOUT_URL;
}
//向LogoutFilter中注入属性值filterProcessesUrl
builder.addPropertyValue("filterProcessesUrl", logoutUrl);
if (StringUtils.hasText(successHandlerRef)) {
if (StringUtils.hasText(logoutSuccessUrl)) {
pc.getReaderContext().error("Use " + ATT_LOGOUT_URL + " or " + ATT_LOGOUT_HANDLER + ", but not both",
pc.extractSource(element));
}
//如果successHandlerRef不为空，就通过构造函数注入到LogoutFilter中
builder.addConstructorArgReference(successHandlerRef);
} else {
// Use the logout URL if no handler set
if (!StringUtils.hasText(logoutSuccessUrl)) {
//如果logout-success-url没有定义，则采用默认的/
logoutSuccessUrl = DEF_LOGOUT_SUCCESS_URL;
}
//通过构造函数注入logoutSuccessUrl值
builder.addConstructorArgValue(logoutSuccessUrl);
}
if (!StringUtils.hasText(invalidateSession)) {
invalidateSession = DEF_INVALIDATE_SESSION;
}
//默认Logout的Handler是SecurityContextLogoutHandler
ManagedList handlers = new ManagedList();
SecurityContextLogoutHandler sclh = new SecurityContextLogoutHandler();
if ("true".equals(invalidateSession)) {
sclh.setInvalidateHttpSession(true);
} else {
sclh.setInvalidateHttpSession(false);
}
handlers.add(sclh);
//如果有remember me服务，需要添加remember的handler
if (rememberMeServices != null) {
handlers.add(new RuntimeBeanReference(rememberMeServices));
}
//继续将handlers通过构造参数注入到LogoutFilter的bean中
builder.addConstructorArgValue(handlers);
return builder.getBeanDefinition();
}
此时应该能知道，在LogoutFilter的bean实例化时，两个类变量logoutSuccessUrl、List<LogoutHandler> handlers已经通过构造函数注入到LogoutFilter的实例中来了。
接下来，继续看doFilter部分的源码
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
//判断是否需要退出，主要通过请求的url是否是filterProcessesUrl值来识别
if (requiresLogout(request, response)) {
//通过SecurityContext实例获取认证信息
Authentication auth = SecurityContextHolder.getContext().getAuthentication();
if (logger.isDebugEnabled()) {
logger.debug("Logging out user '" + auth + "' and transferring to logout destination");
}
//循环LogoutHandler处理退出任务
for (LogoutHandler handler : handlers) {
handler.logout(request, response, auth);
}
//退出成功后，进行redirect操作
logoutSuccessHandler.onLogoutSuccess(request, response, auth);
return;
}
chain.doFilter(request, response);
}
这时，可能会产生疑问。上一个过滤器SecurityContextPersistenceFilter不是只产生了一个空的SecurityContext么？就是一个没有认证信息的SecurityContext实例
Authentication auth = SecurityContextHolder.getContext().getAuthentication();
这个返回的不是null么？产生这个疑问，肯定是被SecurityContextPersistenceFilter过滤器分析时误导的。实际上，每个过滤器只处理自己负责的事情，LogoutFilter只负责拦截j_spring_security_logout这个url（如果没有配置logout的url），其他的url全部跳过。其实退出功能肯定是登录到应用之后才会使用到的，登录对应的Filter肯定会把认证信息添加到SecurityContext中去的，后面再分析。
继续看LogoutHandler是如何处理退出任务的
for (LogoutHandler handler : handlers) {
handler.logout(request, response, auth);
}
这里的handler至少有一个SecurityContextLogoutHandler，
如果有remember me服务，就还有一个Handler。remember me的handler有两种，
如果配置了持久化信息，如（token-repository-ref、data-source-ref属性）这种的handler为：org.springframework.security.web.authentication.rememberme.PersistentTokenBasedRememberMeServices
如果没有配置，那么handler就是：org.springframework.security.web.authentication.rememberme.TokenBasedRememberMeServices
先来看SecurityContextLogoutHandler
//完成两个任务1.让session失效；2.清除SecurityContext实例
public void logout(HttpServletRequest request, HttpServletResponse response, Authentication authentication) {
Assert.notNull(request, "HttpServletRequest required");
if (invalidateHttpSession) {
HttpSession session = request.getSession(false);
if (session != null) {
session.invalidate();
}
}
SecurityContextHolder.clearContext();
}
再来看remember me的handler
1.配置了持久化属性时的handler：PersistentTokenBasedRememberMeServices
//也完成两个任务1.清除cookie；2.从持久化中清除remember me数据
public void logout(HttpServletRequest request, HttpServletResponse response, Authentication authentication) {
super.logout(request, response, authentication);
if (authentication != null) {
//如果定义了token-repository-ref属性，则通过依赖的持久化bean清除
//如果定义了data-source-ref属性，直接通过
//JdbcTokenRepositoryImpl清除数据，也就是执行delete操作
tokenRepository.removeUserTokens(authentication.getName());
}
}
2.未配置持久化属性的handler：TokenBasedRememberMeServices
这个handler没有覆盖父类的logout方法，所以直接调用父类的logout方法，仅仅清除cookie
退出成功后执行onLogoutSuccess操作，完成redirect
logoutSuccessHandler.onLogoutSuccess(request, response, auth);
这个语句是直接redirect到logout标签中的logout-success-url属性定义的url
至此，整个logoutFilter任务已经完成了，总结一下，主要任务为
1.从SecurityContext中获取Authentication，然后调用每个handler处理logout
2.退出成功后跳转到指定的url
