Spring Security3源码分析-LogoutFilter分析

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