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Shiro源码解析之SessionManager03-SessionValidationScheduler

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了解 SessionValidationScheduler

SessionValidationScheduler 会话验证调度器，定时调用方法 validateSessions() 验证session是否过期。其实例n在 AbstractValidatingSessionManager 中被声明。

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sessionManager 默认使 用ExecutorServiceSessionValidationSchedule，类继承图如下：

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类结构如下：

1571298835647

理解 SessionValidationScheduler

enableSessionValidation(): void

ExecutorServiceSessionValidationScheduler 中的实现：

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/**
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     * Creates a single thread {@link ScheduledExecutorService} to validate sessions at fixed intervals 
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     * and enables this scheduler. The executor is created as a daemon thread to allow JVM to shut down
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     */
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    //TODO Implement an integration test to test for jvm exit as part of the standalone example
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    // (so we don't have to change the unit test execution model for the core module)
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    public void enableSessionValidation() {
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        if (this.interval > 0l) {
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            // 真正的定时器
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            this.service = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {  
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	            private final AtomicInteger count = new AtomicInteger(1);
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	            public Thread newThread(Runnable r) {  
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	                Thread thread = new Thread(r);  
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	                thread.setDaemon(true);  
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	                thread.setName(threadNamePrefix + count.getAndIncrement());
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	                return thread;  
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	            }  
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            });        
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            // 启动定时器，看 `scheduleAtFixedRate` 源码注释理解该方法
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            this.service.scheduleAtFixedRate(this, interval, interval, TimeUnit.MILLISECONDS);
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        }
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        this.enabled = true;
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    }
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    public void run() {
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        if (log.isDebugEnabled()) {
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            log.debug("Executing session validation...");
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        }
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        long startTime = System.currentTimeMillis();
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        this.sessionManager.validateSessions();
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        long stopTime = System.currentTimeMillis();
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        if (log.isDebugEnabled()) {
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            log.debug("Session validation completed successfully in " + (stopTime - startTime) + " milliseconds.");
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        }
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    }

简译：以固定的时间间隔创建一个单线程来验证会话，并且开启这个调度。
scheduleAtFixedRate() 方法第一个参数以 Runnable 实现对象，里面一定是调用了 Runnable 对象的 run()

那么，是在什么时候开启的定时器呢？

这时我使用 Alt+F7来查找谁调用了 ExecutorServiceSessionValidationSchedule的enableSessionValidation() 方法。

AbstractVailidatingSessionManager 中 enableSessionValidation()

该方法调用了 SessionValidationScheduler的 enableSessionValidation；
而它自己又被本类中的 enableSessionValidationIfNecessary() 方法调用 ；
而 enableSessionValidationIfNecessary() 又被本类中的doGetSession()和createSession()方法调用。

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......
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   // line 83    
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private void enableSessionValidationIfNecessary() {
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       SessionValidationScheduler scheduler = getSessionValidationScheduler();
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       if (isSessionValidationSchedulerEnabled() && (scheduler == null || !scheduler.isEnabled())) {
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           enableSessionValidation();
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       }
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   }
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......
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   // line 112
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   @Override
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   protected final Session doGetSession(final SessionKey key) throws InvalidSessionException {
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       enableSessionValidationIfNecessary();
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       log.trace("Attempting to retrieve session with key {}", key);
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       Session s = retrieveSession(key);
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       if (s != null) {
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           validate(s, key);
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       }
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       return s;
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   }
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......
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   // line 134
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   protected Session createSession(SessionContext context) throws AuthorizationException {
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       enableSessionValidationIfNecessary();
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       return doCreateSession(context);
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   }
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......
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   // line 223    
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protected synchronized void enableSessionValidation() {
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       SessionValidationScheduler scheduler = getSessionValidationScheduler();
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       if (scheduler == null) {
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           scheduler = createSessionValidationScheduler();
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           setSessionValidationScheduler(scheduler);
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       }
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       // it is possible that that a scheduler was already created and set via 'setSessionValidationScheduler()'
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       // but would not have been enabled/started yet
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       if (!scheduler.isEnabled()) {
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           if (log.isInfoEnabled()) {
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               log.info("Enabling session validation scheduler...");
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           }
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           scheduler.enableSessionValidation();
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           afterSessionValidationEnabled();
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       }
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   }