如果孤立的发现某类的方法，不免使我们难以理解它的含义；当我们将对象的相互作用串起来的时候，更容易理解方法的意图
在对象之间相互通信时，首先应该了解对象的状态；最基本的入手方式就是 了解它的构造函数或者初始化方法以及执行相关方法后状态的变化，其次是相应方法的输入参数（发送消息）
当我们在后台建立一个爬行任务时，在Heritrix3.1.0系统里面对应一个爬行任务类，当前爬行任务的所有属性和行为都封装在这个爬行任务类里面
这个类为CrawlJob（org.archive.crawler.framework），我们先来熟悉一下该类的相关成员和方法
爬行任务CrawlJob类实现了两接口Comparable<CrawlJob>, ApplicationListener<ApplicationEvent>，前者显然是用于排序，后者是spring的事件监听器接口（事件监听模式）
CrawlJob类具有如下属性：
File primaryConfig; PathSharingContext ac; int launchCount; boolean isLaunchInfoPartial; DateTime lastLaunch; AlertThreadGroup alertThreadGroup; DateTime xmlOkAt = new DateTime(0L); Logger jobLogger;
这些属性我们暂时无从知道它们的具体作用，继续查看它的构造函数
public CrawlJob(File cxml) { primaryConfig = cxml; isLaunchInfoPartial = false; scanJobLog(); // XXX look at launch directories instead/first? alertThreadGroup = new AlertThreadGroup(getShortName()); }
在它的构造函数里面，初始化成员变量File primaryConfig 是任务配置文件crawler-beans.cxml，boolean isLaunchInfoPartial是否加载部分，scanJobLog()扫描日志，AlertThreadGroup alertThreadGroup线程组（本身用于发布日志记录）
当我们执行任务的build操作时，实际执行的是CrawlJob对象的void validateConfiguration()方法
/** * Does the assembled ApplicationContext self-validate? Any failures * are reported as WARNING log events in the job log. * * TODO: make these severe? */ public synchronized void validateConfiguration() { instantiateContainer(); if(ac==null) { // fatal errors already encountered and reported return; } ac.validate(); HashMap<String,Errors> allErrors = ac.getAllErrors(); for(String name : allErrors.keySet()) { for(Object err : allErrors.get(name).getAllErrors()) { LOGGER.log(Level.WARNING,err.toString()); } } }
继续调用void instantiateContainer()方法，这里是是实例化PathSharingContext ac（封装后的spring容器），并且设置当前CrawlJob对象为spring的监听器
/** * Can the configuration yield an assembled ApplicationContext? */ public synchronized void instantiateContainer() { checkXML(); if(ac==null) { try { ac = new PathSharingContext(new String[] {"file:"+primaryConfig.getAbsolutePath()},false,null); ac.addApplicationListener(this); ac.refresh(); getCrawlController(); // trigger NoSuchBeanDefinitionException if no CC getJobLogger().log(Level.INFO,"Job instantiated"); } catch (BeansException be) { // Calling doTeardown() and therefore ac.close() here sometimes // triggers an IllegalStateException and logs stack trace from // within spring, even if ac.isActive(). So, just null it. ac = null; beansException(be); } } }
后面是验证PathSharingContext ac的有效性（PathSharingContext类的方法）
// // Cascading self-validation // HashMap<String,Errors> allErrors; // bean name -> Errors public void validate() { allErrors = new HashMap<String,Errors>(); for(Entry<String, HasValidator> entry : getBeansOfType(HasValidator.class).entrySet()) { String name = entry.getKey(); HasValidator hv = entry.getValue(); Validator v = hv.getValidator(); Errors errors = new BeanPropertyBindingResult(hv,name); v.validate(hv, errors); if(errors.hasErrors()) { allErrors.put(name,errors); } } for(String name : allErrors.keySet()) { for(Object obj : allErrors.get(name).getAllErrors()) { LOGGER.fine("validation error for '"+name+"': "+obj); } } }
如果没有异常，此时CrawlJob对象的getJobStatusDescription为Ready
下一步我们执行任务的launch操作了，实际执行的是CrawlJob对象的void launch()方法
/** * Launch a crawl into 'running' status, assembling if necessary. * * (Note the crawl may have been configured to start in a 'paused' * state.) */ public synchronized void launch() { if (isProfile()) { throw new IllegalArgumentException("Can't launch profile" + this); } if(isRunning()) { getJobLogger().log(Level.SEVERE,"Can't relaunch running job"); return; } else { CrawlController cc = getCrawlController(); if(cc!=null && cc.hasStarted()) { getJobLogger().log(Level.SEVERE,"Can't relaunch previously-launched assembled job"); return; } } validateConfiguration(); if(!hasValidApplicationContext()) { getJobLogger().log(Level.SEVERE,"Can't launch problem configuration"); return; } //final String job = changeState(j, ACTIVE); // this temporary thread ensures all crawl-created threads // land in the AlertThreadGroup, to assist crawl-wide // logging/alerting alertThreadGroup = new AlertThreadGroup(getShortName()); alertThreadGroup.addLogger(getJobLogger()); Thread launcher = new Thread(alertThreadGroup, getShortName()+" launchthread") { public void run() { CrawlController cc = getCrawlController(); startContext(); if(cc!=null) { cc.requestCrawlStart(); } } }; getJobLogger().log(Level.INFO,"Job launched"); scanJobLog(); launcher.start(); // look busy (and give startContext/crawlStart a chance) try { Thread.sleep(1500); } catch (InterruptedException e) { // do nothing } }
关键方法是线程类Thread launcher里面的void startContext()和CrawlController对象的void requestCrawlStart()方法
void startContext()方法是启动spring容器里面的bean（实现了Lifecycle接口），调用bean的start方法）
/** * Start the context, catching and reporting any BeansExceptions. */ protected synchronized void startContext() { try { ac.start(); // job log file covering just this launch getJobLogger().removeHandler(currentLaunchJobLogHandler); File f = new File(ac.getCurrentLaunchDir(), "job.log"); currentLaunchJobLogHandler = new FileHandler(f.getAbsolutePath(), true); currentLaunchJobLogHandler.setFormatter(new JobLogFormatter()); getJobLogger().addHandler(currentLaunchJobLogHandler); } catch (BeansException be) { doTeardown(); beansException(be); } catch (Exception e) { LOGGER.log(Level.SEVERE,e.getClass().getSimpleName()+": "+e.getMessage(),e); try { doTeardown(); } catch (Exception e2) { e2.printStackTrace(System.err); } } }
CrawlController对象的void requestCrawlStart()方法
/** * Operator requested crawl begin */ public void requestCrawlStart() { hasStarted = true; sendCrawlStateChangeEvent(State.PREPARING, CrawlStatus.PREPARING); if(recoveryCheckpoint==null) { // only announce (trigger scheduling of) seeds // when doing a cold (non-recovery) start getSeeds().announceSeeds(); } setupToePool(); // A proper exit will change this value. this.sExit = CrawlStatus.FINISHED_ABNORMAL; if (getPauseAtStart()) { // frontier is already paused unless started, so just // 'complete'/ack pause completePause(); } else { getFrontier().run(); } }
该方法里面是导入seed种子文件，然后启动线程
protected void setupToePool() { toePool = new ToePool(alertThreadGroup,this); // TODO: make # of toes self-optimizing toePool.setSize(getMaxToeThreads()); toePool.waitForAll(); }
当我们执行任务的unpause操作时，实际执行的是CrawlController对象的void requestCrawlResume()方法
/** * Resume crawl from paused state */ public void requestCrawlResume() { if (state != State.PAUSING && state != State.PAUSED) { // Can't resume if not been told to pause return; } assert toePool != null; Frontier f = getFrontier(); f.unpause(); sendCrawlStateChangeEvent(State.RUNNING, CrawlStatus.RUNNING); }
pause指令 CrawlController void requestCrawlPause()
/** * Stop the crawl temporarly. */ public synchronized void requestCrawlPause() { if (state == State.PAUSING || state == State.PAUSED) { // Already about to pause return; } sExit = CrawlStatus.WAITING_FOR_PAUSE; getFrontier().pause(); sendCrawlStateChangeEvent(State.PAUSING, this.sExit); // wait for pause to come via frontier changes }
terminate指令 CrawlJob对象 void terminate()
public void terminate() { getCrawlController().requestCrawlStop(); }
继续调用CrawlController对象的void requestCrawlStop()方法
/** * Operator requested for crawl to stop. */ public synchronized void requestCrawlStop() { if(state == State.STOPPING) { // second stop request; nudge the threads with interrupts getToePool().cleanup(); } requestCrawlStop(CrawlStatus.ABORTED); }
teardown指令 CrawlJob对象 boolean teardown()
/** * Ensure a fresh start for any configuration changes or relaunches, * by stopping and discarding an existing ApplicationContext. * * @return true if teardown is complete when method returns, false if still in progress */ public synchronized boolean teardown() { CrawlController cc = getCrawlController(); if (cc != null) { cc.requestCrawlStop(); needTeardown = true; // wait up to 3 seconds for stop for(int i = 0; i < 11; i++) { if(cc.isStopComplete()) { break; } try { Thread.sleep(300); } catch (InterruptedException e) { // do nothing } } if (cc.isStopComplete()) { doTeardown(); } } assert needTeardown == (ac != null); return !needTeardown; }
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本系列Heritrix 3.1.0 源码解析系本人原创
转载请注明出处 博客园 刺猬的温驯
本文链接 http://www.cnblogs.com/chenying99/archive/2013/04/17/3025413.html