java - 无法清楚理解java中的运行时监听器

Question

我有一段代码想要理解，我以前从未使用过运行时监听器，所以如果有人能给我指出一个很好的教程/帮助我理解这段代码的作用，我将不胜感激。

下面给出一个类的代码--

public interface ScraperRuntimeListener {

  public void onExecutionStart(Scraper scraper);

  public void onExecutionPaused(Scraper scraper);

  public void onExecutionContinued(Scraper scraper);

  public void onNewProcessorExecution(Scraper scraper, BaseProcessor processor);

  public void onExecutionEnd(Scraper scraper);

  public void onProcessorExecutionFinished(Scraper scraper, BaseProcessor processor, Map properties);

  public void onExecutionError(Scraper scraper, Exception e);

}

下面给出的是“Scraper”类的一些代码 - 我仅在下面给出引用我上面给出的代码的类(scraper 运行时监听器类)的代码...

首先有一个类成员声明部分--

  private List<ScraperRuntimeListener> scraperRuntimeListeners = new LinkedList<ScraperRuntimeListener>();

然后是一些利用上面类的函数---

 public Variable execute(List<IElementDef> ops) {
    this.setStatus(STATUS_RUNNING);

    // inform al listeners that execution is just about to start
    for (ScraperRuntimeListener listener: scraperRuntimeListeners) {
        listener.onExecutionStart(this);
    }

    try {
        for (IElementDef elementDef: ops) {
            BaseProcessor processor = ProcessorResolver.createProcessor(elementDef, this.configuration, this);
            if (processor != null) {
                processor.run(this, context);
            }
        }
    } finally {
        releaseDBConnections();
    }

    return new EmptyVariable();
}

public void setExecutingProcessor(BaseProcessor processor) {
    this.runningProcessors.push(processor);
    Iterator iterator = this.scraperRuntimeListeners.iterator();
    while (iterator.hasNext()) {
        ScraperRuntimeListener listener = (ScraperRuntimeListener) iterator.next();
        listener.onNewProcessorExecution(this, processor);
    }
}

 public void processorFinishedExecution(BaseProcessor processor, Map properties) {
    Iterator iterator = this.scraperRuntimeListeners.iterator();
    while (iterator.hasNext()) {
        ScraperRuntimeListener listener = (ScraperRuntimeListener) iterator.next();
        listener.onProcessorExecutionFinished(this, processor, properties);
    }
}


 public void addRuntimeListener(ScraperRuntimeListener listener) {
    this.scraperRuntimeListeners.add(listener);
}

 public void removeRuntimeListener(ScraperRuntimeListener listener) {
    this.scraperRuntimeListeners.remove(listener);
}

public synchronized int getStatus() {
    return status;
}

private synchronized void setStatus(int status) {
    this.status = status;
}

public void stopExecution() {
    setStatus(STATUS_STOPPED);
}

public void exitExecution(String message) {
    setStatus(STATUS_EXIT);
    this.message = message;
}


   public void continueExecution() {
    if (this.status == STATUS_PAUSED) {
        setStatus(STATUS_RUNNING);

        // inform al listeners that execution is continued
        Iterator listenersIterator = this.scraperRuntimeListeners.iterator();
        while (listenersIterator.hasNext()) {
            ScraperRuntimeListener listener = (ScraperRuntimeListener) listenersIterator.next();
            listener.onExecutionContinued(this);
        }
    }
}

/**
 * Inform all scraper listeners that an error has occured during scraper execution.
 */
  public void informListenersAboutError(Exception e) {
    setStatus(STATUS_ERROR);

    // inform al listeners that execution is continued
    Iterator listenersIterator = this.scraperRuntimeListeners.iterator();
    while (listenersIterator.hasNext()) {
        ScraperRuntimeListener listener = (ScraperRuntimeListener) listenersIterator.next();
        listener.onExecutionError(this, e);
    }
}

Answer 1

代码使用 observer pattern 。抓取器通过调用监听器(或观察者)的方法来通知监听器(或观察者)何时开始、何时完成、何时暂停等。