Question

我有一段我想要理解的代码，我以前从未使用过运行时监听器，所以如果有人能指点我一个好的教程/帮助我理解这段代码的作用，我将不胜感激。< / p>

下面给出了一个类的代码 -

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'类中的一些代码 - 我只给出下面引用我上面给出的代码的代码（刮刀运行时监听器类）...

首先，类成员声明中有一节 -

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

然后有一些函数利用上面的类---

 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

代码正在使用observer pattern。刮刀通过调用方法，启动时，完成时，暂停时等通知听众（或观察者）。

Answer 2

我不完全确定我理解你的意思，但是如果你编写一个实现这个ScraperRuntimeListener的类并且同一个类实现Runnable，那么你可以将它提交到池中。在内部运行中，您可以注册（可能有一种方法可以执行此操作）此类可以作为侦听器。

无法清楚地了解java中的运行时监听器

2 个答案: