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有这么一个问题，我们在一个后台界面维护一个关键词的数据，期望当关键词发生变化时，能立即加载到java内存当中。如果变化过于频繁，则没有必要每次变更都 重新加载。一秒内最多加载一次即可。 这个工具类就是为了解决这个问题。

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import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class SpanRunner {

    private final long span = 1000;
    Map<Runnable, Long> timeMap = new ConcurrentHashMap<>();
    Map<Runnable, Long> scheduleMap = new ConcurrentHashMap<>();

    ScheduledExecutorService schedule = new ScheduledThreadPoolExecutor(1);

    public void runSpan(Runnable runnable) {
        if (!timeMap.containsKey(runnable)) {
            timeMap.put(runnable, System.currentTimeMillis());
            runnable.run();
        } else {
            if (!scheduleMap.containsKey(runnable)) {
                long lastRun = timeMap.get(runnable);
                if (System.currentTimeMillis() - lastRun > span) {

                    timeMap.put(runnable, System.currentTimeMillis());
                    runnable.run();
                } else {
                    schedule.schedule(new Runnable() {
                        @Override public void run() {
                            timeMap.put(runnable, System.currentTimeMillis());

                            try {
                                runnable.run();
                            }catch (Exception e){
                                e.printStackTrace();
                            }finally {
                                scheduleMap.remove(runnable);
                            }
                        }
                    }, span, TimeUnit.MILLISECONDS);
                    scheduleMap.put(runnable, 1L);
                }
            }
        }
    }

}
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