在多次 POST/DELETE/PUT 后仅运行一次功能（例如清理）

Question

我的网站上的流量可能会变得很重，我想放慢运行昂贵的清理功能的频率；我也想在后台运行它。

我使用removingListener 实现了一个缓存，并希望它在创建条目后30 秒异步运行，但我发现它要么根本不运行，要么立即运行。当它运行时，我还必须等待清理脚本。我是否误解了缓存和删除侦听器的目的？

@Path("my-endpoint")
public class MyResource{

    private static final Cache<String, String> debounceCleaner = CacheBuilder
        .newBuilder()
        .maximumSize(1000)
        .expireAfterWrite(30, TimeUnit.SECONDS)
        .removalListener((RemovalListener<String, String>) x-> new Cleaner().clean())
        .build();

    @PUT
    public Response update(){
        ...

        try{
            debounceCleaner.get("foo", ()->"bar");
        } catch (ExecutionException ex){
            throw new IllegalStateException("Unhandled", ex);
        }

        return Response(...)

Answer 1

缓存过期不打算用作去抖动器。其他问题已经在不同程度上回答了如何创建去抖动器。

implementing debounce in Java Deliver the first item immediately, 'debounce' following items

我为这个应用写了一个去抖动器如下：

public class Debouncer {

    private final int TIMEOUT = 30000;
    private Runnable runnable;
    private Thread backgroundRunnerLoop;
    private Date lastRun = null;
    private Date lastRequest = null;

    public Debouncer(Runnable runnable) {
        this.runnable = runnable;
        this.backgroundRunnerLoop = new Thread(() -> {
            while (true) {
                try {
                    Thread.sleep(TIMEOUT);
                    if (lastRequest != null && (lastRun == null || lastRun.before(DateUtils.addMilliseconds(lastRequest, TIMEOUT)))) {
                        this.runnable.run();
                        lastRun = new Date();
                    }
                } catch (Exception ex) {
                    throw new IllegalStateException("Debouncer loop broke.", ex);
                }
            }
        });
    }

    public void start() {
        if(!backgroundRunnerLoop.isAlive()){
            backgroundRunnerLoop.start();
        }
    }

    public void resetTimer() {
        lastRequest = new Date();
    }
}

我这样实例化它

@Path("my-endpoint")
public class MyResource {
    private static final Debouncer debouncer = new Debouncer(() -> new Cleaner().run());

    public MyResource() {
        debouncer.start();
    }

    @PUT
    public Response update(){
        // ...
        debouncer.resetTimer();

        return Response.noContent(...).build();
    }
}