关于java:聊聊cheddar的PendingResult

序

本文次要钻研一下 cheddar 的 PendingResult

PendingResult

Cheddar/cheddar/cheddar-application/src/main/java/com/clicktravel/cheddar/application/pending/result/PendingResult.java

class PendingResult {

    private static final long TIMEOUT_SECONDS = 30;
    private final CountDownLatch countdownLatch = new CountDownLatch(1);
    private Result result;

    /**
     * Offers a {@link Result}, returning immediately.
     * @param result {@link Result} to offer
     */
    public void offerResult(final Result result) {
        this.result = result;
        countdownLatch.countDown();}

    /**
     * Polls for a {@link Result}, blocking until it is offered by some other thread. If the result has already been
     * offered, the result is returned immediately.
     * @return {@link Result} obtained, potentially after blocking
     * @throws InterruptedException, PendingResultTimeoutException
     */
    public Result pollResult() throws InterruptedException, PendingResultTimeoutException {if (!countdownLatch.await(TIMEOUT_SECONDS, TimeUnit.SECONDS)) {throw new PendingResultTimeoutException();
        }
        return result;
    }
}

PendingResult 定义了 offerResult、pollResult 办法；offerResult 办法设置 result，而后通过 countdownLatch 通过 pollResult；pollResult 办法期待 TIMEOUT_SECONDS，若还没有后果抛出 PendingResultTimeoutException

PendingResultHandler

Cheddar/cheddar/cheddar-application/src/main/java/com/clicktravel/cheddar/application/pending/result/PendingResultHandler.java

@Component
public class PendingResultHandler {

    private final PendingResultsHolder pendingResultsHolder;
    private final String applicationName;
    private final XStream xStream = new XStream();

    @Autowired
    public PendingResultHandler(final PendingResultsHolder pendingResultsHolder,
            @Value("${server.application.name}") final String applicationName) {
        this.pendingResultsHolder = pendingResultsHolder;
        this.applicationName = applicationName;
    }

    /**
     * Creates a {@link PendingResult} stored on the local application instance
     * @return pendingResultId Unique identifier of created {@PendingResult}
     */
    public String createPendingResult() {return pendingResultsHolder.create();
    }

    /**
     * Removes a {@link PendingResult} stored on the local application instance
     * @param pendingResultId ID of {@link PendingResult} to remove
     */
    public void removePendingResult(final String pendingResultId) {pendingResultsHolder.remove(pendingResultId);
    }

    /**
     * Polls a {@link PendingResult} stored on the local application instance for a returned value, blocking until a
     * value is offered or an exception is thrown
     * @param pendingResultId ID of locally stored {@link PendingResult}
     * @return Value from returned result
     * @throws Exception If exception was thrown
     */
    public Object pollValue(final String pendingResultId) throws Exception {final PendingResult pendingResult = pendingResultsHolder.get(pendingResultId);
        return pendingResult.pollResult().getValue();
    }

    /**
     * Offers a return value for a {@link PendingResult}, which is possibly stored on a different (remote) application
     * instance
     * @param pendingResultId ID of {@link PendingResult} to offer value to
     * @param value Value to offer
     */
    public void offerValue(final String pendingResultId, final Object value) {offerResult(pendingResultId, new SimpleResult(value));
    }

    /**
     * Offers a thrown exception for a {@link PendingResult}, which is possibly stored on a different (remote)
     * application instance
     * @param pendingResultId of {@link PendingResult} to offer thrown exception to
     * @param exception Thrown exception to offer
     */
    public void offerException(final String pendingResultId, final Exception exception) {offerResult(pendingResultId, new ExceptionResult(exception));
    }

    private void offerResult(final String pendingResultId, final Result result) {final PendingResultOfferedEvent event = new PendingResultOfferedEvent();
        event.setTargetApplicationName(applicationName);
        event.setPendingResultId(pendingResultId);
        event.setResultXml(toCompactXml(result));
        SystemEventPublisher.instance().publishEvent(event);
    }

    private String toCompactXml(final Object object) {final StringWriter stringWriter = new StringWriter();
        xStream.marshal(object, new CompactWriter(stringWriter));
        return stringWriter.toString();}
}

PendingResultHandler 提供了 removePendingResult、pollValue、offerValue、offerException 办法；offerResult 办法创立并公布 PendingResultOfferedEvent

小结

cheddar 的 PendingResult 定义了 offerResult、pollResult 办法；PendingResultHandler 提供了 removePendingResult、pollValue、offerValue、offerException 办法。

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• Cheddar