Java中com.apollographql.apollo.api.internal.Optional.orNull()方法详解与示例

在 Java 开发中，com.apollographql.apollo.api.internal.Optional.orNull() 方法是一个非常实用的工具，用于处理可能为空的值。本文将详细介绍该方法的用法，并提供多个代码示例，帮助读者更好地理解其应用场景。

Optional.orNull 介绍

[英] Returns the contained instance if it is present; null otherwise. If the instance is known to be present, use #get() instead.
[中] 如果实例存在，则返回包含的实例；否则返回 null。如果已知实例存在，请使用 #get() 方法。

与 Java 的 java.util.Optional 类相比，Optional.orNull() 方法等同于 Java 8 中的 Optional.orElse(null)。

代码示例

以下是一些从 Apollo Android 和 AWS AppSync SDK 中提取的实际代码示例，展示了 Optional.orNull() 方法的具体用法。

示例 1：

private synchronized void activate(Optional> callback) throws ApolloCanceledException {
    switch (state.get()) {
        case IDLE:
            originalCallback.set(callback.orNull());
            tracker.registerQueryWatcher(this);
            break;
        case CANCELED:
            throw new ApolloCanceledException("Call is cancelled.");
        case TERMINATED:
        case ACTIVE:
            throw new IllegalStateException("Already Executed");
        default:
            throw new IllegalStateException("Unknown state");
    }
    state.set(ACTIVE);
}

示例 2：

private synchronized void activate(Optional callback) throws ApolloCanceledException {
    switch (state.get()) {
        case IDLE:
            originalCallback.set(callback.orNull());
            tracker.registerPrefetchCall(this);
            break;
        case CANCELED:
            throw new ApolloCanceledException("Call is cancelled.");
        case TERMINATED:
        case ACTIVE:
            throw new IllegalStateException("Already Executed");
        default:
            throw new IllegalStateException("Unknown state");
    }
    state.set(ACTIVE);
}

示例 3：

@SuppressWarnings("ResultOfMethodCallIgnored")
private synchronized void activate(Optional> callback) {
    switch (state.get()) {
        case IDLE:
            originalCallback.set(callback.orNull());
            tracker.registerCall(this);
            callback.apply(new Action>() {
                @Override public void apply(@NotNull Callback callback) {
                    callback.onStatusEvent(StatusEvent.SCHEDULED);
                }
            });
            break;
        case CANCELED:
            throw new ApolloCanceledException("Call is cancelled.");
        case TERMINATED:
        case ACTIVE:
            throw new IllegalStateException("Already Executed");
        default:
            throw new IllegalStateException("Unknown state");
    }
    state.set(ACTIVE);
}

示例 4：

public Builder toBuilder() {
    return new Builder(operation)
            .cacheHeaders(cacheHeaders)
            .fetchFromCache(fetchFromCache)
            .optimisticUpdates(optimisticUpdates.orNull());
}

示例 5：

@Nullable @Override public Record loadRecord(@NotNull final String key, @NotNull final CacheHeaders cacheHeaders) {
    checkNotNull(key, "key == null");
    checkNotNull(cacheHeaders, "cacheHeaders == null");
    try {
        final Optional nOnOptimisticRecord= nextCache()
                .flatMap(new Function>() {
                    @NotNull @Override public Optional apply(@NotNull NormalizedCache cache) {
                        return Optional.fromNullable(cache.loadRecord(key, cacheHeaders));
                    }
                });
        final RecordJournal journal = lruCache.getIfPresent(key);
        if (journal != null) {
            return nonOptimisticRecord.map(new Function() {
                @NotNull @Override public Record apply(@NotNull Record record) {
                    Record result = record.clone();
                    result.mergeWith(journal.snapshot);
                    return result;
                }
            }).or(journal.snapshot.clone());
        } else {
            return nonOptimisticRecord.orNull();
        }
    } catch (Exception ignore) {
        return null;
    }
}

测试示例：

@Test
public void testOrNullPresent() {
    assertEquals("a", Optional.of("a").orNull());
}

@Test
public void testOrNullAbsent() {
    assertNull(Optional.absent().orNull());
}