61 lines
1.8 KiB
Java
61 lines
1.8 KiB
Java
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package com.moparisthebest.jdbc.cache;
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import java.time.Duration;
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import java.time.Instant;
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import java.util.Objects;
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import java.util.function.Supplier;
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/**
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* This implements a simple cache, meant to be accessed concurrently from multiple threads, that is refreshed on a user
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* defined interval.
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*
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* Most often instances of this class will be `static final` so the entire application can benefit from the cache
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*
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* @param <T> type of cached item
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*/
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public class Cache<T> implements Supplier<T> {
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public static <T> Supplier<T> of(final Duration refreshInterval, final Supplier<T> supplier) {
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return new Cache<>(refreshInterval, supplier);
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}
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private final Duration refreshInterval;
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private Instant lastRefresh;
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protected final Supplier<T> supplier;
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protected T item;
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protected Cache(final Duration refreshInterval, final Supplier<T> supplier) {
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Objects.requireNonNull(refreshInterval);
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// we are explicitly allowing supplier to be null, in which case get() will fail
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this.refreshInterval = refreshInterval;
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this.supplier = supplier;
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// so refresh will be called immediately
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this.lastRefresh = Instant.MIN;
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}
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protected boolean shouldRefresh() {
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return Instant.now().isAfter(lastRefresh.plus(refreshInterval));
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}
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protected void markRefreshed() {
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this.lastRefresh = Instant.now();
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}
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@Override
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public T get() {
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if (shouldRefresh()) {
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// we want to refresh
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synchronized (this) {
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if (shouldRefresh()) {
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// maybe another thread beat us in here and already refreshed
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this.item = supplier.get();
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markRefreshed();
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}
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}
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}
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return item;
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}
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}
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