org.apache.aurora.common.base.Closures.java Source code

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Here is the source code for org.apache.aurora.common.base.Closures.java

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/**
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.aurora.common.base;

import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

/**
 * Utilities for dealing with Closures.
 *
 * @author John Sirois
 */
public final class Closures {

    private static final Closure<?> NOOP = item -> {
        // noop
    };

    private Closures() {
        // utility
    }

    /**
     * Combines multiple closures into a single closure, whose calls are replicated sequentially
     * in the order that they were provided.
     * If an exception is encountered from a closure it propagates to the top-level closure and the
     * remaining closures are not executed.
     *
     * @param closures Closures to combine.
     * @param <T> Type accepted by the closures.
     * @return A single closure that will fan out all calls to {@link Closure#execute(Object)} to
     *    the wrapped closures.
     */
    public static <T> Closure<T> combine(Iterable<Closure<T>> closures) {
        checkNotNull(closures);
        checkArgument(Iterables.all(closures, Predicates.notNull()));

        final Iterable<Closure<T>> closuresCopy = ImmutableList.copyOf(closures);

        return item -> {
            for (Closure<T> closure : closuresCopy) {
                closure.execute(item);
            }
        };
    }

    /**
     * Applies a filter to a closure, such that the closure will only be called when the filter is
     * satisfied (returns {@code true}}.
     *
     * @param filter Filter to determine when {@code closure} is called.
     * @param closure Closure to filter.
     * @param <T> Type handled by the filter and the closure.
     * @return A filtered closure.
     */
    public static <T> Closure<T> filter(final Predicate<T> filter, final Closure<T> closure) {
        checkNotNull(filter);
        checkNotNull(closure);

        return item -> {
            if (filter.apply(item)) {
                closure.execute(item);
            }
        };
    }

    /**
     * Returns a closure that will do nothing.
     *
     * @param <T> The closure argument type.
     * @return A closure that does nothing.
     */
    @SuppressWarnings("unchecked")
    public static <T> Closure<T> noop() {
        return (Closure<T>) NOOP;
    }
}