com.wk.wechat4j.base.util.SettableFuture.java Source code

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Here is the source code for com.wk.wechat4j.base.util.SettableFuture.java

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/*
 * Copyright 2002-2014 the original author or authors.
 *
 * 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 com.wk.wechat4j.base.util;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicReference;

/**
 * A {@link org.springframework.util.concurrent.ListenableFuture
 * ListenableFuture} whose value can be set via {@link #set(Object)} or
 * {@link #setException(Throwable)}. It may also be cancelled.
 *
 * <p>
 * Inspired by {@code com.google.common.util.concurrent.SettableFuture}.
 *
 * @author Mattias Severson
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class SettableFuture<T> implements Future<T> {

    private final SettableTask<T> settableTask;

    private final FutureTask<T> futureTask;

    public SettableFuture() {
        this.settableTask = new SettableTask<T>();
        this.futureTask = new FutureTask<T>(this.settableTask);
    }

    /**
     * Set the value of this future. This method will return {@code true} if the
     * value was set successfully, or {@code false} if the future has already
     * been set or cancelled.
     * 
     * @param value
     *            the value that will be set.
     * @return {@code true} if the value was successfully set, else
     *         {@code false}.
     */
    public boolean set(T value) {
        boolean success = this.settableTask.setValue(value);
        if (success) {
            this.futureTask.run();
        }
        return success;
    }

    /**
     * Set the exception of this future. This method will return {@code true} if
     * the exception was set successfully, or {@code false} if the future has
     * already been set or cancelled.
     * 
     * @param exception
     *            the value that will be set.
     * @return {@code true} if the exception was successfully set, else
     *         {@code false}.
     */
    public boolean setException(Throwable exception) {
        boolean success = this.settableTask.setException(exception);
        if (success) {
            this.futureTask.run();
        }
        return success;
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        this.settableTask.setCancelled();
        boolean cancelled = this.futureTask.cancel(mayInterruptIfRunning);
        if (cancelled && mayInterruptIfRunning) {
            interruptTask();
        }
        return cancelled;
    }

    @Override
    public boolean isCancelled() {
        return this.futureTask.isCancelled();
    }

    @Override
    public boolean isDone() {
        return this.futureTask.isDone();
    }

    /**
     * Retrieve the value.
     * <p>
     * Will return the value if it has been set via {@link #set(Object)}, throw
     * an {@link ExecutionException} if it has been set via
     * {@link #setException(Throwable)} or throw a
     * {@link java.util.concurrent.CancellationException} if it has been
     * cancelled.
     * 
     * @return The value associated with this future.
     */
    @Override
    public T get() throws InterruptedException, ExecutionException {
        return this.futureTask.get();
    }

    /**
     * Retrieve the value.
     * <p>
     * Will return the value if it has been set via {@link #set(Object)}, throw
     * an {@link ExecutionException} if it has been set via
     * {@link #setException(Throwable)} or throw a
     * {@link java.util.concurrent.CancellationException} if it has been
     * cancelled.
     * 
     * @param timeout
     *            the maximum time to wait.
     * @param unit
     *            the time unit of the timeout argument.
     * @return The value associated with this future.
     */
    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        return this.futureTask.get(timeout, unit);
    }

    /**
     * Subclasses can override this method to implement interruption of the
     * future's computation. The method is invoked automatically by a successful
     * call to {@link #cancel(boolean) cancel(true)}.
     * <p>
     * The default implementation does nothing.
     */
    protected void interruptTask() {
    }

    private static class SettableTask<T> implements Callable<T> {

        private static final String NO_VALUE = SettableFuture.class.getName() + ".NO_VALUE";

        private final AtomicReference<Object> value = new AtomicReference<Object>(NO_VALUE);

        private volatile boolean cancelled = false;

        public boolean setValue(T value) {
            if (this.cancelled) {
                return false;
            }
            return this.value.compareAndSet(NO_VALUE, value);
        }

        public boolean setException(Throwable exception) {
            if (this.cancelled) {
                return false;
            }
            return this.value.compareAndSet(NO_VALUE, exception);
        }

        public void setCancelled() {
            this.cancelled = true;
        }

        @SuppressWarnings("unchecked")
        @Override
        public T call() throws Exception {
            if (value.get() instanceof Exception) {
                throw (Exception) value.get();
            }
            return (T) value.get();
        }
    }

}