设计模式之命令模式 Java实例讲解 + 线程池中的应用场景

package com.alibaba.design.commandpattern;
/**
 * @author zhouyanxiang
 * @create 2020-08-2020/8/1-8:57
 */
public interface Order {
    void execute();
}

package com.alibaba.design.commandpattern;
/**
 * @author zhouyanxiang
 * @create 2020-08-2020/8/1-8:57
 */
public class Stock {
    private String name = "Tom";
    private int quantity = 10;
    public void buy(){
        System.out.println("Stock [ Name: "+name+", Quantity: " + quantity +" ] bought");
    }
    public void sell(){
        System.out.println("Stock [ Name: "+name+", Quantity: " + quantity +" ] sold");
    }
}

package com.alibaba.design.commandpattern;
/**
 * @author zhouyanxiang
 * @create 2020-08-2020/8/1-8:59
 */
public class BuyStock implements Order {
    private Stock abcStock;
    public BuyStock(Stock abcStock){
        this.abcStock = abcStock;
    }
    @Override
    public void execute() {
        abcStock.buy();
    }
}

package com.alibaba.design.commandpattern;
/**
 * @author zhouyanxiang
 * @create 2020-08-2020/8/1-9:00
 */
public class SellStock implements Order {
    private Stock abcStock;
    public SellStock(Stock abcStock){
        this.abcStock = abcStock;
    }
    @Override
    public void execute() {
        abcStock.sell();
    }
}

package com.alibaba.design.commandpattern;
import java.util.ArrayList;
import java.util.List;
/**
 * @author zhouyanxiang
 * @create 2020-08-2020/8/1-9:01
 */
public class Broker {
    private List<Order> orderList = new ArrayList<Order>();
    public void takeOrder(Order order){
        orderList.add(order);
    }
    public void placeOrders(){
        for (Order order : orderList) {
            order.execute();
        }
        orderList.clear();
    }
}

package com.alibaba.design.commandpattern;
/**
 * @author zhouyanxiang
 * @create 2020-08-2020/8/1-9:02
 */
public class CommandPatternDemo {
    public static void main(String[] args) {
        Stock abcStock = new Stock();
        BuyStock buyStockOrder = new BuyStock(abcStock);
        SellStock sellStockOrder = new SellStock(abcStock);
        Broker broker = new Broker();
        broker.takeOrder(buyStockOrder);
        broker.takeOrder(sellStockOrder);
        broker.placeOrders();
    }
}

/**
     * Executes the given task sometime in the future.  The task
     * may execute in a new thread or in an existing pooled thread.
     *
     * If the task cannot be submitted for execution, either because this
     * executor has been shutdown or because its capacity has been reached,
     * the task is handled by the current {@code RejectedExecutionHandler}.
     *
     * @param command the task to execute
     * @throws RejectedExecutionException at discretion of
     *         {@code RejectedExecutionHandler}, if the task
     *         cannot be accepted for execution
     * @throws NullPointerException if {@code command} is null
     */
    public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
        /*
         * Proceed in 3 steps:
         *
         * 1. If fewer than corePoolSize threads are running, try to
         * start a new thread with the given command as its first
         * task.  The call to addWorker atomically checks runState and
         * workerCount, and so prevents false alarms that would add
         * threads when it shouldn't, by returning false.
         *
         * 2. If a task can be successfully queued, then we still need
         * to double-check whether we should have added a thread
         * (because existing ones died since last checking) or that
         * the pool shut down since entry into this method. So we
         * recheck state and if necessary roll back the enqueuing if
         * stopped, or start a new thread if there are none.
         *
         * 3. If we cannot queue task, then we try to add a new
         * thread.  If it fails, we know we are shut down or saturated
         * and so reject the task.
         */
        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            reject(command);
    }
    /**
     * Initiates an orderly shutdown in which previously submitted
     * tasks are executed, but no new tasks will be accepted.
     * Invocation has no additional effect if already shut down.
     *
     * <p>This method does not wait for previously submitted tasks to
     * complete execution.  Use {@link #awaitTermination awaitTermination}
     * to do that.
     *
     * @throws SecurityException {@inheritDoc}
     */
    public void shutdown() {
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            checkShutdownAccess();
            advanceRunState(SHUTDOWN);
            interruptIdleWorkers();
            onShutdown(); // hook for ScheduledThreadPoolExecutor
        } finally {
            mainLock.unlock();
        }
        tryTerminate();
    }