笔者打算写个轻量版的秒杀系统，那么需要多线程模拟客户去抢购某个商品。故有想先写一个简单的多线程抢票系统加深一下对线程池，同步的理解。
1. 新建Java project，命名为ClientApp1, src文件夹里面新建demo文件夹。
项目结构如下，
2. 程序模拟的场景用例如下，
- 多个线程模拟多个客户去购买春运车票
- 每个客户购买车票【0,9】，最少买0张，最多能买九张。
- 每个客户同步的买票，当某个线程在买票时，其他线程处于等待状态
- 所有客户线程买票完毕，主线程最后统计一共卖出多少张车票，切忌不能超卖。
- CountDownLatch这个类使主线程等待其他线程各自执行完毕后再执行。
3. 代码如下：
package demo;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import org.apache.log4j.Logger;
public class Ticket implements Runnable {
private Integer capacity; // 一共有多少张票
private Integer soldTickets = 0; // 最后总计售出多少张票
// CountDownLatch这个类使一个线程等待其他线程各自执行完毕后再执行。
// 是通过一个计数器来实现的，计数器的初始值是线程的数量。
// 每当一个线程执行完毕后，计数器的值就-1，当计数器的值为0时，表示所有线程都执行完毕，然后处于等待的线程就可以恢复工作了。
private CountDownLatch latch;
// 使用Log4j2写日志
private Logger log;
public void setLog(Logger log) {
this.log = log;
}
public Ticket(Integer c, CountDownLatch latch) {
// TODO Auto-generated constructor stub
this.capacity = c;
this.latch = latch;
}
public Integer getSoldTickets() {
return soldTickets;
}
@Override
public synchronized void run() {
// 每个线程客户购买0~9张票
int count = new Random().nextInt(10);
log.info(Thread.currentThread().getName() + " wants to buy tickets : " + count);
if(capacity >= count) {
capacity -= count;
soldTickets += count;
log.info(Thread.currentThread().getName() + " has bought tickets successfully. The left tikcets : " + capacity);
}
else {
log.info(String.format("Insufficient tickets[%d], stop trading now.", capacity));
}
latch.countDown();
}
}
package demo;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
public class TicketPractice {
private static ExecutorService pool;
private static CountDownLatch latch;
private static Integer NUMBER = 5000; // 客户线程数目
private static final Logger logger = LogManager.getLogger(TicketPractice.class);
public static void main(String[] args) {
// TODO Auto-generated method stub
pool = new ThreadPoolExecutor(100, NUMBER, 300, TimeUnit.SECONDS,
new LinkedBlockingQueue<Runnable>(NUMBER),Executors.defaultThreadFactory(),
new ThreadPoolExecutor.AbortPolicy());
latch = new CountDownLatch(NUMBER);
Ticket task = new Ticket(NUMBER, latch);
task.setLog(logger);
for(int i=0;i<NUMBER;++i) {
pool.execute(task);
}
try {
latch.await();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
logger.info("+++++++++++++++++++++++++++++++++++");
logger.info("Sold tickets in total : " + task.getSoldTickets());
logger.info("+++++++++++++++++++++++++++++++++++");
}
}
4. 值得一提的是，如使用Log4j2,需要引入外部三个jar包
- log4j-1.2-api-2.12.1.jar
- log4j-api-2.12.1.jar
- log4j-core-2.12.1.jar
Log4j2.xml内容如下，
<?xml version="1.0" encoding="UTF-8"?>
<!--日志级别以及优先级排序: OFF > FATAL > ERROR > WARN > INFO > DEBUG > TRACE > ALL -->
<!--Configuration后面的status，这个用于设置log4j2自身内部的信息输出，可以不设置，当设置成trace时，你会看到log4j2内部各种详细输出-->
<!--monitorInterval：Log4j能够自动检测修改配置 文件和重新配置本身，设置间隔秒数-->
<configuration status="INFO">
<!--先定义所有的appender -->
<appenders>
<!--这个输出控制台的配置 -->
<Console name="Console" target="SYSTEM_OUT">
<ThresholdFilter level="trace" onMatch="ACCEPT"
onMismatch="DENY" />
<PatternLayout
pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n" />
</Console>
<File name="log" fileName="D:/Log/log.txt" append="false">
<PatternLayout
pattern="%d{HH:mm:ss.SSS} %-5level %class{36} %L %M - %msg%xEx%n" />
</File>
</appenders>
<!--然后定义logger，只有定义了logger并引入的appender，appender才会生效 -->
<loggers>
<root level="trace">
<appender-ref ref="Console" />
<appender-ref ref="log" />
</root>
</loggers>
</configuration>
5. 运行程序，5000个客户线程随机买票，总票数5000张，不能超卖。程序运行日志如下，
22:11:10.317 INFO demo.Ticket 37 run - pool-2-thread-1 wants to buy tickets : 0 22:11:10.322 INFO demo.Ticket 41 run - pool-2-thread-1 has bought tickets successfully. The left tikcets : 5000 22:11:10.322 INFO demo.Ticket 37 run - pool-2-thread-100 wants to buy tickets : 6 22:11:10.322 INFO demo.Ticket 41 run - pool-2-thread-100 has bought tickets successfully. The left tikcets : 4994 22:11:10.323 INFO demo.Ticket 37 run - pool-2-thread-99 wants to buy tickets : 5 22:11:10.323 INFO demo.Ticket 41 run - pool-2-thread-99 has bought tickets successfully. The left tikcets : 4989 。。。。。。 。。。。。。 22:11:11.359 INFO demo.Ticket 37 run - pool-2-thread-3 wants to buy tickets : 2 22:11:11.359 INFO demo.Ticket 44 run - Insufficient tickets[0], stop trading now. 22:11:11.365 INFO demo.TicketPractice 38 main - +++++++++++++++++++++++++++++++++++ 22:11:11.366 INFO demo.TicketPractice 39 main - Sold tickets in total : 5000 22:11:11.366 INFO demo.TicketPractice 40 main - +++++++++++++++++++++++++++++++++++