之前一直沒有用過多線程皮钠，這次贩绕，寫了一個(gè)多線程查詢數(shù)據(jù)庫的案列，并且比較一下多線程和單線程直接執(zhí)行的效率壶愤，體會(huì)一下多線程同步淑倾。數(shù)據(jù)庫中大概有1 W條數(shù)據(jù)。下面是核心代碼：

單線程一次查詢數(shù)據(jù)庫

TestServiceImpl類

    @Override
    public List<Store> queryStoresInfo() {
        return testDao.queryStoresInfo();
    }

單線程For循環(huán)查詢數(shù)據(jù)庫

TestServiceImpl類

    @Override
    public List<Store> queryStoresInfoByFor() {
        List<Store> lists = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            List<Store> list = testDao.queryStoresInfo();
            lists.addAll(list);
        }
        return lists;
    }

多線程查詢數(shù)據(jù)庫(使用join()進(jìn)行同步)

TestServiceImpl類（下面這個(gè)是我的一個(gè)錯(cuò)誤的做法）

將join寫在循環(huán)內(nèi)征椒，實(shí)際本身還是一個(gè)串行的運(yùn)行過程娇哆。

    @Override
    public List<Store> queryStoresInfoByThread() throws InterruptedException {
        List<Store> lists = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            Thread thread = new Thread(new TestThread(lists));
            thread.start();
            thread.join();
        }
        return lists;
    }

TestServiceImpl類（正確的做法）

    @Override
    public List<Store> queryStoresInfoByThread() throws InterruptedException {
        List<Store> lists = new ArrayList<>();
        List<Thread> threads = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            Thread thread = new Thread(new TestThread(lists));
            thread.start();
            threads.add(thread);
        }
        for (Thread thread: threads){
            thread.join();
        }
        return lists;
    }

TestThread類

public class TestThread implements Runnable {

    TestDao testDao = SpringBeanUtils.getBean(TestDao.class);

    private List<Store> stores;

    public TestThread(List<Store> stores) {
        this.stores = stores;
    }

    @Override
    public void run() {
        System.err.println(Thread.currentThread().getName() +" query data start...");
        List<Store> store = testDao.queryStoresInfo();
        synchronized (stores) {
            stores.addAll(store);
        }
        System.err.println(Thread.currentThread().getName() +" query data end...");
    }

}

多線程查詢數(shù)據(jù)庫(使用CountDownLatch進(jìn)行同步)

TestServiceImpl類

    @Override
    public List<Store> queryStoresInfoByThread() throws InterruptedException {
        List<Store> lists = new ArrayList<>();
        CountDownLatch latch = new CountDownLatch(10);

        for (int i = 0; i < 10; i++) {
            Thread thread = new Thread(new TestThread(lists, latch));
            thread.start();
        }
        latch.await();
        return lists;
    }

TestThread類

public class TestThread implements Runnable {

    TestDao testDao = SpringBeanUtils.getBean(TestDao.class);

    private List<Store> stores;

    private CountDownLatch latch;

    public TestThread(List<Store> stores,CountDownLatch latch) {
        this.stores = stores;
        this.latch = latch;
    }

    @Override
    public void run() {
        System.err.println(Thread.currentThread().getName() +" query data start...");
        List<Store> store = testDao.queryStoresInfo();
        synchronized (stores) {
            stores.addAll(store);
        }
        latch.countDown();
        System.err.println(Thread.currentThread().getName() +" query data end...");
    }

}

多線程查詢數(shù)據(jù)庫(使用線程池->CountDownLatch進(jìn)行同步)

TestServiceImpl類

    @Override
    public List<Store> queryStoresInfoByThreadPool() {
        ExecutorService executorService = new ThreadPoolExecutor(5, 10, 1, TimeUnit.MINUTES,new ArrayBlockingQueue<Runnable>(10));

        List<Store> resultList = new ArrayList<>();
        CountDownLatch latch = new CountDownLatch(10);

        for (int i = 0; i < 10; i++) {
            executorService.execute(new TestThread(resultList,latch));
        }
        executorService.shutdown();
        try {
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        return resultList;
    }

TestThread類

public class TestThread implements Runnable {

    TestDao testDao = SpringBeanUtils.getBean(TestDao.class);

    private List<Store> stores;

    private CountDownLatch latch;

    public TestThread(List<Store> stores,CountDownLatch latch) {
        this.stores = stores;
        this.latch = latch;
    }

    @Override
    public void run() {
        System.err.println(Thread.currentThread().getName() +" query data start...");
        List<Store> store = testDao.queryStoresInfo();
        synchronized (stores) {
            stores.addAll(store);
        }
        latch.countDown();
        System.err.println(Thread.currentThread().getName() +" query data end...");
    }

}

運(yùn)行效率比較