使用Java实现高并发编程
今天我们来讨论Java中的高并发编程。Java提供了丰富的并发编程工具和框架，包括线程、线程池、并发集合和锁机制等。本文将通过代码示例详细介绍如何使用这些工具实现高并发编程。
1. 线程的创建与管理
Java中创建线程的方式主要有两种：继承Thread类和实现Runnable接口。
继承Thread类
package cn.juwatech.concurrency;
public class MyThread extends Thread {
@Override
public void run() {
System.out.println("Thread " + Thread.currentThread().getId() + " is running");
}
public static void main(String[] args) {
MyThread thread1 = new MyThread();
MyThread thread2 = new MyThread();
thread1.start();
thread2.start();
}
}实现Runnable接口
package cn.juwatech.concurrency;
public class MyRunnable implements Runnable {
@Override
public void run() {
System.out.println("Thread " + Thread.currentThread().getId() + " is running");
}
public static void main(String[] args) {
Thread thread1 = new Thread(new MyRunnable());
Thread thread2 = new Thread(new MyRunnable());
thread1.start();
thread2.start();
}
}2. 线程池
线程池通过重用线程来提高性能，避免频繁创建和销毁线程。Java的Executor框架提供了多种线程池实现。
package cn.juwatech.concurrency;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadPoolExample {
public static void main(String[] args) {
ExecutorService executor = Executors.newFixedThreadPool(5);
for (int i = 0; i < 10; i++) {
executor.execute(() -> {
System.out.println("Thread " + Thread.currentThread().getId() + " is running");
});
}
executor.shutdown();
}
}3. 并发集合
Java提供了线程安全的并发集合，如ConcurrentHashMap、CopyOnWriteArrayList等，适用于高并发场景。
ConcurrentHashMap
package cn.juwatech.concurrency;
import java.util.concurrent.ConcurrentHashMap;
import java.util.Map;
public class ConcurrentHashMapExample {
public static void main(String[] args) {
Map<String, Integer> concurrentMap = new ConcurrentHashMap<>();
concurrentMap.put("A", 1);
concurrentMap.put("B", 2);
concurrentMap.put("C", 3);
concurrentMap.forEach((key, value) -> {
System.out.println("Key: " + key + ", Value: " + value);
});
}
}CopyOnWriteArrayList
package cn.juwatech.concurrency;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
public class CopyOnWriteArrayListExample {
public static void main(String[] args) {
List<String> list = new CopyOnWriteArrayList<>();
list.add("A");
list.add("B");
list.add("C");
list.forEach(item -> {
System.out.println("Item: " + item);
});
}
}4. 锁机制
Java提供了多种锁机制以确保线程安全，包括synchronized关键字、ReentrantLock和读写锁等。
synchronized关键字
package cn.juwatech.concurrency;
public class SynchronizedExample {
private int count = 0;
public synchronized void increment() {
count++;
}
public static void main(String[] args) {
SynchronizedExample example = new SynchronizedExample();
Runnable task = () -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
};
Thread thread1 = new Thread(task);
Thread thread2 = new Thread(task);
thread1.start();
thread2.start();
try {
thread1.join();
thread2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Final count: " + example.count);
}
}ReentrantLock
package cn.juwatech.concurrency;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class ReentrantLockExample {
private int count = 0;
private final Lock lock = new ReentrantLock();
public void increment() {
lock.lock();
try {
count++;
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
ReentrantLockExample example = new ReentrantLockExample();
Runnable task = () -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
};
Thread thread1 = new Thread(task);
Thread thread2 = new Thread(task);
thread1.start();
thread2.start();
try {
thread1.join();
thread2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Final count: " + example.count);
}
}读写锁
读写锁允许多个线程同时读，但只允许一个线程写，从而提高并发性能。
package cn.juwatech.concurrency;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReadWriteLock;
public class ReadWriteLockExample {
private int count = 0;
private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
public void increment() {
rwLock.writeLock().lock();
try {
count++;
} finally {
rwLock.writeLock().unlock();
}
}
public int getCount() {
rwLock.readLock().lock();
try {
return count;
} finally {
rwLock.readLock().unlock();
}
}
public static void main(String[] args) {
ReadWriteLockExample example = new ReadWriteLockExample();
Runnable writeTask = () -> {
for (int i = 0; i < 1000; i++) {
example.increment();
}
};
Runnable readTask = () -> {
for (int i = 0; i < 1000; i++) {
System.out.println("Count: " + example.getCount());
}
};
Thread writer = new Thread(writeTask);
Thread reader = new Thread(readTask);
writer.start();
reader.start();
try {
writer.join();
reader.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}5. 并发工具类
Java还提供了一些便捷的并发工具类，如CountDownLatch、CyclicBarrier和Semaphore等。
CountDownLatch
CountDownLatch允许一个或多个线程等待其他线程完成操作。
package cn.juwatech.concurrency;
import java.util.concurrent.CountDownLatch;
public class CountDownLatchExample {
public static void main(String[] args) throws InterruptedException {
int threadCount = 3;
CountDownLatch latch = new CountDownLatch(threadCount);
Runnable task = () -> {
System.out.println("Thread " + Thread.currentThread().getId() + " is running");
latch.countDown();
};
for (int i = 0; i < threadCount; i++) {
new Thread(task).start();
}
latch.await();
System.out.println("All threads have finished");
}
}CyclicBarrier
CyclicBarrier允许一组线程相互等待，直到到达一个共同的屏障点。
package cn.juwatech.concurrency;
import java.util.concurrent.CyclicBarrier;
public class CyclicBarrierExample {
public static void main(String[] args) {
int threadCount = 3;
CyclicBarrier barrier = new CyclicBarrier(threadCount, () -> {
System.out.println("All threads have reached the barrier");
});
Runnable task = () -> {
try {
System.out.println("Thread " + Thread.currentThread().getId() + " is waiting at the barrier");
barrier.await();
System.out.println("Thread " + Thread.currentThread().getId() + " has crossed the barrier");
} catch (Exception e) {
e.printStackTrace();
}
};
for (int i = 0; i < threadCount; i++) {
new Thread(task).start();
}
}
}Semaphore
Semaphore用于控制对资源的访问，允许多个线程同时访问特定数量的资源。
package cn.juwatech.concurrency;
import java.util.concurrent.Semaphore;
public class SemaphoreExample {
public static void main(String[] args) {
int permits = 3;
Semaphore semaphore = new Semaphore(permits);
Runnable task = () -> {
try {
semaphore.acquire();
System.out.println("Thread " + Thread.currentThread().getId() + " is accessing the resource");
Thread.sleep(1000); // 模拟资源访问
semaphore.release();
System.out.println("Thread "
+ Thread.currentThread().getId() + " has released the resource");
} catch (InterruptedException e) {
e.printStackTrace();
}
};
for (int i = 0; i < 10; i++) {
new Thread(task).start();
}
}
}通过以上内容，我们详细介绍了Java中高并发编程的基本概念及其实现方法，包括线程、线程池、并发集合、锁机制和并发工具类的使用。通过这些示例代码，大家可以更好地理解和应用Java的并发编程技术。
