Java多线程编程中的线程池应用

在Java 5及更高版本中，`ThreadPoolExecutor`类被广泛用于线程池的管理，以提高应用程序的性能和资源利用率。线程池是实现多任务并行处理的有效手段，其核心思想是以空间换时间，即通过预先创建一定数量的线程，避免了频繁创建和销毁线程带来的开销。

### 线程池的创建方法

#### 方法1：固定大小的线程池
```java
public static void createThreadPoolMethod1(){
ExecutorService threadPool = Executors.newFixedThreadPool(4); // 创建一个固定大小为4的线程池
MyTask t1 = new MyTask();
MyTask t2 = new MyTask();
MyTask t3 = new MyTask();
MyTask t4 = new MyTask();
MyTask t5 = new MyTask();
threadPool.execute(t1);
threadPool.execute(t2);
threadPool.execute(t3);
threadPool.execute(t4);
threadPool.execute(t5);
threadPool.shutdown();
}
```

#### 方法2：可变大小的线程池
```java
public static void createThreadPoolMethod2(){
ThreadPoolExecutor threadPool = (ThreadPoolExecutor) Executors.newCachedThreadPool(); // 创建一个可变大小的线程池
MyTask t1 = new MyTask();
MyTask t2 = new MyTask();
MyTask t3 = new MyTask();
MyTask t4 = new MyTask();
MyTask t5 = new MyTask();
threadPool.execute(t1);
threadPool.execute(t2);
threadPool.execute(t3);
threadPool.execute(t4);
threadPool.execute(t5);
threadPool.shutdown();
}
```

#### 方法3：单线程线程池
```java
public static void createThreadPoolMethod3(){
ExecutorService threadPool = Executors.newSingleThreadExecutor(); // 创建一个单线程线程池
MyTask t1 = new MyTask();
MyTask t2 = new MyTask();
MyTask t3 = new MyTask();
MyTask t4 = new MyTask();
MyTask t5 = new MyTask();
threadPool.execute(t1);
threadPool.execute(t2);
threadPool.execute(t3);
threadPool.execute(t4);
threadPool.execute(t5);
threadPool.shutdown();
}
```

#### 方法4：定时任务线程池
```java
public static void createThreadPoolMethod4(){
ScheduledExecutorService threadPool = Executors.newScheduledThreadPool(4); // 创建一个支持定时任务的线程池
MyTask t3 = new MyTask();
MyTask t4 = new MyTask();
MyTask t5 = new MyTask();
threadPool.scheduleWithFixedDelay(t5, 10, 5, TimeUnit.SECONDS); // 延迟10秒后每隔5秒执行一次任务
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
threadPool.shutdown();
}
```

### 任务类定义
```java
static class MyTask implements Runnable {
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + "正在执行。。。" + new Date());
}
}
```

以上代码展示了如何在Java中使用不同的线程池配置来管理和调度多线程任务，每种线程池都有其特定的应用场景，选择合适的线程池类型可以显著提升程序的性能。