public class DependencyInjectionSingleton {

// 在 getBean 加锁后 这个地方有必要使用 ConcurrentHashMap 吗 private static final Map<String, Object> IOC = new HashMap<>();

private DependencyInjectionSingleton() { System.out.println("我实例化了"); }

// 方法这儿必须加锁，不然会实例多个 public static Object getBean(String name) { synchronized (IOC) { if (!IOC.containsKey(name)) { try { Object obj = Class.forName(name).newInstance(); IOC.put(name, obj); return obj; } catch (Exception e) { e.printStackTrace(); } } return IOC.get(name); } }

static class TestRun implements Runnable { @Override public void run() { System.out.println(Thread.currentThread().getName() + "---" + getBean("create.singleton.inject.DependencyInjectionSingleton")); } }

public static void main(String[] args) throws InterruptedException { long start = System.currentTimeMillis(); ThreadPoolExecutor executor = ThreadPool.getExecutor(); executor.execute(new TestRun()); executor.execute(new TestRun()); executor.execute(new TestRun()); executor.execute(new TestRun()); executor.execute(new TestRun()); executor.execute(new TestRun()); executor.shutdown(); Thread thread = new Thread(new TestRun()); thread.start(); thread.join(); long end = System.currentTimeMillis(); System.out.println("耗时--" + (end - start) + "ms"); }

}