Properties类和单例模型总结

1.Properties类

1.1包1.2类结构1.3配置文件1.4解析 2.设计模式-单例模型

2.1 什么是单例？2.2 懒汉模式的线程安全问题

2.3 线程安全解决方案 2.4 饿汉模式

java.util.Properties

public class Properties extends Hashtable

resources/user.properties

user.username = admin
user.password = 223

Properties prop = new Properties();

String path = Thread.currentThread().getContextClassLoader().getResource("").getPath();
String fileName = path+"com/dyit/resources/user.properties";
prop.load(new FileReader(fileName));
System.out.println("用户名: " + prop.getProperty("user.username"));
System.out.println("密码: " + prop.getProperty("user.password"));

创建型模式： 创建对象·

核心： 内存中只有唯一的一个对象

Executor pool = Executors.newCachedThreadPool();

		for (int i = 0; i < 10; i++) {
			pool.execute(() -> {
				for (int j = 0; j < 10; j++) {
					System.out.println(Thread.currentThread().getName() + ": " + Singleton.getIntance().hashCode());
					try {
						Thread.sleep(300);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			});
		}

pool-1-thread-6: 1335324870
pool-1-thread-10: 1335324870
pool-1-thread-1: 1967528551
pool-1-thread-8: 1335324870
pool-1-thread-4: 2087870959
pool-1-thread-9: 1335324870
pool-1-thread-7: 1335324870

ReentrantLock/synchronized

package com.dyit.singleton;

import java.util.concurrent.locks.ReentrantLock;

import javax.xml.crypto.dsig.keyinfo.RetrievalMethod;


public class Singleton {

	private static Singleton instance = null; // instance 一开始没有引用任何对象
	private final static ReentrantLock lock = new ReentrantLock();

	private Singleton() {

	}

	
	public static Singleton getIntance() {

		lock.lock();
		try {
			if (instance == null) {
				instance = new Singleton();
			}
		} finally {
			lock.unlock();
		}
		return instance;

	}

}

package com.dyit.singleton;


public class Singleton2 {
	
	private final static Singleton2 instance
	= new Singleton2();//JVM保证线程安全
	
	private Singleton2() {}
	
	
	public static Singleton2 getIntance() {
		return instance;
	}
}