单例模式

单例模式使用特点：

        1、保证系统从启动到停止，只能产生一个实例。

        2、应用中遇到冲突的时候，即产生了两个实例会有问题的时候。

以下是单例模式的实现方式：

package demo.lihongmin.singleton;// 饿汉式 单例模式public class Singleton1 {// 构造私有private Singleton1(){}// 声明一个静态变量保存单利的引用private static final Singleton1 single = new Singleton1();// 通过静态方法获取单利的引用public static Singleton1 getInstance(){return single;}}

package demo.netty_lihongmin.singleton;// 懒汉式单例模式，保证线程安全public class Singleton2 {// 构造私有private Singleton2(){}// 声明一个静态变量保存单利的引用private static Singleton2 single = null;// 通过静态方法获取单利的引用，并保证线程的安全public static synchronized Singleton2 getInstance(){if(single == null) {single = new Singleton2();}return single;}}

package demo.netty_lihongmin.singleton;// 懒汉式单例模式，保证线程安全public class Singleton3 {// 构造私有private Singleton3(){}// 声明一个静态变量保存单利的引用private static Singleton3 single = null;// 通过静态方法获取单利的引用，并保证线程的安全使用双重锁检查public static Singleton3 getInstance(){if(single == null) {synchronized(Singleton3.class){if(single == null) {single = new Singleton3();}}}return single;}}

package demo.netty_lihongmin.singleton;/** *  内部类的单例模式 *  注意点： 内部类的初始化需要依赖主类 */public class Singleton4 {// 构造私有private Singleton4(){}// 声明一个静态内部类private static class InnerClass {// final 是防止内部类将这个属性进行覆盖private static final Singleton4 INSTANCE = new Singleton4();}// final 是防止子类从写父类的方法public static final Singleton4 getInstance(){return InnerClass.INSTANCE;}}

package demo.netty_lihongmin.singleton;public class Singleton5 {String name = null;// 构造私有private Singleton5(){}// 使用volatile关键字private static volatile Singleton5 instance = null; // final 是防止子类从写父类的方法public static Singleton5 getInstance(){if(instance == null) {synchronized(Singleton5.class) {if(instance == null) {instance = new Singleton5();}}}return instance;}}

package demo.netty_lihongmin.singleton;public enum Singleton6 {INSTANCE;// 构造私有private Singleton6(){}}

package demo.netty_lihongmin.singleton;import java.util.Map;import java.util.concurrent.ConcurrentHashMap;// spring方式public class Singleton7 {private static Map<String,Singleton7> map = new ConcurrentHashMap<String,Singleton7>();static{Singleton7 single = new Singleton7();map.put(single.getClass().getName(), single);}// 构造私有private Singleton7(){}public static Singleton7 getInstance(String name){if(name ==null) {name = Singleton7.class.getName();}if(map.get(name) == null) {try{map.put(name, (Singleton7)Class.forName(name).newInstance());} catch (InstantiationException e){e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}}return map.get(name);}}

package demo.netty_lihongmin.singleton;import java.util.concurrent.CountDownLatch;public class SingletonTest {public static void main(String[] args) {int count = 100;CountDownLatch latch = new CountDownLatch(count);for(int i=0 ; i<count ; i++) {new Thread(){public void run() {System.out.println(System.currentTimeMillis()+" "+ Singleton4.getInstance());};}.start();}try {latch.await();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}