用户锁，扣费模型，足够能支持一般并发

足够能支持一般并发，高并发可在这基础上使用redis原子性

UserPrice.java

package com.andnnl.userlock;import java.util.Map;import java.util.concurrent.ConcurrentHashMap;/** * Created by andnnl on 2017/7/31. */public class UserPrice {    private static UserPrice instance;    private static Map<String, byte[]> lockMap = new ConcurrentHashMap<>();    private static Map<String, User> userMap = new ConcurrentHashMap<>();    private UserPrice() {    }    public synchronized static UserPrice getInstance(String uid) {        if (instance == null)            instance = new UserPrice();        byte[] b = lockMap.get(uid);        if (b == null) {            lockMap.put(uid, new byte[]{});        }        return instance;    }    public boolean checkPrice(String uid, int price) {        synchronized (lockMap.get(uid)) {            User user = userMap.get(uid);            if (user == null) {                user = new User(uid, 100000000);                userMap.put(uid, user);            }            if (user.price - price >= 0) {                return true;            }        }        return false;    }    public boolean deduct(String uid, int price) {        synchronized (lockMap.get(uid)) {            if (checkPrice(uid, price)) {                User user = userMap.get(uid);                user.price -= price;            }        }        return false;    }    static void print() {        for (Map.Entry<String, User> entry : userMap.entrySet()) {            System.out.println(entry.getValue().toString());        }    }    public static void main(String[] args) {        for (int i = 0; i < 300; i++) {            final int finalI = i % 3;            new Thread(new Runnable() {                @Override                public void run() {                    String uid = "uid" + finalI;                    UserPrice up = UserPrice.getInstance(uid);                    while (true) {                        if (up.checkPrice(uid, 3)) {                            up.deduct(uid, 3);                        }                    }                }            }).start();        }        while (true) {            try {                Thread.currentThread().sleep(1000);            } catch (InterruptedException e) {                e.printStackTrace();            }            print();            System.out.println();        }    }}

User.java

package com.andnnl.userlock;/** * Created by andnnl on 2017/7/31. */public class User {    String uid;    int price;    public User() {    }    public User(String uid, int price) {        this.uid = uid;        this.price = price;    }    public String getUid() {        return uid;    }    public void setUid(String uid) {        this.uid = uid;    }    public int getPrice() {        return price;    }    public void setPrice(int price) {        this.price = price;    }    @Override    public String toString() {        return "User{" +                "uid='" + uid + '\'' +                ", price=" + price +                '}';    }}