Hazelcast 内存数据网格

Hazelcast ( www.hazelcast.com)是一种内存数据网格 in-memory data grid，提供Java程序员关键任务交易和万亿级内存应用。

Hazelcast的集群属于“无主节点”，这意味着它不是一个客户端 - 服务器系统。有一个集群的领导者，默认是最老的成员，管理数据是如何在系统间分布，但是，如果该节点当机，那么是下面一个旧的节点接管。

你所用的数据结构Maps List和队列都是保存在内存中。如果集群中的一个节点死亡，数据不会丢失，但如果多个节点同时当机，那么你就麻烦了。

下面以BigWideWorl为案例说明Hazelcast的使用，首先依赖包导入：

<dependency>
<groupId>com.hazelcast</groupId>
<artifactId>hazelcast</artifactId>
<version>3.1</version>
</dependency>

public class BigWideWorld {
      

  private static Random rand = new Random(System.currentTimeMillis());
      

  private final Users users = new Users();
      

  private final int totalNumUsers = users.size();
      

  public String nextUser() {
      

    User user = users.get(rand.nextInt(totalNumUsers)); 

    String name = user.getUsername();       

    return name;       

  }       

}

nextUser()方法可以随机获得一个用户的名称，用户集合由Users类管理。

public class Users {

/** The users in the database */ 
  private final User[] users = { new User("fred123", "Fred", "Jones", "fredj@a.com"), 
      new User("jim", "Jim", "Jones", "jimj@a.com"), 
      new User("bill", "Bill", "Jones", "bill@a.com"), 
      new User("ted111", "Edward", "Jones", "tedj@a.com"), 
      new User("annie", "Annette", "Jones", "annj@a.com"), 
      new User("lucy", "Lucy", "Jones", "lucyj@a.com"), 
      new User("jimj", "James", "Jones", "jimj@a.com"), 
      new User("jez", "Jerry", "Jones", "fredj@a.com"), 
      new User("will", "William", "Jones", "willj@a.com"), 
      new User("shaz", "Sharon", "Jones", "shazj@a.com"), 
      new User("paula", "Paula", "Jones", "pauj@a.com"), 
      new User("leo", "Leonardo", "Jones", "leoj@a.com"), };

private final Map<String, User> userMap;

public Users() {

userMap = new HashMap<String, User>();

for (User user : users) { 
      userMap.put(user.getUsername(), user); 
    } 
  }

/** 
   * The number of users in the database 
   */ 
  public int size() { 
    return userMap.size(); 
  }

/** 
   * Given a number, return the user 
   */ 
  public User get(int index) { 
    return users[index]; 
  }

/** 
   * Given the user's name return the User details 
   */ 
  public User get(String username) { 
    return userMap.get(username); 
  }

/** 
   * Return the user names. 
   */ 
  public Set<String> getUserNames() { 
    return userMap.keySet(); 
  } 
}

Users其实类似一个Map集合。下面是用户类：

public class User implements Serializable {

private static final long serialVersionUID = 1L; 
  private final String username; 
  private final String firstName; 
  private final String lastName; 
  private final String email;

public User(String username, String firstName, String lastName, String email) { 
    super(); 
    this.username = username; 
    this.firstName = firstName; 
    this.lastName = lastName; 
    this.email = email; 
  }

public String getUsername() { 
    return username; 
  }

public String getFirstName() { 
    return firstName; 
  }

public String getLastName() { 
    return lastName; 
  }

public String getEmail() { 
    return email; 
  }

@Override 
  public String toString() {

StringBuilder sb = new StringBuilder("User: "); 
    sb.append(username); 
    sb.append(" "); 
    sb.append(firstName); 
    sb.append(" "); 
    sb.append(lastName); 
    sb.append(" "); 
    sb.append(email);

return sb.toString(); 
  } 
}

用户User必须实现序列化接口。

客户端调用代码如下：

public class Main {

public static void main(String[] args) throws InterruptedException {

BigWideWorld theWorld = new BigWideWorld();

MyApplication application = new MyApplication();

while (true) {

String username = theWorld.nextUser();

if (application.isLoggedOn(username)) { 
        application.logout(username); 
      } else { 
        application.logon(username); 
      }

application.displayUsers(); 
      TimeUnit.SECONDS.sleep(2); 
    } 
  }

}

此代码创建BigWideWorld和所有MyApplication的实例。然后，它无限循环抓住抓取下一个随机的用户名。如果是已经登录的用户，那么注销该用户。如果没有登录的用户，然后登录用户后显示。

运行该代码：

java -cp /your path to the/hazelcast-3.1/lib/hazelcast-1.jar:. com.captaindebug.hazelcast.gettingstarted.Main

得到如下结果：

Logged on users:
User: fred123 Fred Jones fredj@a.com
User: jimj James Jones jimj@a.com
User: shaz Sharon Jones shazj@a.com
User: paula Paula Jones pauj@a.com
User: lucy Lucy Jones lucyj@a.com
User: jez Jerry Jones fredj@a.com
User: jim Jim Jones jimj@a.com
7 -- 14:54:16-17

可以多开几个终端运行这个代码。

你会看到用户不断在登录推出，用户Map集合每次显示出改变，关键是：一个应用的Map大小变化会影响其他窗口应用内的大小，好像大家共用一个Users的Map集合。

发布者和订阅者实现

假设有一个模型：

public class StockPrice implements Serializable {

private static final long serialVersionUID = 1L;

private final BigDecimal bid;

private final BigDecimal ask;

private final String code;

private final String description;

private final long timestamp;

/** 
   * Create a StockPrice for the given stock at a given moment 
   */ 
  public StockPrice(BigDecimal bid, BigDecimal ask, String code, String description, 
      long timestamp) { 
    super(); 
    this.bid = bid; 
    this.ask = ask; 
    this.code = code; 
    this.description = description; 
    this.timestamp = timestamp; 
  }

public BigDecimal getBid() { 
    return bid; 
  }

public BigDecimal getAsk() { 
    return ask; 
  }

public String getCode() { 
    return code; 
  }

public String getDescription() { 
    return description; 
  }

public long getTimestamp() { 
    return timestamp; 
  }

@Override 
  public String toString() {

StringBuilder sb = new StringBuilder("Stock - "); 
    sb.append(code); 
    sb.append(" - "); 
    sb.append(description); 
    sb.append(" - "); 
    sb.append(description); 
    sb.append(" - Bid: "); 
    sb.append(bid); 
    sb.append(" - Ask: "); 
    sb.append(ask); 
    sb.append(" - "); 
    SimpleDateFormat df = new SimpleDateFormat("HH:MM:SS"); 
    sb.append(df.format(new Date(timestamp))); 
    return sb.toString(); 
  } 
}

要求将股票的买入卖出价格在任何时间发布给做市商。

发布者代码：

public class MarketMaker implements Runnable {

private static Random random = new Random();

private final String stockCode;

private final String description;

private final ITopic<StockPrice> topic;

private volatile boolean running;

public MarketMaker(String topicName, String stockCode, String description) { 
    this.stockCode = stockCode; 
    this.description = description; 
    this.topic = createTopic(topicName); 
    running = true; 
  }

@VisibleForTesting 
  ITopic<StockPrice> createTopic(String topicName) { 
    HazelcastInstance hzInstance = Hazelcast.newHazelcastInstance(); 
    return hzInstance.getTopic(topicName); 
  }

public void publishPrices() {

Thread thread = new Thread(this); 
    thread.start(); 
  }

@Override 
  public void run() {

do { 
      publish(); 
      sleep(); 
    } while (running); 
  }

private void publish() {

StockPrice price = createStockPrice(); 
    System.out.println(price.toString()); 
    topic.publish(price); 
  }

@VisibleForTesting 
  StockPrice createStockPrice() {

double price = createPrice(); 
    DecimalFormat df = new DecimalFormat("#.##");

BigDecimal bid = new BigDecimal(df.format(price - variance(price))); 
    BigDecimal ask = new BigDecimal(df.format(price + variance(price)));

StockPrice stockPrice = new StockPrice(bid, ask, stockCode, description, 
        System.currentTimeMillis()); 
    return stockPrice; 
  }

private double createPrice() {

int val = random.nextInt(2010 - 1520) + 1520; 
    double retVal = (double) val / 100; 
    return retVal; 
  }

private double variance(double price) { 
    return (price * 0.01); 
  }

private void sleep() { 
    try { 
      TimeUnit.SECONDS.sleep(2); 
    } catch (InterruptedException e) { 
      e.printStackTrace(); 
    } 
  }

public void stop() { 
    running = false; 
  }

public static void main(String[] args) throws InterruptedException {

MarketMaker bt = new MarketMaker("STOCKS", "BT.L", "British Telecom"); 
    MarketMaker cbry = new MarketMaker("STOCKS", "CBRY.L", "Cadburys"); 
    MarketMaker bp = new MarketMaker("STOCKS", "BP.L", "British Petrolium");

bt.publishPrices(); 
    cbry.publishPrices(); 
    bp.publishPrices();

}

}

其中代码关键是：

ITopic<StockPrice> createTopic(String topicName) { 
    HazelcastInstance hzInstance = Hazelcast.newHazelcastInstance(); 
    return hzInstance.getTopic(topicName); 
  }

这是设置Hazelcast，创建一个主题topic用于股票发布。真正发布是在run方法中的topic.publish(price);

订阅者代码如下：

public class Client implements MessageListener<StockPrice> {

public Client(String topicName) { 
    HazelcastInstance hzInstance = Hazelcast.newHazelcastInstance(); 
    ITopic<StockPrice> topic = hzInstance.getTopic(topicName); 
    topic.addMessageListener(this); 
  }

/** 
   * @see com.hazelcast.core.MessageListener#onMessage(com.hazelcast.core.Message) 
   */ 
  @Override 
  public void onMessage(Message<StockPrice> arg0) { 
    System.out.println("Received: " + arg0.getMessageObject().toString()); 
  }

public static void main(String[] args) {

new Client("STOCKS"); 
  }

}

下面是运行，需要配合两个包：hazel cast-3.1.jar and guava-13.0.1.jar.

java -cp ./:/Users/Roger/tmp/mm/guava-13.0.1.jar:/Users/Roger/tmp/mm/hazelcast-3.1.jar com.captaindebug.hazelcast.pubsub.MarketMaker

下面是订阅者运行：

java -cp ./:/Users/Roger/tmp/mm/guava-13.0.1.jar:/Users/Roger/tmp/mm/hazelcast-3.1.jar com.captaindebug.hazelcast.pubsub.Client