Redis: Jedis 源代码剖析2- 发布者/订阅者模式剖析

在Jedis提供的发布者/订阅者模式中,最重要的就是JedisPubSub . 当订阅通道后,JedisPubSub就会轮询通道。直到通道取消订阅，才会继续执行。

因为Jedis是单线程,所以当订阅之后,线程就在循环。除非,在JedisPubSub收到消息后,新开线程继续执行任务。

在JedisPubSub 类中定义了接受消息后触发事件和轮询代码。JedisPubSub类是抽象类,所以为了实现自己的功能，必须继承该类。

public abstract class JedisPubSub {  private int subscribedChannels = 0;  private volatile Client client;  public void onMessage(String channel, String message) {  }  public void onPMessage(String pattern, String channel, String message) {  }  public void onSubscribe(String channel, int subscribedChannels) {  }  public void onUnsubscribe(String channel, int subscribedChannels) {  }  public void onPUnsubscribe(String pattern, int subscribedChannels) {  }  public void onPSubscribe(String pattern, int subscribedChannels) {  }  public void unsubscribe() {    if (client == null) {      throw new JedisConnectionException("JedisPubSub was not subscribed to a Jedis instance.");    }    client.unsubscribe();    client.flush();  }  public void unsubscribe(String... channels) {    if (client == null) {      throw new JedisConnectionException("JedisPubSub is not subscribed to a Jedis instance.");    }    client.unsubscribe(channels);    client.flush();  }  public void subscribe(String... channels) {    if (client == null) {      throw new JedisConnectionException("JedisPubSub is not subscribed to a Jedis instance.");    }    client.subscribe(channels);    client.flush();  }  public void psubscribe(String... patterns) {    if (client == null) {      throw new JedisConnectionException("JedisPubSub is not subscribed to a Jedis instance.");    }    client.psubscribe(patterns);    client.flush();  }  public void punsubscribe() {    if (client == null) {      throw new JedisConnectionException("JedisPubSub is not subscribed to a Jedis instance.");    }    client.punsubscribe();    client.flush();  }  public void punsubscribe(String... patterns) {    if (client == null) {      throw new JedisConnectionException("JedisPubSub is not subscribed to a Jedis instance.");    }    client.punsubscribe(patterns);    client.flush();  }  public boolean isSubscribed() {    return subscribedChannels > 0;  }  public void proceedWithPatterns(Client client, String... patterns) {    this.client = client;    client.psubscribe(patterns);    client.flush();    process(client);  }  public void proceed(Client client, String... channels) {    this.client = client;    client.subscribe(channels);    client.flush();    process(client);  }  //JedisPubSub执行一直轮询,直到取消订阅。  private void process(Client client) {    do {      List<Object> reply = client.getRawObjectMultiBulkReply();      final Object firstObj = reply.get(0);      if (!(firstObj instanceof byte[])) {        throw new JedisException("Unknown message type: " + firstObj);      }      final byte[] resp = (byte[]) firstObj;      if (Arrays.equals(SUBSCRIBE.raw, resp)) {        subscribedChannels = ((Long) reply.get(2)).intValue();        final byte[] bchannel = (byte[]) reply.get(1);        final String strchannel = (bchannel == null) ? null : SafeEncoder.encode(bchannel);        onSubscribe(strchannel, subscribedChannels);      } else if (Arrays.equals(UNSUBSCRIBE.raw, resp)) {        subscribedChannels = ((Long) reply.get(2)).intValue();        final byte[] bchannel = (byte[]) reply.get(1);        final String strchannel = (bchannel == null) ? null : SafeEncoder.encode(bchannel);        onUnsubscribe(strchannel, subscribedChannels);      } else if (Arrays.equals(MESSAGE.raw, resp)) {        final byte[] bchannel = (byte[]) reply.get(1);        final byte[] bmesg = (byte[]) reply.get(2);        final String strchannel = (bchannel == null) ? null : SafeEncoder.encode(bchannel);        final String strmesg = (bmesg == null) ? null : SafeEncoder.encode(bmesg);        onMessage(strchannel, strmesg);      } else if (Arrays.equals(PMESSAGE.raw, resp)) {        final byte[] bpattern = (byte[]) reply.get(1);        final byte[] bchannel = (byte[]) reply.get(2);        final byte[] bmesg = (byte[]) reply.get(3);        final String strpattern = (bpattern == null) ? null : SafeEncoder.encode(bpattern);        final String strchannel = (bchannel == null) ? null : SafeEncoder.encode(bchannel);        final String strmesg = (bmesg == null) ? null : SafeEncoder.encode(bmesg);        onPMessage(strpattern, strchannel, strmesg);      } else if (Arrays.equals(PSUBSCRIBE.raw, resp)) {        subscribedChannels = ((Long) reply.get(2)).intValue();        final byte[] bpattern = (byte[]) reply.get(1);        final String strpattern = (bpattern == null) ? null : SafeEncoder.encode(bpattern);        onPSubscribe(strpattern, subscribedChannels);      } else if (Arrays.equals(PUNSUBSCRIBE.raw, resp)) {        subscribedChannels = ((Long) reply.get(2)).intValue();        final byte[] bpattern = (byte[]) reply.get(1);        final String strpattern = (bpattern == null) ? null : SafeEncoder.encode(bpattern);        onPUnsubscribe(strpattern, subscribedChannels);      } else {        throw new JedisException("Unknown message type: " + firstObj);      }    } while (isSubscribed());    /* Invalidate instance since this thread is no longer listening */    this.client = null;  }  public int getSubscribedChannels() {    return subscribedChannels;  }}

/** * Note that subscribe is a blocking operation because it will poll Redis for responses on the thread that calls subscribe. *  A single JedisPubSub instance can be used to subscribe to multiple channels. * You can call subscribe or psubscribe on an existing JedisPubSub instance to change your subscriptions. * @author Administrator * */public class JedisPubSubListener extends JedisPubSub{@Overridepublic void onMessage(String channel, String message) {super.onMessage(channel, message);System.out.println("onMessage");}@Overridepublic void onPMessage(String pattern, String channel, String message) {// TODO Auto-generated method stubsuper.onPMessage(pattern, channel, message);System.out.println("onPMessage");}@Overridepublic void onSubscribe(String channel, int subscribedChannels) {// TODO Auto-generated method stubsuper.onSubscribe(channel, subscribedChannels);System.out.println("onSubscribe");}@Overridepublic void onUnsubscribe(String channel, int subscribedChannels) {// TODO Auto-generated method stubsuper.onUnsubscribe(channel, subscribedChannels);System.out.println("onUnsubscribe");}@Overridepublic void onPUnsubscribe(String pattern, int subscribedChannels) {// TODO Auto-generated method stubsuper.onPUnsubscribe(pattern, subscribedChannels);System.out.println("onPUnsubscribe");}@Overridepublic void onPSubscribe(String pattern, int subscribedChannels) {// TODO Auto-generated method stubsuper.onPSubscribe(pattern, subscribedChannels);System.out.println("onPSubscribe");}}

TestPub 为测试类,一直发布消息：

public class TestPub {public static void main(String[] args) {Jedis jedis = new Jedis();while (true) {              try {Thread.sleep(1000);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}             jedis.publish("channel", "Pub_Message");}}}

TestSub消息进行订阅：

public class TestSub {
public static void main(String[] args)
{
Jedis jedis =new Jedis();
//创建一个订阅者
JedisPubSub listener =new JedisPubSubListener();

//订阅指定通道
jedis.subscribe(listener, "channel");

System.out.println("===subscribe success==");
}
}