转：JGroups 简介、适用场合、配置、程序例子Demo等完全使用指南

目前项目中在克服JGroups初期使用的困难之后，已经使用比较稳定了。感觉比较烦琐和容易出错的还是JGroups配置。感觉中文的资源较少，现将自己总结的经验总结如下
Tim http://hi.baidu.com/jabber/blog/item/7e879852a23efd0f0cf3e3ea.html

JGroups 适合使用场合
服务器集群cluster、多服务器通讯、服务器replication(复制)等，分布式cache缓存

JGroups 简介
JGroups是一个基于Java语言的提供可靠多播(组播)的开发工具包。在IP Multicast基础上提供可靠服务，也可以构建在TCP或者WAN上。主要是由Bela Ban开发，属于JBoss.org，在JBoss的网站也有一些相关文档。目前在 SourceForge上还是比较活跃，经常保持更新。

JGroups 配置

PING: 发现初始成员
MERGE2: 将网络层切分的包重新合并。
FD_SOCK: Failure Dectection 错误检测，基于TCP
FD：Failure Dectection 错误检测，基于心跳
VERIFY_SUSPECT: 检查貌似失败的节点
pbcast.NAKACK: 应答，提供可靠传输
UNICAST: 可靠的UNICAST
pbcast.STABLE: 计算广播信息是否稳定
VIEW_SYNC: 定期广播view(成员名单)
pbcast.GMS: Group membership, 处理joins/leaves/crashes等
FC: 流量控制
FRAG2:Fragmentation layer，分包，将大的数据包分拆成适合网络层传输

以上一些是比较重要的配置，基本上不能少。如果要深入研究可以在　org.jgroups.protocols　里面查看源代码

JGroups使用例子, JGroups demo, Tim的hello world例子
Timreceiver.java

import org.jgroups.tests.perf.Receiver;
import org.jgroups.tests.perf.Transport;
import org.jgroups.util.Util;

public class TimReceiver implements Receiver {
      private Transport transport = null;
      
      public static void main(String[] args) {
            TimReceiver t = new TimReceiver();
            try {
                  int sendMsgCount = 5000;
                  int msgSize = 1000;
                  t.start();

                  t.sendMessages(sendMsgCount, msgSize);
                  System.out.println("########## Begin to recv...");
                  Thread.currentThread().join();
            } catch (Exception e) {
                  e.printStackTrace();
            } finally {
                  if (t != null) {
                        t.stop();
                  }
            }
      }
      
      public void start()
                  throws Exception {
            transport = (Transport) new TimTransport();
            transport.create(null);
            transport.setReceiver(this);
            transport.start();
      }

      public void stop() {
            if (transport != null) {
                  transport.stop();
                  transport.destroy();
            }
      }

      private int count = 0;
      public void receive(Object sender, byte[] data) {
            System.out.print(".");
            if (++count == 5000) {
                  System.out.println("\r\nRECV DONE.");
                  System.exit(0);
            }
            
      }

      private void sendMessages(int count, int msgSize)
                  throws Exception {
            byte[] buf = new byte[msgSize];
            for (int k = 0; k < msgSize; k++)
                  buf[k] = 'T';

            System.out.println("-- sending " + count + " " + Util.printBytes(msgSize) + " messages");

            for (int i = 0; i < count; i++) {
                  transport.send(null, buf);
            }
            
            System.out.println("######### send complete");
      }
}

TimTransport.java

import java.util.Map;
import java.util.Properties;

import org.jgroups.Address;
import org.jgroups.JChannel;
import org.jgroups.Message;
import org.jgroups.ReceiverAdapter;
import org.jgroups.tests.perf.Receiver;
import org.jgroups.tests.perf.Transport;

public class TimTransport extends ReceiverAdapter implements Transport{
      private JChannel channel = null;
      private String groupName = "TimDemo";
      private Receiver receiver = null;
      
      String PROTOCOL_STACK_UDP1 = "UDP(bind_addr=192.168.100.59";  
      String PROTOCOL_STACK_UDP2 = ";mcast_port=8888";
      String PROTOCOL_STACK_UDP3 = ";mcast_addr=225.1.1.1";
      String PROTOCOL_STACK_UDP4 = ";tos=8;loopback=false;max_bundle_size=64000;" +
                  "use_incoming_packet_handler=true;use_outgoing_packet_handler=false;ip_ttl=2;enable_bundling=true):"
           + "PING:MERGE2:FD_SOCK:FD:VERIFY_SUSPECT:"
             +"pbcast.NAKACK(gc_lag=50;max_xmit_size=50000;use_mcast_xmit=false;" +
                         "retransmit_timeout=300,600,1200,2400,4800;discard_delivered_msgs=true):"
             +"UNICAST:pbcast.STABLE:VIEW_SYNC:"
             +"pbcast.GMS(print_local_addr=false;join_timeout=3000;" +
                         "join_retry_timeout=2000;" +
                         "shun=true;view_bundling=true):"
             +"FC(max_credits=2000000;min_threshold=0.10):FRAG2(frag_size=50000)";

            
      public Object getLocalAddress() {
            return channel != null ? channel.getLocalAddress() : null;
      }

      public void start() throws Exception {
            channel.connect(groupName);            
      }

      public void stop() {
            if (channel != null) {
                  channel.shutdown();
            }
      }

      public void destroy() {
            if (channel != null) {
                  channel.close();
                  channel = null;
            }
      }

      public void setReceiver(Receiver r) {
            this.receiver = r;
      }

      public Map dumpStats() {
            return channel != null ? channel.dumpStats() : null;
      }

      public void send(Object destination, byte[] payload) throws Exception {
            byte[] tmp = new byte[payload.length];
            System.arraycopy(payload, 0, tmp, 0, payload.length);
            Message msg = null;
            msg = new Message((Address) destination, null, tmp);
            if (channel != null) {
                  channel.send(msg);
            }
      }

      public void receive(Message msg) {
            Address sender = msg.getSrc();
            byte[] payload = msg.getBuffer();
            if (receiver != null) {
                  try {
                        receiver.receive(sender, payload);
                  } catch (Throwable tt) {
                        tt.printStackTrace();
                  }
            }
      }

      public void create(Properties config) throws Exception {
            String PROTOCOL_STACK = PROTOCOL_STACK_UDP1 + PROTOCOL_STACK_UDP2 + PROTOCOL_STACK_UDP3 + PROTOCOL_STACK_UDP4;
            channel = new JChannel(PROTOCOL_STACK);
            channel.setReceiver(this);            
      }

      public void send(Object destination, byte[] payload, boolean oob) throws Exception {
            send(destination, payload);
      }
}

JGroups 下载 download
http://www.jgroups.org/