JDK5原子变量实践――Ejb调用自动重连

1. ConnectorStatusPair类，需要同步两个状态，一个是进入连接队列线程数，一个是连接时间。目的是同一时间只有一个线程在重连，间隔一定时间只重连一次。
   
   import java.util.concurrent.atomic.AtomicReference;
   
   public class ConnectorStatusPair {
   
       private static class Pair {
   
           final int qLength;
           final long timeStamp;
   
           public Pair(int qLength, long timeStamp) {
               this.qLength = qLength;
               this.timeStamp = timeStamp;
           }
       }
       private AtomicReference<Pair> values;
   
       public ConnectorStatusPair(int qLength, long timeStamp) {
           values = new AtomicReference<Pair>(new Pair(qLength, timeStamp));
       }
      
       public int getQLength() {
           return values.get().qLength;
       }
   
       public long getTimeStamp() {
           return values.get().timeStamp;
       }
   
       /**
        * 原子操作加1
        * @return 更新后的值
        */
       public int incrementAndGetQLength() {
           while (true) {
               Pair oldv = values.get();
               Pair newv = new Pair(oldv.qLength + 1, oldv.timeStamp);
               if (values.compareAndSet(oldv, newv)) {
                   return newv.qLength;
               }
           }
       }
   
       /**
        * 原子操作减一
        * @return 更新后的值
        */
       public int decrementAndGetQLength() {
           while (true) {
               Pair oldv = values.get();
               Pair newv = new Pair(oldv.qLength - 1, oldv.timeStamp);
               if (values.compareAndSet(oldv, newv)) {
                   return newv.qLength;
               }
           }
       }
   
       /**
        * 原子操作比较当前时间减去values保存的时间是否大于给定的时间间隔，以毫秒计，如果为真则更新values保存的时间为当前时间
        * @param reconnectTimePeriod
        * @return 如果当前时间减去values保存的时间大于给定的时间间隔返回真，否则返回非真
        */
       public boolean compareAndSetTimeStamp(int reconnectTimePeriod) {
           while (true) {
               Pair oldv = values.get();
               long time = System.currentTimeMillis();
               if ((time - oldv.timeStamp) < reconnectTimePeriod) {
                   return false;
               }
               Pair newv = new Pair(oldv.qLength, time);
               if (values.compareAndSet(oldv, newv)) {
                   return true;
               }
           }
       }
   }
   
   
2. Ejb3ClientProxy类，调用ejb方法，支持自动重连同步
   
   import com.xued.clusteredejb.ExRemote;
   import java.util.Properties ;
   import javax.naming.Context;
   import javax.naming.InitialContext ;
   import javax.naming.NamingException;
   import org.jboss.remoting.CannotConnectException ;
   
   public class Ejb3ClientProxy {
   
       private ExRemote exBean;
       private Context ctx;
       private ConnectorStatusPair connectorStatus = new ConnectorStatusPair(0, 0);
   
       public Ejb3ClientProxy(String hostUrl) {
           try {
               Properties props = new Properties();
               props.put("java.naming.factory.initial", "org.jnp.interfaces.NamingContextFactory");
               props.put("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces");
               props.put("java.naming.provider.url", hostUrl);
               props.put("jnp.socketFactory", "org.jnp.interfaces.TimedSocketFactory ");
               props.put("jnp.timeout", "10000");
               props.put("jnp.sotimeout", "10000");
               this.ctx = new InitialContext(props);
               getExBeanInstance();
           } catch (NamingException ex) {
               System.out.println("EJB3 client initialize failed!");
           }
       }
   
       public String invoke(String name) {
           if (connectorStatus.getQLength() != 0) {
               return "not alive";
           }
           String res = null;
           try {
               res = exBean.invoke(name);
           } catch (CannotConnectException ex) {
               if (isNeedReconnect()) {
                   res = refreshConnection(name);
               } else {
                   res =  ex.getClass().getName() + ": " + ex.getMessage();
               }
               connectorStatus.decrementAndGetQLength ();
           } catch (Exception ex) {
               res = ex.getClass ().getName() + ": " + ex.getMessage();
           }
           return res;
       }
   
       private boolean isNeedReconnect(){
           return connectorStatus.incrementAndGetQLength() == 1 &&
                   connectorStatus.compareAndSetTimeStamp(60000); //间隔60秒重连一次
       }
      
      
       private void getExBeanInstance() throws NamingException {
           this.exBean = (ExRemote) this.ctx.lookup("ExBean/remote");
       }
   
       private String refreshConnection(String name) {
           String res;
           try {
               getExBeanInstance();
               res = exBean.invoke(name+" Server was crashed");
           } catch (NamingException ex1) {
               System.out.println("reconnect failed");
               res = "error occured";
           }
           return res;
       }
   }