让已有的系统开放RMI服务(1)

1.本来trigger receiver流程的模块和接收者类是放在一个APP Server上的，但由于性能的考虑，这种schedule模块的调度和管理可能会影响业务逻辑的执行，占用业务逻辑执行的系统资源，所以将它放到单独的JVM上运行，作为一个Standalone的java application。这样schedule模块就不能直接通过内存调用接收者流程，接收者必须开放远程rpc服务，让trigger通过远程调用的方法主动调用消息接收者去接受消息。

原来的系统通过MessageReceiverFactory获得一个MessageReceiver 然后主动接收消息。

 

 

 

MessageReceiver:

public interface MessageReceiver {

      void invokeProcessFlow(String processId) throws ServerReceiverException;

}

 

ServerMessageReceiver:

 

public class ServerMessageReceiver implements MessageReceiver {  

      ServerMessageReceiver() {

 

      }

      public void invokeProcessFlow(String processId) throws ServerReceiverException {

        //receive message

}

 

 

 

 

MessageReceiverFactory:

 

public class MessageReceiverFactory {

      private static MessageReceiver messageReceiver;

 

      private static void init() throws ServerReceiverException {

            messageReceiver = new ServerMessageReceiver();

      }

 

 

      public synchronized static MessageReceiver getMessageReceiver() throws ServerReceiverException {

            if(messageReceiver == null) {

                  init();

            }

            return messageReceiver;

      }

     

}

 

2.增加RMI服务后：

 

客户端：

·         客户端通过MessageReceiverFactory获得MessageReceiver的远程版本：RemoteMessageReceiver

·         客户端使用远程版本的MessageReceiver  look up出RemotableMessageReceiver的RMI Stub进行远程的RPC调用，通知服务器端接收消息。

 

public class RemoteMessageReceiver implements MessageReceiver {

      private RemotableMessageReceiver messageReceiver;

      private String rmiHost;

      private int rmiPort;

      private String serviceName;

 

    public RemoteMessageReceiver(String host, int port, String serviceName) throws ServerReceiverException {

      try{

            this.rmiHost = host;

            this.rmiPort = port;

            this.serviceName = serviceName;

            Registry registry = LocateRegistry.getRegistry(rmiHost, rmiPort);

            messageReceiver = (RemotableMessageReceiver) registry.lookup(this.serviceName);

      }catch(Exception ex) {

            throw new ServerReceiverException("look up remote message receiver failed!", this, ex);

      }

     

      }

 

      public void invokeProcessFlow(String processId) throws ServerReceiverException {

            try {

                  this.messageReceiver.invokeProcessFlow(processId);

            } catch (RemoteException e) {

                  throw new ServerReceiverException(e.getMessage(), this, e);

            }

      }

}

 

这里用了适配器模式，对RemotableMessageReceiver进行适配，从而满足MessageReceiver接口的标准，方便MessageReceiverFactory的统一生产，并且使客户端使用的RemoteMessageReceiver和具体使用的通信方法解耦，将来如果不使用RMI, 只需要替换RemotableMessageReceiver就可以了。不会影响客户端的代码。

 

 

服务器端：

• 服务器端设置开关，可以开启和关闭远程服务。
• 如果开启远程服务，就需要注册服务，注册的服务对象是提供给客户端用的远程对象，服务端本身使用的MessageReceiver不需要实现RemotableMessageReceiver接口和原来一样实现MessageReceiver接口，从而原有的应用并没有太大影响。
• 服务器端通过MessageReceiverFactory获得MessageReceiver也可以主动接受消息，如果需要提供远程服务，就必须注册远程服务。

 

这样，服务器端首先增加了RemotableMessageReceiver接口，所有远程对象实现该接口，RMIMessageReceiver提供RMI服务的远程对象，供客户端远程调用。RMIMessageReceiver必须满足RemotableMessageReceiver接口的契约，所以也使用了适配器模式。增加了RMIMessageReceiver后，服务器端使用的MessageReceiver就和RMIMessageReceiver耦合在一起了，为了解耦，我又新增了一个StdMessageReceiver类，作为服务器端本地的MessageReceiver，供服务器端本地调用，StdMessageReceiver用了装饰器模式，对已有的MessageReceiver进行修饰，支持服务器端本地调用，如果以后本地调用加了新的功能就不会影响RMIMessageReceiver的功能了，比如凡是本地调用都需要在服务器端记log，这样就只需要在StdMessageReceiver添加打log的功能，而不会影响RMIMessageReceiver。

 

MessageReceiverFactory简单工厂用于生产MessageReceiver对象，可能是客户端的RemoteMessageReceiver也可能是服务器端的StdMessageReceiver。

 

为了在deploy时候就启动RMI服务，我们可以在servlet的init方法中初始化并注册RMI服务，在deetroy方法中相应的取消RMI服务。

 

RemotableMessageReceiver: 远程服务对象接口

public interface RemotableMessageReceiver extends Remote {

      void invokeProcessFlow(String processId) throws ServerReceiverException,

                  RemoteException;

}

 

 

 

RMIMessageReceiver：提供RMI服务的远程对象

public class RMIMessageReceiver implements RemotableMessageReceiver {

      private MessageReceiver messageReceiver;

 

      RMIMessageReceiver(MessageReceiver messageReceiver) throws RemoteException {

            this.messageReceiver = messageReceiver;

            SystemInfo sysInfo = ContextFactory.getSystemConfigContext().getSystemInfo();

            System.out.println("beign to bind at rmiport: " + sysInfo.getRmiport());

            RMIUtils.bind(sysInfo.getRmiport(), sysInfo

                        .getReceiverRmiBindName(), this);

      }

 

      public void invokeProcessFlow(String processId)

                  throws ServerReceiverException, RemoteException {

            this.messageReceiver.invokeProcessFlow(processId);

      }

 

}

 

SystemInfo存储的是一些配置信息，比如是不是服务器端，是不是需要开启远程服务，如果开启的话相应的host，port和rmi远程对象绑定的服务名

 

StdMessageReceiver：服务器端使用的MessageReceiver。

public class StdMessageReceiver implements MessageReceiver {

      private MessageReceiver messageReceiver;

 

      public StdMessageReceiver(MessageReceiver messageReceiver) {

            this.messageReceiver = messageReceiver;

      }

 

      public void invokeProcessFlow(String processId) throws ServerReceiverException {

            //do some log

            this.messageReceiver.invokeProcessFlow(processId);

      }

}