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讓已有的系統開放RMI服務

1.本來trigger receiver流程的模塊和接收者類是放在一個APP Server上的，但由于性能的考慮，這種schedule模塊的調度和管理可能會影響業務邏輯的執行，占用業務邏輯執行的系統資源，所以將它放到單獨的JVM上運行，作為一個Standalone的java application。這樣schedule模塊就不能直接通過內存調用接收者流程，接收者必須開放遠程rpc服務，讓trigger通過遠程調用的方法主動調用消息接收者去接受消息。

原來的系統通過MessageReceiverFactory獲得一個MessageReceiver 然后主動接收消息。

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服務后：

客戶端：

· 客戶端通過MessageReceiverFactory獲得MessageReceiver的遠程版本：RemoteMessageReceiver

· 客戶端使用遠程版本的MessageReceiver look up出RemotableMessageReceiver的RMI Stub進行遠程的RPC調用，通知服務器端接收消息。

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);

}

這里用了適配器模式，對RemotableMessageReceiver進行適配，從而滿足MessageReceiver接口的標準，方便MessageReceiverFactory的統一生產，并且使客戶端使用的RemoteMessageReceiver和具體使用的通信方法解耦，將來如果不使用RMI, 只需要替換RemotableMessageReceiver就可以了。不會影響客戶端的代碼。

服務器端：

服務器端設置開關，可以開啟和關閉遠程服務。
如果開啟遠程服務，就需要注冊服務，注冊的服務對象是提供給客戶端用的遠程對象，服務端本身使用的MessageReceiver不需要實現RemotableMessageReceiver接口和原來一樣實現MessageReceiver接口，從而原有的應用并沒有太大影響。
服務器端通過MessageReceiverFactory獲得MessageReceiver也可以主動接受消息，如果需要提供遠程服務，就必須注冊遠程服務。

這樣，服務器端首先增加了RemotableMessageReceiver接口，所有遠程對象實現該接口，RMIMessageReceiver提供RMI服務的遠程對象，供客戶端遠程調用。RMIMessageReceiver必須滿足RemotableMessageReceiver接口的契約，所以也使用了適配器模式。增加了RMIMessageReceiver后，服務器端使用的MessageReceiver就和RMIMessageReceiver耦合在一起了，為了解耦，我又新增了一個StdMessageReceiver類，作為服務器端本地的MessageReceiver，供服務器端本地調用，StdMessageReceiver用了裝飾器模式，對已有的MessageReceiver進行修飾，支持服務器端本地調用，如果以后本地調用加了新的功能就不會影響RMIMessageReceiver的功能了，比如凡是本地調用都需要在服務器端記log，這樣就只需要在StdMessageReceiver添加打log的功能，而不會影響RMIMessageReceiver。

MessageReceiverFactory簡單工廠用于生產MessageReceiver對象，可能是客戶端的RemoteMessageReceiver也可能是服務器端的StdMessageReceiver。

為了在deploy時候就啟動RMI服務，我們可以在servlet的init方法中初始化并注冊RMI服務，在deetroy方法中相應的取消RMI服務。

RemotableMessageReceiver: 遠程服務對象接口

public interface RemotableMessageReceiver extends Remote {

void invokeProcessFlow(String processId) throws ServerReceiverException,

RemoteException;

}

RMIMessageReceiver：提供RMI服務的遠程對象

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存儲的是一些配置信息，比如是不是服務器端，是不是需要開啟遠程服務，如果開啟的話相應的host，port和rmi遠程對象綁定的服務名

StdMessageReceiver：服務器端使用的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);

}

MessageReceiverFactory: 生產MessageReceiver的簡單工廠：

public class MessageReceiverFactory {

private static MessageReceiver messageReceiver;

private static RemotableMessageReceiver remotableMessageReceiver;

private static void init() throws ServerReceiverException {

SystemInfo sysInfo = ContextFactory.getSystemConfigContext()

.getSystemInfo();

if (sysInfo.isServer()) {

MessageReceiver mifMessageReceiver = new ServerMessageReceiver();

if (sysInfo.isRemoteable()) {

try {

remotableMessageReceiver = new RMIMessageReceiver(mifMessageReceiver);

} catch (RemoteException e) {

throw new ServerReceiverException(

"bind Message Receiver to port: "

+ sysInfo.getRmiport()

+ " with service name: "

+ sysInfo.getReceiverRmiBindName(), e);

}

messageReceiver = new StdMessageReceiver(mifMessageReceiver);

} else {

String rmiHost = sysInfo.getRmiHost();

int rmiPort = sysInfo.getRmiport();

String serviceName = sysInfo.getReceiverRmiBindName();

messageReceiver = createRemoteMesageReceiver(rmiHost, rmiPort,

serviceName);

}

public static MessageReceiver createRemoteMesageReceiver(String rmiHost,

int rmiPort, String serviceName) throws ServerReceiverException {

return new RemoteMessageReceiver(rmiHost, rmiPort, serviceName);

}

public synchronized static MessageReceiver getMessageReceiver() throws ServerReceiverException {

if(messageReceiver == null) {

init();

}

return messageReceiver;

}

public static RemotableMessageReceiver getRemoteableMesageReceiver(){

return remotableMessageReceiver;

}

public synchronized static void initMessageReceiver() throws ServerReceiverException {

init();

}

StartUpServlet:啟動時（deploy）時parse config并且初始化MessageReceiver

publicclass StartupServlet extends HttpServlet {

      public void init(ServletConfig config) throws ServletException {

            try {

                  //parse configuration



                  //init rmi service

                  MessageReceiverFactory.initMessageReceiver();



            } catch (Exception ex) {

                  ex.printStackTrace();

                  thrownew ServletException(ex.getMessage(), ex);

            }

      }

      publicvoid destroy() {

            try {



                  RemotableMessageReceiver remotableMessageReceiver = MessageReceiverFactory

                              .getRemoteableMesageReceiver();

                  if (remotableMessageReceiver != null) {

                        SystemInfo sysInfo = ContextFactory.getSystemConfigContext()

                                    .getSystemInfo();

                        RMIUtils.unBind(sysInfo.getRmiport(), sysInfo

                                    .getReceiverRmiBindName(),

                                    remotableMessageReceiver);

                  }

            } catch (Exception e) {

                  e.printStackTrace();

            }

      }

}

RMIUtils: 工具類提供rmi注冊和撤銷服務的功能：

public class RMIUtils {

public static void bind(int rmiPort, String serviceName, Remote remoteObject)

throws RemoteException {

SystemInfo sysInfo = ContextFactory.getSystemConfigContext()

.getSystemInfo();

Remote exportable = (Remote) UnicastRemoteObject

.exportObject(remoteObject);

Registry registry = null;

try {

registry = LocateRegistry.getRegistry(sysInfo.getRmiport());

registry.list();

} catch (Exception e) {

registry = LocateRegistry.createRegistry(sysInfo.getRmiport());

}

registry.list();

System.out.println("bind the service: " + serviceName);

String bindName = serviceName;

registry.rebind(bindName, exportable);

}

public static void unBind(int rmiPort, String serviceName, Remote remoteObject) throws RemoteException {

SystemInfo sysInfo = ContextFactory.getSystemConfigContext()

.getSystemInfo();

Registry registry = LocateRegistry.getRegistry(sysInfo.getRmiport());

String bindName = serviceName;

try {

registry.unbind(bindName);

UnicastRemoteObject.unexportObject(remoteObject, true);

} catch (java.rmi.NotBoundException nbe) {

}

posted on 2008-10-26 18:46 叱咤紅人閱讀(1517) 評論(1) 編輯收藏所屬分類: Design and Analysis Pattern 、J2SE and JVM 、Other Java and J2EE frameworks


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