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:
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public interface MessageReceiver {
void invokeProcessFlow(String processId) throws ServerReceiverException;
}
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ServerMessageReceiver:
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public class ServerMessageReceiver implements MessageReceiver {
ServerMessageReceiver() {
}
public void invokeProcessFlow(String processId) throws ServerReceiverException {
//receive message
}
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MessageReceiverFactory:
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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;
}
}
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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。
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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);
}
}
}
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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
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public interface RemotableMessageReceiver extends Remote {
void invokeProcessFlow(String processId) throws ServerReceiverException,
RemoteException;
}
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RMIMessageReceiver：提供RMI服务的远程对象
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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);
}
}
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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。
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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);
}
}
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