Active Objects设计模式

   Active是主动的意思，Active Object是主动对象的意思。主动对象就是拥有自己的独立线程。 Active Object模式不仅有自己的独立线程，还可以接受异步消息，并能返回处理结果。从标准的Active Objects设计入手，将一个接口的方法调用转换成可接收异步消息的主动对象，也就是说方法的执行和方法的调用是在不同的线程中进行的，接口方法的参数以及具体的实现封装成特定的Message告诉执行线程，接口方法需要返回值，必须以Future形式返回。

   第一种方法：当某个线程调用OrderService接口的findOrderDetails方法时，是会发送一个包含findOrderDetails方法参数以及OrderService具体实现的Message到Message队列，执行线程通过从队列中获取Message来调用具体的实现，接口的方法的调用和接口方法的执行分别处于不同的线程中，因此称该接口为Active Objects（可接受异步消息的主动对象）。 具体样例代码如下：

public interface OrderService {
Future findOrderDetails(long orderId);
void order(String account,long orderId);
}

public class OrderServiceImpl implements OrderService{
@Override
public Future findOrderDetails(long orderId) {
return FutureService.newService().submit(input->{
try {
System.out.println("process the orderId->"+orderId);
TimeUnit.SECONDS.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "The order details Information";
},orderId);
}

@Override
public void order(String account, long orderId) {
try {
System.out.println("process the orderId->"+orderId+" , account->"+account);
TimeUnit.SECONDS.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

public class OrderServiceProxy implements OrderService{
private final OrderService orderService;
private final ActiveMessageQueue activeMessageQueue;

public OrderServiceProxy(OrderService orderService,ActiveMessageQueue activeMessageQueue) {
this.orderService=orderService;
this.activeMessageQueue=activeMessageQueue;
}

@Override
public Future findOrderDetails(long orderId) {
final ActiveFuture activeFuture=new ActiveFuture<>();
Map params=new HashMap<>();
params.put("orderId", orderId);
params.put("activeFuture", activeFuture);
MethodMessage message=new FindOrderDetailsMessage(params,orderService);
activeMessageQueue.offer(message);
return activeFuture;
}

@Override
public void order(String account, long orderId) {
Map params=new HashMap<>();
params.put("account", account);
params.put("orderId", orderId);
MethodMessage message=new OrderMessage(params,orderService);
System.out.println("processing in OrderServicePoxy.order method");
activeMessageQueue.offer(message);
}

}

public class ActiveFuture extends FutureTask{
@Override
public void finish(T result) {
super.finish(result);
}
}

import java.util.Map;

public abstract class MethodMessage {
protected final Map params;
protected final OrderService orderService;

public MethodMessage(Map params,OrderService orderService) {
this.params=params;
this.orderService=orderService;
}

public abstract void execute();
}

public class FindOrderDetailsMessage extends MethodMessage{

public FindOrderDetailsMessage(Map params, OrderService orderService) {
super(params, orderService);
}

@Override
public void execute() {
Future realFuture=orderService.findOrderDetails((Long) params.get("orderId"));
ActiveFuture activeFuture=(ActiveFuture)params.get("activeFuture");
try {
String result=realFuture.get();
activeFuture.finish(result);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

import java.util.Map;

public class OrderMessage extends MethodMessage{

public OrderMessage(Map params, OrderService orderService) {
super(params, orderService);
}

@Override
public void execute() {
String account=(String)params.get("account");
long orderId=(long)params.get("orderId");
orderService.order(account, orderId);
}

}

import java.util.LinkedList;

public class ActiveMessageQueue {
private final LinkedList message=new LinkedList<>();

public ActiveMessageQueue() {
System.out.println("active Object Thread is build");
new ActiveDaemonThread(this).start();
}

public void offer(MethodMessage methodMessage) {
synchronized(this) {
message.add(methodMessage);
System.out.println("processing in ActiveMessageQueue.offer method");
this.notify();
}
}

protected MethodMessage take() {
synchronized(this) {
while(message.isEmpty()) {
try {
this.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
System.out.println("processing in ActiveMessageQueue.take method");
return message.removeFirst();
}
}
}

public class ActiveDaemonThread extends Thread{
private final ActiveMessageQueue queue;

public ActiveDaemonThread(ActiveMessageQueue queue) {
super("ActiveDaemonThread");
this.queue=queue;
this.setDaemon(true);
}

@Override
public void run() {
for(;;) {
System.out.println(" active daemon thread is running");
MethodMessage methodMessage=this.queue.take();
methodMessage.execute();
}
}

}

public class OrderServiceFactory {
private final static ActiveMessageQueue activeMessageQueue=new ActiveMessageQueue();

private OrderServiceFactory() {}

public static OrderService toActiveObject(OrderService orderService) {
return new OrderServiceProxy(orderService,activeMessageQueue);
}

}

public class AOtest {

public static void main(String[] args) {
OrderService orderService=OrderServiceFactory.toActiveObject(new OrderServiceImpl());
orderService.order("aACC", 5);
Future f=orderService.findOrderDetails(50);
try {
System.out.println("future result is "+f.get());
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("Return immedately");
try {
Thread.currentThread().join();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

    第二种方法：第一种方法在接口方法非常多的情况下，会需要封装成很多的Message类。基于JDK动态代理的方式，可以实现一种更加通用的Active Objects。这种方式下，可以将任意接口方法转换w Active Objects，如果接口方法有返回值，必须返回Future类型才可以，否则会抛出IllegalActiveMethod异常。示例代码如下：

public class IllegalActivedException extends Exception{
public IllegalActivedException(String message) {
super(message);
}
}

public interface OrderService {
Future findOrderDetails(long orderId);
void order(String account,long orderId);
}

public class OrderServiceImpl implements OrderService{

@ActiveMethod
@Override
public Future findOrderDetails(long orderId) {
return FutureService.newService().submit(input->{
try {
System.out.println("process the orderId->"+orderId);
TimeUnit.SECONDS.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return "The order details Information";
},orderId);
}

@ActiveMethod
@Override
public void order(String account, long orderId) {
try {
System.out.println("process the orderId->"+orderId+" , account->"+account);
TimeUnit.SECONDS.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

@Retention(RUNTIME)
@Target(METHOD)
public @interface ActiveMethod {

}

public class ActiveMessage {
private final Object[] objects;
private final Method method;
private final ActiveFuture