同步转异步+RPC的一个POS行业应用-关键技术实现

简单回顾下业务模型：收银台<=>POS代理服务器<=>POS机，三者之间进行通讯，POS代理作为一个报文转换和同步转异步角色。

下面介绍下几个关键技术实现:

1、报文

这里的报文，指的是POS代理服务器跟POS通讯之间约定的报文。根据POS交易类型，支付、刷卡、打印等，约定每个交易报文包含什么字段信息和长度，其中一个比较特别字段是UUID，这个字段是每个报文的关键字段，
具有唯一性，每个报文都不同，主要用来实现同步转异步中，POS返回数据给代理服务器后找回原来发送指令的channel，并最终把转换后的数据发送给收银台。

之所以要找到原来的channel，是因为同步转异步的过程中，channel是被临时保存起来的。

2、同步转异步关键代码

public class PosResponseFuture<I> {      private final Lock lock = new ReentrantLock();  private final Condition done = lock.newCondition();    private String uuid;//消息序列号    //psoresponse使用  private final static Map<String, PosResponseFuture> futures = new ConcurrentHashMap<String, PosResponseFuture>();  private final static Object synLock = new Object();    public I write2pos(boolean broadcastFlag,MsgRequest msg) throws PosConnException,TimeOutException,TryLaterException {      synchronized(synLock)  {  long st = System.currentTimeMillis();    lock.lock();  try {  this.uuid = msg.getId();  futures.put(this.uuid, this);//把当前调用环境保存起来    //向pos发送消息  log.debug("向POS发送消息：{}",msg);    PosIntContext.write2pos(msg);    int timeout = PosIntContext.getApiTimeout();  if (msg.getTimeout()!=-1)  {  timeout = msg.getTimeout();  log.debug("超时设置：{}",timeout);  }  //这里是同步转异步关键  //程序执行到这里，一直处于阻塞状态，直到POS返回  //这里还设置了一个超时时间，避免POS出现故障，导致调用一直在等待  done.await(timeout,TimeUnit.SECONDS);  if (!isDone())  {  throw new TimeOutException("超时("+timeout+"秒)");  }    } catch (InterruptedException e) {  log.error("write2pos InterruptedException: "+e.getMessage());  throw new PosConnException(e);  } catch (TimeOutException e) {  throw e;  } catch (PosConnException e) {  throw e;  } catch (TryLaterException e) {  throw e;  }  finally {  this.release();  lock.unlock();  }    long en = System.currentTimeMillis();    log.debug("{} 执行时间:{}",msg.toString(),(en-st));  //POS执行完成，正常返回  if (response instanceof MsgResponse)  {  return (I)response;  }    return null;  }    }    /** * pos返回消息回调 * @Title: received * @Description: TODO * @param @param response * @return void * @throws */  public static void received(MsgResponse response) {  //用主键取回调用环境  PosResponseFuture<?> future = futures.remove(response.getId());    if (future != null) {  future.doReceived(response);  }    }    /** * 检测返回值 * @Title: isDone * @Description: TODO * @param @return * @return boolean * @throws */  private boolean isDone() {  return this.response != null;//null代表超时  }    /** * 接受到返回 * @Title: doReceived * @Description: TODO * @param @param response * @return void * @throws */  private void doReceived(MsgResponse response) {  lock.lock();//同步控制，线程安全  try {  this.response = response;  done.signal();//notify，通知线程往下执行  } finally {  lock.unlock();  }  }    /** * 释放资源 * @Title: release * @Description: TODO * @param * @return void * @throws */  private void release()  {  PosResponseFuture<I> tmp = futures.remove(this.uuid);  if (tmp!=null)  {    log.debug("释放资源：{}",new Object[]{this.uuid,tmp.getProcessMsg()});  }  else  {  log.debug("释放资源：NULL!");  }  }    public static void main(String args[])  {  }    } 

3、POS代理服务器暴露RPC调用接口关键代码

public class Client {//这个代码包含了rpc调用的核心@SuppressWarnings("unchecked")public <T> T getProxy(Class<T> interfaceClass,final  String host,final  int port) {return (T) Proxy.newProxyInstance(interfaceClass.getClassLoader(),new Class<?>[] { interfaceClass }, new InvocationHandler() {//其实就是一个AOP拦截public Object invoke(Object proxy, Method method,Object[] arguments) throws Throwable {Socket socket = null;ObjectOutputStream output = null;ObjectInputStream input = null;try{//把需要调用的类、方法和参数，序列化传输到RPC服务器//等待远端调用完成返回结果socket = new Socket(host, port);output = new ObjectOutputStream(socket.getOutputStream());output.writeUTF(method.getName());output.writeObject(method.getParameterTypes());output.writeObject(arguments);input = new ObjectInputStream(socket.getInputStream());return input.readObject();}catch(Exception e){throw e;}finally{if (socket!=null){socket.close();}if (output!=null){output.close();}if (input!=null){input.close();}}}});}public static void main(String args[]){HelloService helloService = new Client().getProxy(HelloService.class,"localhost",8080);long st = System.currentTimeMillis();for (int i=0; i<1; i++){System.out.println(i+"> "+helloService.sayHello("哈哈"));}long en = System.currentTimeMillis();System.out.println("耗时："+(en-st));}}public class Server {private int port = 8888;public void rpcServer()throws Exception{ServerSocket server = null;try{server = new ServerSocket(port);for(;;) {final Socket socket = server.accept();System.out.println(socket.getRemoteSocketAddress());new Thread(new Runnable() {@Overridepublic void run() {ObjectOutputStream output = null;ObjectInputStream input = null;try{input = new ObjectInputStream(socket.getInputStream());//接受rpc client请求String methodName = input.readUTF();//调用方法名Class<?>[] parameterTypes = (Class<?>[])input.readObject();Object[] arguments = (Object[])input.readObject();//调用参数output = new ObjectOutputStream(socket.getOutputStream());Method method =  new HelloServiceImp().getClass().getMethod(methodName, parameterTypes);Object result = method.invoke(new HelloServiceImp(), arguments);//执行调用output.writeObject(result);//回写结果}catch(Exception e){e.printStackTrace();}finally{try{if (output!=null){output.close();}if (input!=null){input.close();}}catch(Exception e){}}}}).start();}}catch(Exception e){throw e;}finally{if (server!=null){server.close();}}}public static void main(String args[]) throws Exception{new Server().rpcServer();}}public interface HelloService {public String sayHello(String input);}public class HelloServiceImp implements HelloService {@Overridepublic String sayHello(String input) {return input + " wellcome.";}}