簡單RPC實現之Netty實現

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所謂RPC就是遠程方法調用(Remote  Process Call ),簡單的來說就是通過MQ,TCP,HTTP或者自己寫的網路通訊協定來傳輸我要調用對方的什麼介面,對方處理之後再把結果返回給我.就這麼簡單的一個過程。

運行時,一次客戶機對伺服器的RPC調用,其內部操作大致有如下十步：
1、調用用戶端控制代碼；執行傳送參數
2、調用本地系統核心發送網路訊息
3、訊息傳送到遠程主機
4、伺服器控制代碼得到訊息並取得參數
5、執行遠程過程
6、執行的過程將結果返回伺服器控制代碼
7、伺服器控制代碼返回結果，調用遠程系統核心
8、訊息傳回本地主機
9、客戶控制代碼由核心接收訊息
10、客戶接收控制代碼返回的資料

之前一篇文章簡單RPC之Socket實現我們通過socket通訊實現了簡單的RPC調用，接下來我們基於Netty來實現一個簡單的RPC調用過程，當然還有很多不完善的地方，只供參考學習RPC使用。

一、首先定義訊息傳遞的實體類

public class ClassInfo implements Serializable {private static final long serialVersionUID = -8970942815543515064L;private String className;//類名private String methodName;//函數名稱private Class<?>[] types;//參數類型  private Object[] objects;//參數列表  public String getClassName() {return className;}public void setClassName(String className) {this.className = className;}public String getMethodName() {return methodName;}public void setMethodName(String methodName) {this.methodName = methodName;}public Class<?>[] getTypes() {return types;}public void setTypes(Class<?>[] types) {this.types = types;}public Object[] getObjects() {return objects;}public void setObjects(Object[] objects) {this.objects = objects;}}

二、建立Netty操作的服務端，以及具體操作

（1）服務端

public class RPCServer {private int port;public RPCServer(int port){this.port = port;}public void start(){EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap().group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).localAddress(port).childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {                    ChannelPipeline pipeline = ch.pipeline();                       pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));                          pipeline.addLast(new LengthFieldPrepender(4));                          pipeline.addLast("encoder", new ObjectEncoder());                            pipeline.addLast("decoder", new ObjectDecoder(Integer.MAX_VALUE, ClassResolvers.cacheDisabled(null)));                          pipeline.addLast(new InvokerHandler()); }}).option(ChannelOption.SO_BACKLOG, 128)                     .childOption(ChannelOption.SO_KEEPALIVE, true);ChannelFuture future = serverBootstrap.bind(port).sync();            System.out.println("Server start listen at " + port );          future.channel().closeFuture().sync();  } catch (Exception e) { bossGroup.shutdownGracefully();           workerGroup.shutdownGracefully();}}public static void main(String[] args) throws Exception {          int port;          if (args.length > 0) {              port = Integer.parseInt(args[0]);          } else {              port = 8080;          }          new RPCServer(port).start();      }  }

（2）服務端操作，由服務端我們看到具體的資料轉送操作是進行序列化的，具體的操作還是比較簡單的，就是擷取發送過來的資訊，這樣就可以通過反射獲得類名，根據函數名和參數值，執行具體的操作，將執行結果發送給用戶端。

public class InvokerHandler extends ChannelInboundHandlerAdapter {public static ConcurrentHashMap<String, Object> classMap = new ConcurrentHashMap<String,Object>();@Override      public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {          ClassInfo classInfo = (ClassInfo)msg;        Object claszz = null;if(!classMap.containsKey(classInfo.getClassName())){try {claszz = Class.forName(classInfo.getClassName()).newInstance();classMap.put(classInfo.getClassName(), claszz);} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {e.printStackTrace();}}else {claszz = classMap.get(classInfo.getClassName());}Method method = claszz.getClass().getMethod(classInfo.getMethodName(), classInfo.getTypes());          Object result = method.invoke(claszz, classInfo.getObjects());         ctx.write(result);        ctx.flush();          ctx.close();    }  @Override  public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {       cause.printStackTrace();       ctx.close();  }  }

三、用戶端，通過代理機制來觸發遠程調用

（1）用戶端，當執行具體的函數時會調用遠程操作，將具體操作的類、函數及參數資訊發送到服務端

public class RPCProxy {@SuppressWarnings("unchecked")public static <T> T create(Object target){ return (T) Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(), new InvocationHandler(){@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {ClassInfo classInfo = new ClassInfo();classInfo.setClassName(target.getClass().getName());classInfo.setMethodName(method.getName());classInfo.setObjects(args);classInfo.setTypes(method.getParameterTypes());ResultHandler resultHandler = new ResultHandler();        EventLoopGroup group = new NioEventLoopGroup();          try {              Bootstrap b = new Bootstrap();              b.group(group)               .channel(NioSocketChannel.class)               .option(ChannelOption.TCP_NODELAY, true)               .handler(new ChannelInitializer<SocketChannel>() {                   @Override                   public void initChannel(SocketChannel ch) throws Exception {                   ChannelPipeline pipeline = ch.pipeline();                               pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));                               pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));                               pipeline.addLast("encoder", new ObjectEncoder());                                 pipeline.addLast("decoder", new ObjectDecoder(Integer.MAX_VALUE, ClassResolvers.cacheDisabled(null)));                               pipeline.addLast("handler",resultHandler);                 }               });                ChannelFuture future = b.connect("localhost", 8080).sync();              future.channel().writeAndFlush(classInfo).sync();            future.channel().closeFuture().sync();          } finally {              group.shutdownGracefully();          }        return resultHandler.getResponse();}});}}

（2）擷取遠程調用返回的結果值

public class ResultHandler extends ChannelInboundHandlerAdapter {private Object response;          public Object getResponse() {      return response;  }      @Override      public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {          response=msg;          System.out.println("client接收到伺服器返回的訊息:" + msg);      }            @Override      public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {          System.out.println("client exception is general");      }  }

四、介面、實作類別及Main操作

介面：

public interface HelloRpc {String hello(String name);}

實作類別：

public class HelloRpcImpl implements HelloRpc {@Overridepublic String hello(String name) {return "hello "+name;}}

Main操作：

public class Main {public static void main(String [] args){HelloRpc helloRpc = new HelloRpcImpl();helloRpc = RPCProxy.create(helloRpc);System.err.println(helloRpc.hello("rpc"));}}

完整代碼地址github

簡單RPC實現之Netty實現