1.1 基于TCP协议的RPC
1.1.1 RPC名词解释
RPC的全称是Remote Process Call，即远程过程调用，RPC的实现包括客户端和服务端，即服务调用方和服务提供方。服务调用方发送RPC请求到服务提供方，服务提供方根据请求的参数执行请求方法，并将结果返回给服务调用方，一次RPC调用完成。
1.1.2 对象的序列化
在网络上传输的数据，无论何种类型，最终都需要转化为二进制流。在面向对象的程序设计中，客户端将对象转化为二进制流发送给服务端，服务端接收数据后将二进制流转化为对象，java中将这两种转化方式称为对象的序列化和反序列化。下面介绍java内置的序列化方式和基于java的Hessian序列化方式：
java内置的序列化和反序列化关键代码：
1 //序列化操作 2 Person person = new Person(); 3 ByteArrayOutputStream os = new ByteArrayOutputStream(); 4 ObjectOutputStream out = new ObjectOutputStream(os); 5 out.writeObject(person); 6 byte[] byteArray = os.toByteArray(); 7 8 //反序列化操作 9 ByteArrayInputStream is = new ByteArrayInputStream(byteArray); 10 ObjectInputStream in = new ObjectInputStream(is); 11 Person newPerson = new Person(); 12 newPerson = (Person) in.readObject();
基于java的Hessian序列化和反序列化关键代码：
1 //序列化操作 2 ByteArrayOutputStream osH = new ByteArrayOutputStream(); 3 HessianOutput outH = new HessianOutput(osH); 4 outH.writeObject(person); 5 byte[] byteArrayH = osH.toByteArray(); 6 7 //反序列化操作 8 ByteArrayInputStream isH = new ByteArrayInputStream(byteArrayH); 9 HessianInput inH = new HessianInput(isH); 10 newPerson = (Person) inH.readObject();
1.1.3 基于TCP协议实现RPC
我们利用java的SocketAPI实现一个简单的RPC调用，服务的接口和实现比较简单，根据传入的参数来判断返回"hello" or "bye bye"。
1 public interface SayHelloService { 2 3 public String sayHello(String arg); 4 } 5 6 public class SayHelloServiceImpl implements SayHelloService { 7 8 public String sayHello(String arg) { 9 return "hello".equals(arg) ? "hello" : "bye bye"; 10 } 11 12 }
服务消费者Consumer类：
1 /** 2 * 基于TCP协议实现RPC -- 服务消费者 3 * @author admin 4 * 5 */ 6 public class Consumer { 7 8 public static void main(String[] args) throws Exception { 9 //接口名称 10 String interfaceName = SayHelloService.class.getName(); 11 //需要执行远程的方法 12 Method method = SayHelloService.class.getMethod("sayHello", String.class); 13 //传递到远程的参数 14 Object [] arguments = {"hello"}; 15 Socket socket = new Socket("127.0.0.1", 1234); 16 //将方法名和参数传递到远端 17 ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream()); 18 out.writeUTF(interfaceName);//接口名称 19 out.writeUTF(method.getName());//方法名称 20 out.writeObject(method.getParameterTypes());//方法参数类型 21 out.writeObject(arguments);//传递的参数 22 System.out.println("发送信息到服务端，发送的信息为:" + arguments[0]); 23 //从远端读取返回结果 24 ObjectInputStream in = new ObjectInputStream(socket.getInputStream()); 25 String result = (String) in.readObject(); 26 System.out.println("服务返回的结果为：" + result); 27 } 28 }
服务提供者Provider类：
1 /** 2 * 基于TCP协议实现RPC -- 服务提供者 3 * @author admin 4 * 5 */ 6 public class Provider { 7 8 public static void main(String[] args) throws Exception { 9 ServerSocket server = new ServerSocket(1234); 10 Map<Object, Object> services = new HashMap<Object, Object>(); 11 services.put(SayHelloService.class.getName(), new SayHelloServiceImpl()); 12 while(true) { 13 System.out.println("服务提供者启动，等待客户端调用…………"); 14 Socket socket = server.accept(); 15 //读取服务信息 16 ObjectInputStream in = new ObjectInputStream(socket.getInputStream()); 17 String interfaceName = in.readUTF(); 18 String methodName = in.readUTF(); 19 Class<?>[] parameterTypes = (Class<?>[]) in.readObject(); 20 Object [] arguments = (Object[]) in.readObject(); 21 System.out.println("客户端调用服务端接口" + interfaceName + "的" + methodName + "方法"); 22 //执行调用 23 Class serviceClass = Class.forName(interfaceName);//得到接口的class 24 Object service = services.get(interfaceName);//取得服务实现的对象 25 Method method = serviceClass.getMethod(methodName, parameterTypes);//获得要调用的方法 26 Object result = method.invoke(service, arguments); 27 ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream()); 28 out.writeObject(result); 29 System.out.println("服务端返回结果为：" + result); 30 } 31 } 32 }
在真实的生产环境中往往是多个客户端同时请求服务端，服务端则需要同时接收和处理多个客户端请求消息，涉及并发处理、服务路由、负载均衡等现实问题，以上代码显然不能完成。
1.2 基于HTTP协议的RPC
1.2.1 HTTP协议栈
HTTP的全称是HyperText Transfer Protocol，即超文本传输协议，当今普遍采用的版本是HTTP1.1。HTTP协议属于应用层协议，它构建在TCP和IP协议之上，处于TCP/IP架构的顶端，为了更好的理解HTTP协议，我们基于java的SocketAPI设计一个简单的应用层通信协议，来窥探协议实现的一些过程与细节。
客户端向服务端发送一条命令，服务端接收到命令后，会判断命令是否为"HELLO"，若是则返回客户端"hello!",否则返回客户端"bye bye"。
1 /** 2 * 协议请求 3 * 4 * @author admin 5 * 6 */ 7 public class Request { 8 9 /** 10 * 协议编码 0：GBK；1：UTF-8 11 */ 12 private byte encode; 13 /** 14 * 命令 15 */ 16 private String command; 17 /** 18 * 命令长度 19 */ 20 private int commandLength; 21 22 public byte getEncode() { 23 return encode; 24 } 25 26 public void setEncode(byte encode) { 27 this.encode = encode; 28 } 29 30 public String getCommand() { 31 return command; 32 } 33 34 public void setCommand(String command) { 35 this.command = command; 36 } 37 38 public int getCommandLength() { 39 return commandLength; 40 } 41 42 public void setCommandLength(int commandLength) { 43 this.commandLength = commandLength; 44 } 45 46 }
1 /** 2 * 协议响应 3 * 4 * @author admin 5 * 6 */ 7 public class Response { 8 /** 9 * 编码 10 */ 11 private byte encode; 12 /** 13 * 响应 14 */ 15 private String response; 16 /** 17 * 响应长度 18 */ 19 private int responseLength; 20 21 public byte getEncode() { 22 return encode; 23 } 24 25 public void setEncode(byte encode) { 26 this.encode = encode; 27 } 28 29 public String getResponse() { 30 return response; 31 } 32 33 public void setResponse(String response) { 34 this.response = response; 35 } 36 37 public int getResponseLength() { 38 return responseLength; 39 } 40 41 public void setResponseLength(int responseLength) { 42 this.responseLength = responseLength; 43 } 44 45 @Override 46 public String toString() { 47 return "Response [encode=" + encode + ", response=" + response + ", responseLength=" + responseLength + "]"; 48 } 49 50 }
客户端发送以及服务端响应处理代码：
1 /** 2 * 服务端 3 * @author admin 4 * 5 */ 6 public class Server { 7 8 public static void main(String[] args) throws Exception { 9 ServerSocket server = new ServerSocket(1234); 10 while(true) { 11 Socket client = server.accept(); 12 //读取请求数据 13 Request request = ProtocolUtil.readRequest(client.getInputStream()); 14 //封装响应数据 15 Response response = new Response(); 16 response.setEncode(Encode.UTF8.getValue()); 17 response.setResponse(request.getCommand().equals("HELLO") ? "hello!" : "bye bye"); 18 response.setResponseLength(response.getResponse().length()); 19 //响应到客户端 20 ProtocolUtil.writeResponse(client.getOutputStream(), response); 21 } 22 } 23 } 24 25 /** 26 * 客户端 27 * @author admin 28 * 29 */ 30 public class Client { 31 32 public static void main(String[] args) throws Exception { 33 //组装请求数据 34 Request request = new Request(); 35 request.setCommand("HELLO"); 36 request.setCommandLength(request.getCommand().length()); 37 request.setEncode(Encode.UTF8.getValue()); 38 Socket client = new Socket("127.0.0.1", 1234); 39 //发送请求 40 ProtocolUtil.writeRequest(client.getOutputStream(), request); 41 //读取相应 42 Response response = ProtocolUtil.readResponse(client.getInputStream()); 43 System.out.println(response); 44 } 45 }
ProtocolUtil 类：
1 public class ProtocolUtil { 2 3 public static void writeRequest(OutputStream out, Request request) { 4 try { 5 out.write(request.getEncode()); 6 //write一个int值会截取其低8位传输，丢弃其高24位，因此需要将基本类型转化为字节流 7 //java采用Big Endian字节序，而所有的网络协议也都是以Big Endian字节序来进行传输，所以再进行数据的传输和接收时，需要先将数据转化成Big Endian字节序 8 //out.write(request.getCommandLength()); 9 out.write(int2ByteArray(request.getCommandLength())); 10 out.write(Encode.GBK.getValue() == request.getEncode() ? request.getCommand().getBytes("GBK") : request.getCommand().getBytes("UTF8")); 11 out.flush(); 12 } catch (Exception e) { 13 System.err.println(e.getMessage()); 14 } 15 } 16 17 /** 18 * 将响应输出到客户端 19 * @param os 20 * @param response 21 */ 22 public static void writeResponse(OutputStream out, Response response) { 23 try { 24 out.write(response.getEncode()); 25 out.write(int2ByteArray(response.getResponseLength())); 26 out.write(Encode.GBK.getValue() == response.getEncode() ? response.getResponse().getBytes("GBK") : response.getResponse().getBytes("UTF8")); 27 out.flush(); 28 } catch (Exception e) { 29 System.err.println(e.getMessage()); 30 } 31 } 32 33 public static Request readRequest(InputStream is) { 34 Request request = new Request(); 35 try { 36 //读取编码 37 byte [] encodeByte = new byte[1]; 38 is.read(encodeByte); 39 byte encode = encodeByte[0]; 40 //读取命令长度 41 byte [] commandLengthByte = new byte[4];//缓冲区 42 is.read(commandLengthByte); 43 int commandLength = byte2Int(commandLengthByte); 44 //读取命令 45 byte [] commandByte = new byte[commandLength]; 46 is.read(commandByte); 47 String command = Encode.GBK.getValue() == encode ? new String(commandByte, "GBK") : new String(commandByte, "UTF8"); 48 //组装请求返回 49 request.setEncode(encode); 50 request.setCommand(command); 51 request.setCommandLength(commandLength); 52 } catch (Exception e) { 53 System.err.println(e.getMessage()); 54 } 55 return request; 56 } 57 58 public static Response readResponse(InputStream is) { 59 Response response = new Response(); 60 try { 61 byte [] encodeByte = new byte[1]; 62 is.read(encodeByte); 63 byte encode = encodeByte[0]; 64 byte [] responseLengthByte = new byte[4]; 65 is.read(responseLengthByte); 66 int commandLength = byte2Int(responseLengthByte); 67 byte [] responseByte = new byte[commandLength]; 68 is.read(responseByte); 69 String resContent = Encode.GBK.getValue() == encode ? new String(responseByte, "GBK") : new String(responseByte, "UTF8"); 70 response.setEncode(encode); 71 response.setResponse(resContent); 72 response.setResponseLength(commandLength); 73 } catch (Exception e) { 74 System.err.println(e.getMessage()); 75 } 76 return response; 77 } 78 79 public static int byte2Int(byte [] bytes) { 80 int num = bytes[3] & 0xFF; 81 num |= ((bytes[2] << 8) & 0xFF00); 82 num |= ((bytes[1] << 16) & 0xFF0000); 83 num |= ((bytes[0] << 24) & 0xFF000000); 84 return num; 85 } 86 87 public static byte[] int2ByteArray(int i) { 88 byte [] result = new byte[4]; 89 result[0] = (byte) ((i >> 24) & 0xFF); 90 result[1] = (byte) ((i >> 16) & 0xFF); 91 result[2] = (byte) ((i >> 8) & 0xFF); 92 result[3] = (byte) (i & 0xFF); 93 return result; 94 } 95 96 }
1.2.2 HTTP请求与响应
下图是HTTP请求与响应的过程步骤，在此不详细赘述。
1.2.3 通过HttpClient发送HTTP请求
HttpClient对HTTP协议通信的过程进行了封装，下面是简单的通过HttpClient发送HTTP GET请求，并获取服务端响应的代码：
1 //url前加上http协议头，标明该请求为http请求 2 String url = "https://www.baidu.com"; 3 //组装请求 4 HttpClient httpClient = new DefaultHttpClient(); 5 HttpGet httpGet = new HttpGet(url); 6 //接收响应 7 HttpResponse response = httpClient.execute(httpGet); 8 HttpEntity entity = response.getEntity(); 9 byte[] byteArray = EntityUtils.toByteArray(entity); 10 String result = new String(byteArray, "utf8"); 11 System.out.println(result);
1.2.4 使用HTTP协议的优势
随着请求规模的扩展，基于TCP协议的RPC的实现，需要考虑多线程并发、锁、I/O等复杂的底层细节，在大流量高并发的压力下，任何一个小的错误都可能被无限放大，最终导致程序宕机。而对于基于HTTP协议的实现来说，很多成熟的开源web容易已经帮其处理好了这些事情，如Apache，Tomcat，Jboss等，开发人员可将更多的精力集中在业务实现上，而非处理底层细节。