简单了解RPC实现原理

时下很多企业应用更新换代到分布式，一篇文章了解什么是RPC。

原作者梁飞，在此记录下他非常简洁的rpc实现思路。

/*
* Copyright 2011 Alibaba.com All right reserved. This software is the
* confidential and proprietary information of Alibaba.com ("Confidential
* Information"). You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement you entered
* into with Alibaba.com.
*/
package com.alibaba.study.rpc.framework;

import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.net.ServerSocket;
import java.net.Socket;

/**
* RpcFramework
*
* @author william.liangf
*/
public class RpcFramework {

/**
* 暴露服务
*
* @param service 服务实现
* @param port 服务端口
* @throws Exception
*/
public static void export(final Object service, int port) throws Exception {
if (service == null)
throw new IllegalArgumentException("service instance == null");
if (port <= 0 || port > 65535)
throw new IllegalArgumentException("Invalid port " + port);
System.out.println("Export service " + service.getClass().getName() + " on port " + port);
ServerSocket server = new ServerSocket(port);
for(;;) {
try {
final Socket socket = server.accept();
new Thread(new Runnable() {
@Override
public void run() {
try {
try {
ObjectInputStream input = new ObjectInputStream(socket.getInputStream());
try {
String methodName = input.readUTF();
Class<?>[] parameterTypes = (Class<?>[])input.readObject();
Object[] arguments = (Object[])input.readObject();
ObjectOutputStream output = new ObjectOutputStream(socket.getOutputStream());
try {
Method method = service.getClass().getMethod(methodName, parameterTypes);
Object result = method.invoke(service, arguments);
output.writeObject(result);
} catch (Throwable t) {
output.writeObject(t);
} finally {
output.close();
}
} finally {
input.close();
}
} finally {
socket.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
} catch (Exception e) {
e.printStackTrace();
}
}
}

/**
* 引用服务
*
* @param <T> 接口泛型
* @param interfaceClass 接口类型
* @param host 服务器主机名
* @param port 服务器端口
* @return 远程服务
* @throws Exception
*/
@SuppressWarnings("unchecked")
public static <T> T refer(final Class<T> interfaceClass, final String host, final int port) throws Exception {
if (interfaceClass == null)
throw new IllegalArgumentException("Interface class == null");
if (! interfaceClass.isInterface())
throw new IllegalArgumentException("The " + interfaceClass.getName() + " must be interface class!");
if (host == null || host.length() == 0)
throw new IllegalArgumentException("Host == null!");
if (port <= 0 || port > 65535)
throw new IllegalArgumentException("Invalid port " + port);
System.out.println("Get remote service " + interfaceClass.getName() + " from server " + host + ":" + port);
return (T) Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class<?>[] {interfaceClass}, new InvocationHandler() {
public Object invoke(Object proxy, Method method, Object[] arguments) throws Throwable {
Socket socket = new Socket(host, port);
try {
ObjectOutputStream output = new ObjectOutputStream(socket.getOutputStream());
try {
output.writeUTF(method.getName());
output.writeObject(method.getParameterTypes());
output.writeObject(arguments);
ObjectInputStream input = new ObjectInputStream(socket.getInputStream());
try {
Object result = input.readObject();
if (result instanceof Throwable) {
throw (Throwable) result;
}
return result;
} finally {
input.close();
}
} finally {
output.close();
}
} finally {
socket.close();
}
}
});
}

}

定义服务接口

/*
* Copyright 2011 Alibaba.com All right reserved. This software is the
* confidential and proprietary information of Alibaba.com ("Confidential
* Information"). You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement you entered
* into with Alibaba.com.
*/
package com.alibaba.study.rpc.test;

/**
* HelloService
*
* @author william.liangf
*/
public interface HelloService {

String hello(String name);

}

实现服务

/*
* Copyright 2011 Alibaba.com All right reserved. This software is the
* confidential and proprietary information of Alibaba.com ("Confidential
* Information"). You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement you entered
* into with Alibaba.com.
*/
package com.alibaba.study.rpc.test;

/**
* HelloServiceImpl
*
* @author william.liangf
*/
public class HelloServiceImpl implements HelloService {

public String hello(String name) {
return "Hello " + name;
}

}

暴露服务

/*
* Copyright 2011 Alibaba.com All right reserved. This software is the
* confidential and proprietary information of Alibaba.com ("Confidential
* Information"). You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement you entered
* into with Alibaba.com.
*/
package com.alibaba.study.rpc.test;

import com.alibaba.study.rpc.framework.RpcFramework;

/**
* RpcProvider
*
* @author william.liangf
*/
public class RpcProvider {

public static void main(String[] args) throws Exception {
HelloService service = new HelloServiceImpl();
RpcFramework.export(service, 1234);
}

}

引用服务

/*
* Copyright 2011 Alibaba.com All right reserved. This software is the
* confidential and proprietary information of Alibaba.com ("Confidential
* Information"). You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement you entered
* into with Alibaba.com.
*/
package com.alibaba.study.rpc.test;

import com.alibaba.study.rpc.framework.RpcFramework;

/**
* RpcConsumer
*
* @author william.liangf
*/
public class RpcConsumer {

public static void main(String[] args) throws Exception {
HelloService service = RpcFramework.refer(HelloService.class, "127.0.0.1", 1234);
for (int i = 0; i < Integer.MAX_VALUE; i ++) {
String hello = service.hello("World" + i);
System.out.println(hello);
Thread.sleep(1000);
}
}

}

这个简单的例子的实现思路是使用阻塞的socket IO流来进行server和client的通信，也就是rpc应用中服务提供方和服务消费方。并且是端对端的，用端口号来直接进行通信。方法的远程调用使用的是jdk的动态代理，参数的序列化也是使用的最简单的objectStream。

真实的rpc框架会对上面的实现方式进行替换，采用更快更稳定，更高可用易扩展，更适宜分布式场景的中间件，技术来替换。例如使用netty的nio特性达到非阻塞的通信，使用zookeeper统一管理服务注册与发现，解决了端对端不灵活的劣势。代理方式有cglib字节码技术。序列化方式有hession2，fastjson等等。不过梁飞大大的博客使用原生的jdk api就展现给各位读者一个生动形象的rpc demo，实在是强。rpc框架解决的不仅仅是技术层面的实现，还考虑到了rpc调用中的诸多问题，重试机制，超时配置…这些就需要去了解成熟的rpc框架是如果考虑这些问题的了。

推荐一个轻量级的rpc框架：motan。weibo团队在github开源的一个rpc框架，有相应的文档，用起来感觉比dubbo要轻量级，易上手。