扒一扒RPC
rpc原理
rpc
发布日期:   2021-04-05
作者:   欧阳思海
文章字数:   2.8k
阅读时长:   14 分
阅读次数:  
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原文链接：blog.ouyangsihai.cn >> 扒一扒RPC

前言：

本篇文章是继JDK动态代理超详细源码分析之后的，因为RPC是基于动态代理的。想必大家都听过RPC，但是可能并没有针对的去了解过，因此本文打算以如下结构讲一讲RPC：

①尽量浅显易懂的描述RPC的工作原理。

②分析一个RPC的Demo。

一、 走近RPC

1.1 什么是RPC

RPC是Remote Procedure Call的缩写，即远程过程调用，意思是可以在一台机器上调用远程的服务。在非分布式环境下，我们的程序调用服务都是本地调用，但是随着分布式结构的普遍，越来越多的应用需要解耦，将不同的独立功能部署发布成不同的服务供客户端调用。RPC就是为了解决这个问题的。

1.2 RPC原理

首先，我们心里带着这样的问题：要怎么样去调用远程的服务呢？

①肯定要知道IP和端口吧（确定唯一一个进程）

②肯定要知道调用什么服务吧（方法名和参数）

③调用服务后可能需要结果吧。

这三点又怎么实现呢？往下看：

RPC的设计由Client，Client stub，Network ，Server stub，Server构成。

其中Client就是用来调用服务的，Cient stub是用来把调用的方法和参数序列化的（因为要在网络中传输，必须要把对象转变成字节），Network用来传输这些信息到Server stub， Server stub用来把这些信息反序列化的，Server就是服务的提供者，最终调用的就是Server提供的方法。

RPC的结构如下图：

 

图中1-10序号的含义如下：

  1. Client像调用本地服务似的调用远程服务；
  2. Client stub接收到调用后，将方法、参数序列化
  3. 客户端通过sockets将消息发送到服务端
  4. Server stub 收到消息后进行解码（将消息对象反序列化）
  5. Server stub 根据解码结果调用本地的服务
  6. 本地服务执行(对于服务端来说是本地执行)并将结果返回给Server stub
  7. Server stub将返回结果打包成消息（将结果消息对象序列化）
  8. 服务端通过sockets将消息发送到客户端
  9. Client stub接收到结果消息，并进行解码（将结果消息发序列化）
  10. 客户端得到最终结果。

二、简单RPC程序

在了解了RPC的大致原理之后，我们给出RPC的示例。这里直接引用梁飞大神的代码，后面给出代码分析：

2.1 核心框架类

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/* * 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  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 ClassT 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();                }            }        });    }}

/*

  • 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 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 refer(final Class 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();
}
}
});
}
}

2.2 定义服务接口

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/* * 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);}

/*

  • 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);
}

2.3 实现服务

123456789101112131415161718
/* * 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;    }}

/*

  • 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;
}
}

2.4 暴露服务

1234567891011121314151617181920
/* * 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);    }}

/*

  • 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);
}
}

2.5 引用服务

123456789101112131415161718192021222324
/* * 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);        }    }}

/*

  • 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);
}
}
}

代码写的简单清晰又很能说明问题，不得不佩服大佬的技术。回过头来，我们分析一下这个程序的结构。

再次把RPC的5个组成部分回顾一下：Cient, Client-stub, Network, Server,Server-stub。

首先2.2定义服务接口和2.3实现服务都是在Server端实现的。写完了服务之后需要发布出去，以供客户端调用。于是在2.4暴露服务中调用 export方法把服务发布出去。export有一个参数是服务实现的对象service，这就给客户端提供了调用的可能性。我们看看export里都做了什么：

ServerSocket server = new ServerSocket(port); 创建ServerSocket并绑定接口。 然后是个无限循环，因为一直提供服务嘛， final Socket socket = server.accept(); 以阻塞的方式监听网络连接。开一个线程去处理客户端发过来的信息（反序列化方法名，参数类型，参数对象），这部分功能相当于Server-stub。然后通过反射机制调用服务对象的方法，并把得到的结果序列化返回给客户端。

看客户端，也就是2.5引用服务。通过refer函数得到服务的对象（这个对象就是通过动态代理生成的代理对象）。然后像调用本地方法一样调用远程方法。我们看下refer里都做了什么：

12
return (T) Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class?[] {interfaceClass}, new InvocationHandler()
{...重写invoke方法})

return (T) Proxy.newProxyInstance(interfaceClass.getClassLoader(), new Class?[] {interfaceClass}, new InvocationHandler()
{…重写invoke方法})

主要是返回服务实现类的代理对象，我们在分析JDK动态代理的时候知道，当我们调用代理对象的方法时，invoke方法会被执行。在invoke方法中， Socket socket = new Socket(host, port); 创建Socket与服务器取得连接。然后将方法名，方法类型，方法参数序列化发给服务器端，这部分功能相当于Client-stub。然后获得服务器端发送过来的结果。

这样RPC的功能就实现了。

本人花费半年的时间总结的《Java面试指南》已拿腾讯等大厂offer，已开源在github ，欢迎star！

本文GitHub https://github.com/OUYANGSIHAI/JavaInterview 已收录，这是我花了6个月总结的一线大厂Java面试总结，本人已拿大厂offer，欢迎star

原文链接：blog.ouyangsihai.cn >> 扒一扒RPC

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