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docs(from-readers): add an article about micro service
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- [微服务的事件驱动数据管理](/docs/micro-services/event-driven-data-management-for-microservices.md)
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### Spring Cloud 微服务架构
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- 什么是微服务？微服务之间是如何独立通讯的？
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- [什么是微服务？微服务之间是如何独立通讯的？](/docs/micro-services/huifer-what's-microservice-how-to-communicate.md)
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- Spring Cloud 和 Dubbo 有哪些区别？
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- Spring Boot 和 Spring Cloud，谈谈你对它们的理解？
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- 什么是服务熔断？什么是服务降级？
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# 什么是微服务？微服务之间是如何独立通讯的？
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- Author: [HuiFer](https://github.com/huifer)
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- Description: 介绍微服务的定义,服务之间的通讯,对RPC 和
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## 什么是微服务
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> 微服务架构是一个分布式系统, 按照业务进行划分成为不同的服务单元, 解决单体系统性能等不足.
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> 微服务是一种架构风格, 一个大型软件应用由多个服务单元组成. 系统中的服务单元可以单独部署, 各个服务单元之间是松耦合的.
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> 微服务概念起源: [Microservices](https://martinfowler.com/articles/microservices.html)
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>
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## 微服务之间是如何独立通讯的
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### 同步
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#### REST HTTP 协议
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> REST 请求在微服务中是最为常用的一种通讯方式, 它依赖于 HTTP\HTTPS 协议.
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- RESTFUL特点
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1. 每一个URI代表1种资源
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2. 客户端使用 GET、POST、PUT、DELETE 4个表示操作方式的动词对服务端资源进行操作: GET 用来获取资源, POST 用来新建资源(也可以用于更新资源), PUT 用来更新资源, DELETE 用来删除资源
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3. 通过操作资源的表现形式来操作资源
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4. 资源的表现形式是 XML 或者 HTML
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5. 客户端与服务端之间的交互在请求之间是无状态的,从客户端到服务端的每个请求都必须包含理解请求所必需的信息
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##### 例子
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- 有一个服务方提供了如下接口.
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```java
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@RestController
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@RequestMapping("/communication")
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public class RestControllerDemo {
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@GetMapping("/hello")
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public String s() {
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return "hello";
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}
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}
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```
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- 另外一个服务需要去调用该接口, 调用方只需要根据 API 文档发送请求即可获取返回结果.
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```java
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@RestController
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@RequestMapping("/demo")
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public class RestDemo{
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@Autowired
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RestTemplate restTemplate;
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@GetMapping("/hello2")
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public String s2() {
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String forObject = restTemplate.getForObject("http://localhost:9013/communication/hello", String.class);
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return forObject;
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}
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}
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```
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- 通过这样的方式可以实现服务之间的通讯
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#### RPC TCP协议
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> RPC(Remote Procedure Call)远程过程调用, 简单的理解是一个节点请求另一个节点提供的服务
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>
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>工作流程
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> 1. 执行客户端调用语句，传送参数
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> 2. 调用本地系统发送网络消息
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> 3. 消息传送到远程主机
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> 4. 服务器得到消息并取得参数
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> 5. 根据调用请求以及参数执行远程过程（服务）
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> 6. 执行过程完毕，将结果返回服务器句柄
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> 7. 服务器句柄返回结果，调用远程主机的系统网络服务发送结果
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> 8. 消息传回本地主机
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> 9. 客户端句柄由本地主机的网络服务接收消息
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> 10. 客户端接收到调用语句返回的结果数据
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- 这个不知道如何具体描述直接上代码.
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- 首先需要一个服务端
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```java
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import java.io.IOException;
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import java.io.ObjectInputStream;
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import java.io.ObjectOutputStream;
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import java.lang.reflect.Method;
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import java.net.InetSocketAddress;
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import java.net.ServerSocket;
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import java.net.Socket;
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import java.util.concurrent.ConcurrentHashMap;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.Executors;
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/**
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* RPC 服务端用来注册远程方法的接口和实现类
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* @Date: 2019-11-04
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*/
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public class RPCServer {
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private static ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
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private static final ConcurrentHashMap<String, Class> serviceRegister = new ConcurrentHashMap<>();
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/**
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* 注册方法
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* @param service
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* @param impl
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*/
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public void register(Class service, Class impl) {
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serviceRegister.put(service.getSimpleName(), impl);
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}
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/**
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* 启动方法
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* @param port
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*/
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public void start(int port) {
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ServerSocket socket = null;
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try {
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socket = new ServerSocket();
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socket.bind(new InetSocketAddress(port));
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System.out.println("服务启动");
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System.out.println(serviceRegister);
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while (true) {
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executor.execute(new Task(socket.accept()));
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}
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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if (socket != null) {
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try {
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socket.close();
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} catch (IOException e) {
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e.printStackTrace();
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}
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}
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}
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}
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private static class Task implements Runnable {
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Socket client = null;
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public Task(Socket client) {
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this.client = client;
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}
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@Override
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public void run() {
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ObjectInputStream input = null;
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ObjectOutputStream output = null;
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try {
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input = new ObjectInputStream(client.getInputStream());
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// 按照顺序读取对方写过来的内容
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String serviceName = input.readUTF();
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String methodName = input.readUTF();
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Class<?>[] parameterTypes = (Class<?>[]) input.readObject();
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Object[] arguments = (Object[]) input.readObject();
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Class serviceClass = serviceRegister.get(serviceName);
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if (serviceClass == null) {
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throw new ClassNotFoundException(serviceName + " 没有找到!");
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}
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Method method = serviceClass.getMethod(methodName, parameterTypes);
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Object result = method.invoke(serviceClass.newInstance(), arguments);
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output = new ObjectOutputStream(client.getOutputStream());
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output.writeObject(result);
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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try {
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// 这里就不写 output!=null才关闭这个逻辑了
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output.close();
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input.close();
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client.close();
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} catch (IOException e) {
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e.printStackTrace();
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}
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}
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}
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}
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}
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```
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- 其次需要一个客户端
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```java
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import java.io.ObjectInputStream;
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import java.io.ObjectOutputStream;
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import java.lang.reflect.InvocationHandler;
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import java.lang.reflect.Method;
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import java.lang.reflect.Proxy;
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import java.net.InetSocketAddress;
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import java.net.Socket;
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/**
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* RPC 客户端
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* @Date: 2019-11-04
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*/
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public class RPCclient<T> {
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/**
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* 通过动态代理将参数发送过去到 RPCServer ,RPCserver 返回结果这个方法处理成为正确的实体
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*/
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public static <T> T getRemoteProxyObj(final Class<T> service, final InetSocketAddress addr) {
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return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[]{service}, new InvocationHandler() {
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@Override
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public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
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Socket socket = null;
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ObjectOutputStream out = null;
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ObjectInputStream input = null;
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try {
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socket = new Socket();
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socket.connect(addr);
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// 将实体类,参数,发送给远程调用方
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out = new ObjectOutputStream(socket.getOutputStream());
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out.writeUTF(service.getSimpleName());
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out.writeUTF(method.getName());
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out.writeObject(method.getParameterTypes());
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out.writeObject(args);
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input = new ObjectInputStream(socket.getInputStream());
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return input.readObject();
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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out.close();
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input.close();
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socket.close();
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}
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return null;
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}
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});
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}
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}
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```
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- 再来一个测试的远程方法
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```java
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public interface Tinterface {
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String send(String msg);
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}
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public class TinterfaceImpl implements Tinterface {
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@Override
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public String send(String msg) {
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return "send message " + msg;
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}
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}
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```
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- 测试代码
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```java
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import com.huifer.admin.rpc.Tinterface;
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import com.huifer.admin.rpc.TinterfaceImpl;
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import java.net.InetSocketAddress;
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/**
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* @Date: 2019-11-04
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*/
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public class RunTest {
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public static void main(String[] args) {
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new Thread(new Runnable() {
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@Override
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public void run() {
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RPCServer rpcServer = new RPCServer();
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rpcServer.register(Tinterface.class, TinterfaceImpl.class);
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rpcServer.start(10000);
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}
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}).start();
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Tinterface tinterface = RPCclient.getRemoteProxyObj(Tinterface.class, new InetSocketAddress("localhost", 10000));
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System.out.println(tinterface.send("rpc 测试用例"));
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}
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}
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```
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- 输出`send message rpc 测试用例`
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### 异步
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#### 消息中间件
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> 常见的消息中间件有 Kafka、ActiveMQ、RabbitMQ、RocketMQ , 常见的协议有AMQP、MQTTP、STOMP、XMPP. 这里不对消息队列进行拓展了, 具体如何使用还是请移步官网.
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>
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