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首先我们要知道RPC框架是啥

1 RPC
1.1 RPC概念
RPC（Remote Procedure Call Protocol） 远程过程调用协议。
RPC是一种通过网络从远程计算机程序上请求服务。
RPC主要作用就是不同的服务间方法调用就像本地调用一样便捷。
1.2 常用RPC技术或框架
应用级的服务框架：阿里的 Dubbo/Dubbox、Google gRPC、Spring Boot/Spring Cloud。
远程通信协议：RMI、Socket、SOAP(HTTP XML)、REST(HTTP JSON)。
通信框架：MINA 和 Netty

1.3 初始化工程：

Consumer（消费者）、Producer（生产者）、Producer-common（生产者接口）、SLQF-rpc（RPC模块）

在生产者接口模块里面创建一个接口HelloService

package com.producercommon.Service;public interface HelloService {String sayhello(String name);
}

然后在生产者和消费者模块中都导入生产者接口和RPC模块。

<dependency><groupId>com</groupId><artifactId>SLQF-rpc</artifactId><version>0.0.1-SNAPSHOT</version>
</dependency><dependency><groupId>com</groupId><artifactId>Producer-common</artifactId><version>0.0.1-SNAPSHOT</version>
</dependency>

在生产者模块实现HelloService接口

package com.producer.Impl;import com.producercommon.Service.HelloService;public class HelloServiceImpl implements HelloService {@Overridepublic String sayhello(String name) {return "hello:" + name;}
}

编写RPC框架
在消费者模块中，不能通过创建HelloServiceImpl对象来调用Producer中的sayhello方法，那就只能通过网络请求的方式来调用，接收网络请求的方式有很多
如Jetty，Tomcat，Netty，或者直接用Socket，这里选择使用的是Tomcat
在RPC模块中导入Tomcat依赖以及IO工具包

<dependency><groupId>org.apache.tomcat.embed</groupId><artifactId>tomcat-embed-core</artifactId><version>9.0.79</version>
</dependency><dependency><groupId>commons-io</groupId><artifactId>commons-io</artifactId><version>1.3.1</version>
</dependency>

需要在Producer服务启动时，启动Tomcat，在RPC模块中编写一个Tomcat启动方法，方法中的参数为IP地址和绑定的端口号

package com.youyuan;import org.apache.catalina.*;
import org.apache.catalina.connector.Connector;
import org.apache.catalina.core.StandardContext;
import org.apache.catalina.core.StandardEngine;
import org.apache.catalina.core.StandardHost;
import org.apache.catalina.startup.Tomcat;public class HttpServer {public void start(String hostName, int port) {Tomcat tomcat = new Tomcat();Server server = tomcat.getServer();Service service = server.findService("Tomcat");Connector connector = new Connector();connector.setPort(port);Engine engine = new StandardEngine();engine.setDefaultHost(hostName);Host host = new StandardHost();host.setName(hostName);String contextPath = "";Context context = new StandardContext();context.setPath(contextPath);context.addLifecycleListener(new Tomcat.FixContextListener());host.addChild(context);engine.addChild(host);service.setContainer(engine);service.addConnector(connector);// 将所有请求都交给dispatcher处理tomcat.addServlet(contextPath, "dispatcher", new DispatcherServlet());context.addServletMappingDecoded("/*", "dispatcher");try {tomcat.start();tomcat.getServer().await();} catch (LifecycleException e) {e.printStackTrace();}}
}

其中使用的dispatcher为自定义的DispatcherServlet，用来处理收到的网络消息
同样在RPC模块中编写DispatcherServlet类

package com.youyuan;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;public class DispatcherServlet extends HttpServlet {@Overrideprotected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 抽象为Hander类new HttpServerHandler().handler(req, resp);}
}

将处理方式抽象为一个类，提升框架可扩展性，如果还要处理其他类型的网络消息，可以增加另外的Handler类，随后编写客户端发送的Invocation消息类

package com.youyuan;import java.io.Serializable;public class Invocation implements Serializable {// 接口名称private String interfaceName;// 需要调用的方法名private String methodName;// 方法中参数类型private Class[] types;// 方法的参数private Object[] args;public String getInterfaceName() {return interfaceName;}public void setInterfaceName(String interfaceName) {this.interfaceName = interfaceName;}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[] getArgs() {return args;}public void setArgs(Object[] args) {this.args = args;}public Invocation(String interfaceName, String methodName, Class[] types, Object[] args) {this.interfaceName = interfaceName;this.methodName = methodName;this.types = types;this.args = args;}
}

之后是发送网络消息的客户端方法，参数为IP地址，Tomcat服务器端口号，消息Invocation

package com.youyuan;import org.apache.commons.io.IOUtils;import java.io.InputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;public class HttpClient {public String send(String host, int port, Invocation invocation) {String result = null;try {URL url = new URL("http", host, port, "/");HttpURLConnection httpConnection = (HttpURLConnection) url.openConnection();httpConnection.setRequestMethod("POST");httpConnection.setDoOutput(true);OutputStream out = httpConnection.getOutputStream();ObjectOutputStream outStream = new ObjectOutputStream(out);outStream.writeObject(invocation);outStream.flush();outStream.close();InputStream inputStream = httpConnection.getInputStream();result =  IOUtils.toString(inputStream);return result;} catch (Exception e) {e.printStackTrace();}return result;}
}

当收到客户端发送网络消息后，Tomcat默认调用我们配置的DispatcherServlet，编写其中处理消息的Handler类

package com.youyuan;import org.apache.commons.io.IOUtils;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.ObjectInputStream;
import java.lang.reflect.Method;public class HttpServerHandler {public void handler(HttpServletRequest request, HttpServletResponse response){try {// 获取客户端传过来的Invocation消息Invocation invocation = (Invocation) new ObjectInputStream(request.getInputStream()).readObject();String interfaceName = invocation.getInterfaceName();String methodName = invocation.getMethodName();// 根据接口名称，获取想要调用的实现类Class clazz = LocalRegister.get(interfaceName);Method method = clazz.getMethod(methodName, invocation.getTypes());// 利用反射执行消费者想要调用的方法String result = (String)method.invoke(clazz.newInstance(), invocation.getArgs());// 返回方法的执行结果IOUtils.write(result, response.getOutputStream());} catch (Exception e) {e.printStackTrace();}}
}

这就是处理消息的类，也是调用服务关键所在，以下代码段中的LocalRegister类，是一个本地注册类，里面保存了接口与对应实现类的映射，保证调用的是想要的实现类的方法，以下是LocalRegister的代码

package com.youyuan;import java.util.*;public class LocalRegister {private static Map<String, Class> map = new HashMap<>();public static void register(String interfaceName, Class implClass) {map.put(interfaceName, implClass);}public static Class get(String ingerfaceName) {return map.get(ingerfaceName);}
}

RPC框架通常返回的是一个代理对象，然后来执行代理对象的方法来实现服务的调用，接下来我们来编写一下代理类

package com.youyuan;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;public class ProxyFactory {public static <T>T getProxy(Class interfaceClass) {Object proxy = Proxy.newProxyInstance(ProxyFactory.class.getClassLoader(), new Class[]{interfaceClass}, new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {// 使用反射来创建消息对象Invocation invocation = new Invocation(interfaceClass.getName(), method.getName(),method.getParameterTypes(), args);HttpClient client = new HttpClient();String result = client.send("localhost", 8080, invocation);return result;}});return (T)proxy;}
}

现在RPC框架的主要架构已经编写完成，可以进行测试一下，在Producer服务模块中启动Tomcat并且注册服务

package com.producer.Impl;import com.producercommon.Service.HelloService;
import com.youyuan.HttpServer;
import com.youyuan.LocalRegister;public class Producer {public static void main(String[] args) {// 注册服务LocalRegister.register(HelloService.class.getName(), HelloServiceImpl.class);HttpServer server = new HttpServer();server.start("localhost",8080);}
}

Consumer模块创建HelloService的代理对象来调用Producer中的服务了

package com.consumer;import com.producercommon.Service.HelloService;
import com.youyuan.ProxyFactory;public class Consumer {public static void main(String[] args) {HelloService helloService = ProxyFactory.getProxy(HelloService.class);String result = helloService.sayhello("小白鼬猿");System.out.println(result);}
}

执行代码，发现调用成功啦~：