今天,我们一起来实现一个轻量级的RPC框架。

RPC,即 Remote Procedure Call(远程过程调用),说得通俗一点就是:调用远程计算机上的服务,就像调用本地服务一样。

RPC 可基于 HTTP 或 TCP 协议,Web Service 就是基于 HTTP 协议的 RPC,它具有良好的跨平台性,但其性能却不如基于 TCP 协议的 RPC。会两方面会直接影响 RPC 的性能,一是传输方式,二是序列化。

众所周知,TCP 是传输层协议,HTTP 是应用层协议,而传输层较应用层更加底层,在数据传输方面,越底层越快,因此,在一般情况下,TCP 一定比 HTTP 快。就序列化而言,Java 提供了默认的序列化方式,但在高并发的情况下,这种方式将会带来一些性能上的瓶颈,于是市面上出现了一系列优秀的序列化框架,比如:Protobuf、Kryo、Hessian、Jackson 等,它们可以取代 Java 默认的序列化,从而提供更高效的性能。

为了支持高并发,传统的阻塞式 IO 显然不太合适,因此我们需要异步的 IO,即 NIO。Java 提供了 NIO 的解决方案,Java 7 也提供了更优秀的 NIO.2 支持,用 Java 实现 NIO 并不是遥不可及的事情,只是需要我们熟悉 NIO 的技术细节。

我们需要将服务部署在分布式环境下的不同节点上,通过服务注册的方式,让客户端来自动发现当前可用的服务,并调用这些服务。这需要一种服务注册表(Service Registry)的组件,让它来注册分布式环境下所有的服务地址(包括:主机名与端口号)。

每台 Server 上可发布多个 Service,这些 Service 共用一个 host 与 port,在分布式环境下会提供 Server 共同对外提供 Service。此外,为防止 Service Registry 出现单点故障,因此需要将其搭建为集群环境。


本文将为您揭晓开发轻量级分布式 RPC 框架的具体过程,该框架基于 TCP 协议,提供了 NIO 特性,提供高效的序列化方式,同时也具备服务注册与发现的能力。根据以上技术需求,我们可使用如下技术选型:

        Spring:它是最强大的依赖注入框架,也是业界的权威标准。

        Netty:它使 NIO 编程更加容易,屏蔽了 Java 底层的 NIO 细节。

        Protostuff:它基于 Protobuf 序列化框架,面向 POJO,无需编写 .proto 文件。

        ZooKeeper:提供服务注册与发现功能,开发分布式系统的必备选择,同时它也具备天生的集群能力。

1 第一步:编写服务接口


package com.lyz.zkrpc;

/**
* 定义服务接口
* @author liuyazhuang
*/
public interface HelloService {

String hello(String name);
}

将该接口放在独立的客户端 jar 包中,以供应用使用


2 第二步:编写服务接口的实现类

package com.lyz.zkrpc;

/**
* 实现服务接口
* @author liuyazhuang
*/
@RpcService(HelloService.class) // 指定远程接口
public class HelloServiceImpl implements HelloService {

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

使用RpcService注解定义在服务接口的实现类上,需要对该实现类指定远程接口,因为实现类可能会实现多个接口,一定要告诉框架哪个才是远程接口。


RpcService代码如下:


package com.lyz.zkrpc;
import org.springframework.stereotype.Component;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
* RPC接口注解
* @author liuyazhuang
*/
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Component // 标明可被 Spring 扫描
public @interface RpcService {

Class<?> value();
}

该注解具备 Spring 的Component注解的特性,可被 Spring 扫描。


该实现类放在服务端 jar 包中,该 jar 包还提供了一些服务端的配置文件与启动服务的引导程序。


3 第三步:配置服务端

服务端 Spring 配置文件名为spring-zk-rpc-server.xml,内容如下:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<!-- 配置自动扫包 -->
<context:component-scan base-package="com.lyz.zkrpc"/>
<context:property-placeholder location="classpath:rpc-server-config.properties"/>
<!-- 配置服务注册组件 -->
<bean id="serviceRegistry" class="com.lyz.zkrpc.ServiceRegistry">
<constructor-arg name="registryAddress" value="${registry.address}"/>
</bean>

<!-- 配置 RPC 服务器 -->
<bean id="rpcServer" class="com.lyz.zkrpc.RpcServer">
<constructor-arg name="serverAddress" value="${server.address}"/>
<constructor-arg name="serviceRegistry" ref="serviceRegistry"/>
</bean>
</beans>

具体的配置参数在rpc-server-config.properties文件中,内容如下:


<!-- lang: java -->
# ZooKeeper 服务器
registry.address=127.0.0.1:2181

# RPC 服务器
server.address=127.0.0.1:8000

以上配置表明:连接本地的 ZooKeeper 服务器,并在 8000 端口上发布 RPC 服务。


4 第四步:启动服务器并发布服务

为了加载 Spring 配置文件来发布服务,只需编写一个引导程序即可:


package com.lyz.zkrpc;

import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
* RPC服务启动入口
* @author liuyazhuang
*/
public class RpcBootstrap {

public static void main(String[] args) {
new ClassPathXmlApplicationContext("spring-zk-rpc-server.xml");
}
}

运行RpcBootstrap类的main方法即可启动服务端,但还有两个重要的组件尚未实现,它们分别是:

​ServiceRegistry与RpcServer​​,下文会给出具体实现细节。


5 第五步:实现服务注册

使用 ZooKeeper 客户端可轻松实现服务注册功能,ServiceRegistry代码如下:


package com.lyz.zkrpc;

import org.apache.zookeeper.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.concurrent.CountDownLatch;

/**
* 连接ZK注册中心,创建服务注册目录
* @author liuyazhuang
*/
public class ServiceRegistry {

private static final Logger LOGGER = LoggerFactory.getLogger(ServiceRegistry.class);

private CountDownLatch latch = new CountDownLatch(1);

private String registryAddress;

public ServiceRegistry(String registryAddress) {
this.registryAddress = registryAddress;
}

public void register(String data) {
if (data != null) {
ZooKeeper zk = connectServer();
if (zk != null) {
createNode(zk, data);
}
}
}

private ZooKeeper connectServer() {
ZooKeeper zk = null;
try {
zk = new ZooKeeper(registryAddress, Constant.ZK_SESSION_TIMEOUT, new Watcher() {
@Override
public void process(WatchedEvent event) {
// 判断是否已连接ZK,连接后计数器递减.
if (event.getState() == Event.KeeperState.SyncConnected) {
latch.countDown();
}
}
});

// 若计数器不为0,则等待.
latch.await();
} catch (IOException | InterruptedException e) {
LOGGER.error("", e);
}
return zk;
}

private void createNode(ZooKeeper zk, String data) {
try {
byte[] bytes = data.getBytes();
String path = zk.create(Constant.ZK_DATA_PATH, bytes, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
LOGGER.debug("create zookeeper node ({} => {})", path, data);
} catch (KeeperException | InterruptedException e) {
LOGGER.error("", e);
}
}
}

其中,通过Constant配置了所有的常量:


package com.lyz.zkrpc;

/**
* ZK相关常量
* @author liuyazhuang
*/
public interface Constant {

int ZK_SESSION_TIMEOUT = 5000;

String ZK_REGISTRY_PATH = "/registry";
String ZK_DATA_PATH = ZK_REGISTRY_PATH + "/data";
}

注意:首先需要使用 ZooKeeper 客户端命令行创建/registry永久节点,用于存放所有的服务临时节点。


6 第六步:实现 RPC 服务器

使用 Netty 可实现一个支持 NIO 的 RPC 服务器,需要使用ServiceRegistry注册服务地址,RpcServer代码如下:


package com.lyz.zkrpc;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import org.apache.commons.collections4.MapUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

import java.util.HashMap;
import java.util.Map;

/**
* 启动并注册服务
* @author liuyazhuang
*/
public class RpcServer implements ApplicationContextAware, InitializingBean {

private static final Logger LOGGER = LoggerFactory.getLogger(RpcServer.class);

private String serverAddress;
private ServiceRegistry serviceRegistry;

private Map<String, Object> handlerMap = new HashMap<String, Object>(); // 存放接口名与服务对象之间的映射关系

public RpcServer(String serverAddress) {
this.serverAddress = serverAddress;
}

public RpcServer(String serverAddress, ServiceRegistry serviceRegistry) {
this.serverAddress = serverAddress;
this.serviceRegistry = serviceRegistry;
}

@Override
public void setApplicationContext(ApplicationContext ctx) throws BeansException {
Map<String, Object> serviceBeanMap = ctx.getBeansWithAnnotation(RpcService.class); // 获取所有带有 RpcService 注解的 Spring Bean
if (MapUtils.isNotEmpty(serviceBeanMap)) {
for (Object serviceBean : serviceBeanMap.values()) {
String interfaceName = serviceBean.getClass().getAnnotation(RpcService.class).value().getName();
handlerMap.put(interfaceName, serviceBean);
}
}
}

@Override
public void afterPropertiesSet() throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel channel) throws Exception {
channel.pipeline()
.addLast(new RpcDecoder(RpcRequest.class)) // 将 RPC 请求进行解码(为了处理请求)
.addLast(new RpcEncoder(RpcResponse.class)) // 将 RPC 响应进行编码(为了返回响应)
.addLast(new RpcHandler(handlerMap)); // 处理 RPC 请求
}
})
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);

String[] array = serverAddress.split(":");
String host = array[0];
int port = Integer.parseInt(array[1]);

ChannelFuture future = bootstrap.bind(host, port).sync();
LOGGER.debug("server started on port {}", port);

if (serviceRegistry != null) {
serviceRegistry.register(serverAddress); // 注册服务地址
}

future.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
}
}
}

以上代码中,有两个重要的 POJO 需要描述一下,它们分别是RpcRequest与RpcResponse。


使用RpcRequest封装 RPC 请求,代码如下:


package com.lyz.zkrpc;

/**
* RPC请求
* @author liuyazhuang
*/
public class RpcRequest {

private String requestId;

private String className;

private String methodName;

private Class<?>[] parameterTypes;

private Object[] parameters;

public String getRequestId() {
return requestId;
}

public void setRequestId(String requestId) {
this.requestId = requestId;
}

public String getClassName() {
return className;
}

public void setClassName(String className) {
this.className = className;
}

public String getMethodName() {
return methodName;
}

public void setMethodName(String methodName) {
this.methodName = methodName;
}

public Class<?>[] getParameterTypes() {
return parameterTypes;
}

public void setParameterTypes(Class<?>[] parameterTypes) {
this.parameterTypes = parameterTypes;
}

public Object[] getParameters() {
return parameters;
}

public void setParameters(Object[] parameters) {
this.parameters = parameters;
}
}

使用RpcResponse封装 RPC 响应,代码如下:


package com.lyz.zkrpc;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.ByteToMessageDecoder;

import java.util.List;

/**
* RPC解码
* @author liuyazhuang
*/
public class RpcDecoder extends ByteToMessageDecoder {

private Class<?> genericClass;

public RpcDecoder(Class<?> genericClass) {
this.genericClass = genericClass;
}

@Override
public void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
if (in.readableBytes() < 4) {
return;
}
in.markReaderIndex();
int dataLength = in.readInt();
if (dataLength < 0) {
ctx.close();
}
if (in.readableBytes() < dataLength) {
in.resetReaderIndex();
return;
}
byte[] data = new byte[dataLength];
in.readBytes(data);

Object obj = SerializationUtil.deserialize(data, genericClass);
out.add(obj);
}
}

使用RpcEncoder提供 RPC 编码,只需扩展 Netty 的MessageToByteEncoder抽象类的encode方法即可,代码如下:


package com.lyz.zkrpc;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

/**
* RPC编码
* @author liuyazhuang
*/
public class RpcEncoder extends MessageToByteEncoder {

private Class<?> genericClass;

public RpcEncoder(Class<?> genericClass) {
this.genericClass = genericClass;
}

@Override
public void encode(ChannelHandlerContext ctx, Object in, ByteBuf out) throws Exception {
if (genericClass.isInstance(in)) {
byte[] data = SerializationUtil.serialize(in);
out.writeInt(data.length);
out.writeBytes(data);
}
}
}

编写一个SerializationUtil工具类,使用Protostuff实现序列化:


package com.lyz.zkrpc;

import com.dyuproject.protostuff.LinkedBuffer;
import com.dyuproject.protostuff.ProtostuffIOUtil;
import com.dyuproject.protostuff.Schema;
import com.dyuproject.protostuff.runtime.RuntimeSchema;
import org.objenesis.Objenesis;
import org.objenesis.ObjenesisStd;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
* Protostuff序列化与反序列化工具
* @author liuyazhuang
*/
public class SerializationUtil {

private static Map<Class<?>, Schema<?>> cachedSchema = new ConcurrentHashMap<>();

private static Objenesis objenesis = new ObjenesisStd(true);

private SerializationUtil() {
}

@SuppressWarnings("unchecked")
private static <T> Schema<T> getSchema(Class<T> cls) {
Schema<T> schema = (Schema<T>) cachedSchema.get(cls);
if (schema == null) {
schema = RuntimeSchema.createFrom(cls);
if (schema != null) {
cachedSchema.put(cls, schema);
}
}
return schema;
}

@SuppressWarnings("unchecked")
public static <T> byte[] serialize(T obj) {
Class<T> cls = (Class<T>) obj.getClass();
LinkedBuffer buffer = LinkedBuffer.allocate(LinkedBuffer.DEFAULT_BUFFER_SIZE);
try {
Schema<T> schema = getSchema(cls);
return ProtostuffIOUtil.toByteArray(obj, schema, buffer);
} catch (Exception e) {
throw new IllegalStateException(e.getMessage(), e);
} finally {
buffer.clear();
}
}

public static <T> T deserialize(byte[] data, Class<T> cls) {
try {
T message = (T) objenesis.newInstance(cls);
Schema<T> schema = getSchema(cls);
ProtostuffIOUtil.mergeFrom(data, message, schema);
return message;
} catch (Exception e) {
throw new IllegalStateException(e.getMessage(), e);
}
}
}

以上了使用 Objenesis 来实例化对象,它是比 Java 反射更加强大。


注意:如需要替换其它序列化框架,只需修改SerializationUtil即可。当然,更好的实现方式是提供配置项来决定使用哪种序列化方式。


使用RpcHandler中处理 RPC 请求,只需扩展 Netty 的SimpleChannelInboundHandler抽象类即可,代码如下:


package com.lyz.zkrpc;

import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import net.sf.cglib.reflect.FastClass;
import net.sf.cglib.reflect.FastMethod;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Map;

/**
* RPC服务端:请求处理过程
* @author liuyazhuang
*/
public class RpcHandler extends SimpleChannelInboundHandler<RpcRequest> {

private static final Logger LOGGER = LoggerFactory.getLogger(RpcHandler.class);

private final Map<String, Object> handlerMap;

public RpcHandler(Map<String, Object> handlerMap) {
this.handlerMap = handlerMap;
}

@Override
public void channelRead0(final ChannelHandlerContext ctx, RpcRequest request) throws Exception {
RpcResponse response = new RpcResponse();
response.setRequestId(request.getRequestId());
try {
Object result = handle(request);
response.setResult(result);
} catch (Throwable t) {
response.setError(t);
}
ctx.writeAndFlush(response).addListener(ChannelFutureListener.CLOSE);
}

private Object handle(RpcRequest request) throws Throwable {
String className = request.getClassName();
Object serviceBean = handlerMap.get(className);

Class<?> serviceClass = serviceBean.getClass();
String methodName = request.getMethodName();
Class<?>[] parameterTypes = request.getParameterTypes();
Object[] parameters = request.getParameters();

// Method method = serviceClass.getMethod(methodName, parameterTypes);
// method.setAccessible(true);
// return method.invoke(serviceBean, parameters);

FastClass serviceFastClass = FastClass.create(serviceClass);
FastMethod serviceFastMethod = serviceFastClass.getMethod(methodName, parameterTypes);
return serviceFastMethod.invoke(serviceBean, parameters);
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
LOGGER.error("server caught exception", cause);
ctx.close();
}
}

为了避免使用 Java 反射带来的性能问题,我们可以使用 CGLib 提供的反射 API,如上面用到的FastClass与FastMethod。


7 第七步:配置客户端

同样使用 Spring 配置文件来配置 RPC 客户端,spring-zk-rpc-client.xml代码如下:


<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<context:component-scan base-package="com.lyz.zkrpc"/>
<context:property-placeholder location="classpath:rpc-client-config.properties"/>
<!-- 配置服务发现组件 -->
<bean id="serviceDiscovery" class="com.lyz.zkrpc.ServiceDiscovery">
<constructor-arg name="registryAddress" value="${registry.address}"/>
</bean>
<!-- 配置 RPC 代理 -->
<bean id="rpcProxy" class="com.lyz.zkrpc.RpcProxy">
<constructor-arg name="serviceDiscovery" ref="serviceDiscovery"/>
</bean>
</beans>

其中rpc-client-config.properties提供了具体的配置:


<!-- lang: java -->
# ZooKeeper 服务器
registry.address=127.0.0.1:2181

8 第八步:实现服务发现

同样使用 ZooKeeper 实现服务发现功能,见如下代码:


package com.lyz.zkrpc;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ThreadLocalRandom;

/**
* 服务发现:连接ZK,添加watch事件
* @author liuyazhuang
*/
public class ServiceDiscovery {

private static final Logger LOGGER = LoggerFactory.getLogger(ServiceDiscovery.class);

private CountDownLatch latch = new CountDownLatch(1);

private volatile List<String> dataList = new ArrayList<>();

private String registryAddress;

public ServiceDiscovery(String registryAddress) {
this.registryAddress = registryAddress;

ZooKeeper zk = connectServer();
if (zk != null) {
watchNode(zk);
}
}

public String discover() {
String data = null;
int size = dataList.size();
if (size > 0) {
if (size == 1) {
data = dataList.get(0);
LOGGER.debug("using only data: {}", data);
} else {
data = dataList.get(ThreadLocalRandom.current().nextInt(size));
LOGGER.debug("using random data: {}", data);
}
}
return data;
}

private ZooKeeper connectServer() {
ZooKeeper zk = null;
try {
zk = new ZooKeeper(registryAddress, Constant.ZK_SESSION_TIMEOUT, new Watcher() {
@Override
public void process(WatchedEvent event) {
if (event.getState() == Event.KeeperState.SyncConnected) {
latch.countDown();
}
}
});
latch.await();
} catch (IOException | InterruptedException e) {
LOGGER.error("", e);
}
return zk;
}

private void watchNode(final ZooKeeper zk) {
try {
List<String> nodeList = zk.getChildren(Constant.ZK_REGISTRY_PATH, new Watcher() {
@Override
public void process(WatchedEvent event) {
if (event.getType() == Event.EventType.NodeChildrenChanged) {
watchNode(zk);
}
}
});
List<String> dataList = new ArrayList<>();
for (String node : nodeList) {
byte[] bytes = zk.getData(Constant.ZK_REGISTRY_PATH + "/" + node, false, null);
dataList.add(new String(bytes));
}
LOGGER.debug("node data: {}", dataList);
this.dataList = dataList;
} catch (KeeperException | InterruptedException e) {
LOGGER.error("", e);
}
}
}

9 第九步:实现 RPC 代理

这里使用 Java 提供的动态代理技术实现 RPC 代理(当然也可以使用 CGLib 来实现),具体代码如下:


package com.lyz.zkrpc;

import net.sf.cglib.proxy.InvocationHandler;
import net.sf.cglib.proxy.Proxy;

import java.lang.reflect.Method;
import java.util.UUID;

/**
* 客户端RPC调用代理
* @author liuyazhuang
*/
public class RpcProxy {

private String serverAddress;
private ServiceDiscovery serviceDiscovery;

public RpcProxy(String serverAddress) {
this.serverAddress = serverAddress;
}

public RpcProxy(ServiceDiscovery serviceDiscovery) {
this.serviceDiscovery = serviceDiscovery;
}

@SuppressWarnings("unchecked")
public <T> T create(Class<?> interfaceClass) {
return (T) Proxy.newProxyInstance(
interfaceClass.getClassLoader(),
new Class<?>[]{interfaceClass},
new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
RpcRequest request = new RpcRequest(); // 创建并初始化 RPC 请求
request.setRequestId(UUID.randomUUID().toString());
request.setClassName(method.getDeclaringClass().getName());
request.setMethodName(method.getName());
request.setParameterTypes(method.getParameterTypes());
request.setParameters(args);

if (serviceDiscovery != null) {
serverAddress = serviceDiscovery.discover(); // 发现服务
}

String[] array = serverAddress.split(":");
String host = array[0];
int port = Integer.parseInt(array[1]);

RpcClient client = new RpcClient(host, port); // 初始化 RPC 客户端
RpcResponse response = client.send(request); // 通过 RPC 客户端发送 RPC 请求并获取 RPC 响应

if (response.getError() != null) {
throw response.getError();
} else {
return response.getResult();
}
}
}
);
}
}

使用RpcClient类实现 RPC 客户端,只需扩展 Netty 提供的SimpleChannelInboundHandler抽象类即可,代码如下:


package com.lyz.zkrpc;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
* RPC真正调用客户端
* @author liuyazhuang
*/
public class RpcClient extends SimpleChannelInboundHandler<RpcResponse> {

private static final Logger LOGGER = LoggerFactory.getLogger(RpcClient.class);

private String host;
private int port;

private RpcResponse response;

private final Object obj = new Object();

public RpcClient(String host, int port) {
this.host = host;
this.port = port;
}

@Override
public void channelRead0(ChannelHandlerContext ctx, RpcResponse response) throws Exception {
this.response = response;

synchronized (obj) {
obj.notifyAll(); // 收到响应,唤醒线程
}
}

@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
LOGGER.error("client caught exception", cause);
ctx.close();
}

public RpcResponse send(RpcRequest request) throws Exception {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group).channel(NioSocketChannel.class)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel channel) throws Exception {
channel.pipeline()
.addLast(new RpcEncoder(RpcRequest.class)) // 将 RPC 请求进行编码(为了发送请求)
.addLast(new RpcDecoder(RpcResponse.class)) // 将 RPC 响应进行解码(为了处理响应)
.addLast(RpcClient.this); // 使用 RpcClient 发送 RPC 请求
}
})
.option(ChannelOption.SO_KEEPALIVE, true);

ChannelFuture future = bootstrap.connect(host, port).sync();
future.channel().writeAndFlush(request).sync();

synchronized (obj) {
obj.wait(); // 未收到响应,使线程等待
}

if (response != null) {
future.channel().closeFuture().sync();
}
return response;
} finally {
group.shutdownGracefully();
}
}
}

10 第十步:发送 RPC 请求

使用 JUnit 结合 Spring 编写一个单元测试,代码如下:


<!-- lang: java -->
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:spring.xml")
/**
* 测试RPC服务
* @author liuyazhuang
*/
public class HelloServiceTest {

@Autowired
private RpcProxy rpcProxy;

@Test
public void helloTest() {
HelloService helloService = rpcProxy.create(HelloService.class);
String result = helloService.hello("World");
Assert.assertEquals("Hello! World", result);
}
}

11 最后,总结

本文通过 Spring + Netty + Protostuff + ZooKeeper 实现了一个轻量级 RPC 框架,使用 Spring 提供依赖注入与参数配置,使用 Netty 实现 NIO 方式的数据传输,使用 Protostuff 实现对象序列化,使用 ZooKeeper 实现服务注册与发现。使用该框架,可将服务部署到分布式环境中的任意节点上,客户端通过远程接口来调用服务端的具体实现,让服务端与客户端的开发完全分离,为实现大规模分布式应用提供了基础支持。


12 附录:Maven 依赖

<!-- lang: xml -->
<!-- JUnit -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.11</version>
<scope>test</scope>
</dependency>

<!-- SLF4J -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.7</version>
</dependency>

<!-- Spring -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>3.2.12.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-test</artifactId>
<version>3.2.12.RELEASE</version>
<scope>test</scope>
</dependency>

<!-- Netty -->
<dependency>
<groupId>io.netty</groupId>
<artifactId>netty-all</artifactId>
<version>4.0.24.Final</version>
</dependency>

<!-- Protostuff -->
<dependency>
<groupId>com.dyuproject.protostuff</groupId>
<artifactId>protostuff-core</artifactId>
<version>1.0.8</version>
</dependency>
<dependency>
<groupId>com.dyuproject.protostuff</groupId>
<artifactId>protostuff-runtime</artifactId>
<version>1.0.8</version>
</dependency>

<!-- ZooKeeper -->
<dependency>
<groupId>org.apache.zookeeper</groupId>
<artifactId>zookeeper</artifactId>
<version>3.4.6</version>
</dependency>

<!-- Apache Commons Collections -->
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-collections4</artifactId>
<version>4.0</version>
</dependency>

<!-- Objenesis -->
<dependency>
<groupId>org.objenesis</groupId>
<artifactId>objenesis</artifactId>
<version>2.1</version>
</dependency>

<!-- CGLib -->
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.1</version>
</dependency>

13 分布式RPC流程图


RPC之——轻量级分布式RPC框架实战_分布式

RPC之——轻量级分布式RPC框架实战_RPC_02