远程调用——memcached协议目标：介绍memcached协议的设计和实现，介绍dubbo-rpc-memcached的源码。前言dubbo实现memcached协议是基于Memcached，Memcached 是一个高效的 KV 缓存服务器，在dubbo中没有涉及到关于memcached协议的服务暴露，只有服务引用，因为在访问Memcached服务器时，Memcached客户端可以在服务器上存储也可以获取。源码分析（一）MemcachedProtocol该类继承AbstractProtocol，是memcached协议实现的核心。1.属性/** * 默认端口号 */public static final int DEFAULT_PORT = 11211;2.export@Overridepublic <T> Exporter<T> export(final Invoker<T> invoker) throws RpcException { // 不支持memcached服务暴露 throw new UnsupportedOperationException(“Unsupported export memcached service. url: " + invoker.getUrl());}可以看到，服务暴露方法直接抛出异常。3.refer@Overridepublic <T> Invoker<T> refer(final Class<T> type, final URL url) throws RpcException { try { // 获得地址 String address = url.getAddress(); // 获得备用地址 String backup = url.getParameter(Constants.BACKUP_KEY); // 把备用地址拼接上 if (backup != null && backup.length() > 0) { address += “,” + backup; } // 创建Memcached客户端构造器 MemcachedClientBuilder builder = new XMemcachedClientBuilder(AddrUtil.getAddresses(address)); // 创建客户端 final MemcachedClient memcachedClient = builder.build(); // 到期时间参数配置 final int expiry = url.getParameter(“expiry”, 0); // 获得值命令 final String get = url.getParameter(“get”, “get”); // 添加值命令根据类型来取决是put还是set final String set = url.getParameter(“set”, Map.class.equals(type) ? “put” : “set”); // 删除值命令 final String delete = url.getParameter(“delete”, Map.class.equals(type) ? “remove” : “delete”); return new AbstractInvoker<T>(type, url) { @Override protected Result doInvoke(Invocation invocation) throws Throwable { try { // 如果是获取方法名的值 if (get.equals(invocation.getMethodName())) { // 如果参数长度不等于1，则抛出异常 if (invocation.getArguments().length != 1) { throw new IllegalArgumentException(“The memcached get method arguments mismatch, must only one arguments. interface: " + type.getName() + “, method: " + invocation.getMethodName() + “, url: " + url); } // 否则调用get方法来获取 return new RpcResult(memcachedClient.get(String.valueOf(invocation.getArguments()[0]))); } else if (set.equals(invocation.getMethodName())) { // 如果参数长度不为2，则抛出异常 if (invocation.getArguments().length != 2) { throw new IllegalArgumentException(“The memcached set method arguments mismatch, must be two arguments. interface: " + type.getName() + “, method: " + invocation.getMethodName() + “, url: " + url); } // 无论任何现有值如何，都在缓存中设置一个对象 memcachedClient.set(String.valueOf(invocation.getArguments()[0]), expiry, invocation.getArguments()[1]); return new RpcResult(); } else if (delete.equals(invocation.getMethodName())) { // 删除操作只有一个参数，如果参数长度不等于1，则抛出异常 if (invocation.getArguments().length != 1) { throw new IllegalArgumentException(“The memcached delete method arguments mismatch, must only one arguments. interface: " + type.getName() + “, method: " + invocation.getMethodName() + “, url: " + url); } // 删除某个值 memcachedClient.delete(String.valueOf(invocation.getArguments()[0])); return new RpcResult(); } else { // 不支持的操作 throw new UnsupportedOperationException(“Unsupported method " + invocation.getMethodName() + " in memcached service.”); } } catch (Throwable t) { RpcException re = new RpcException(“Failed to invoke memcached service method. interface: " + type.getName() + “, method: " + invocation.getMethodName() + “, url: " + url + “, cause: " + t.getMessage(), t); if (t instanceof TimeoutException || t instanceof SocketTimeoutException) { re.setCode(RpcException.TIMEOUT_EXCEPTION); } else if (t instanceof MemcachedException || t instanceof IOException) { re.setCode(RpcException.NETWORK_EXCEPTION); } throw re; } } @Override public void destroy() { super.destroy(); try { // 关闭客户端 memcachedClient.shutdown(); } catch (Throwable e) { logger.warn(e.getMessage(), e); } } }; } catch (Throwable t) { throw new RpcException(“Failed to refer memcached service. interface: " + type.getName() + “, url: " + url + “, cause: " + t.getMessage(), t); }}该方法是服务引用方法，基于MemcachedClient的get、set、delete方法来对应Memcached的get、set、delete命令进行对值的操作。后记该部分相关的源码解析地址：https://github.com/CrazyHZM/i…该文章讲解了远程调用中关于memcached协议实现的部分，逻辑比较简单。接下来我将开始对rpc模块关于redis协议部分进行讲解。
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