摘要：源碼分析一該類(lèi)繼承，是協(xié)議實(shí)現(xiàn)的核心。屬性默認(rèn)端口號(hào)不支持服務(wù)暴露可以看到，服務(wù)暴露方法直接拋出異常。后記該部分相關(guān)的源碼解析地址該文章講解了遠(yuǎn)程調(diào)用中關(guān)于協(xié)議實(shí)現(xiàn)的部分，邏輯比較簡(jiǎn)單。

目標(biāo)：介紹memcached協(xié)議的設(shè)計(jì)和實(shí)現(xiàn)，介紹dubbo-rpc-memcached的源碼。

dubbo實(shí)現(xiàn)memcached協(xié)議是基于Memcached，Memcached 是一個(gè)高效的 KV 緩存服務(wù)器，在dubbo中沒(méi)有涉及到關(guān)于memcached協(xié)議的服務(wù)暴露，只有服務(wù)引用，因?yàn)樵谠L問(wèn)Memcached服務(wù)器時(shí)，Memcached客戶(hù)端可以在服務(wù)器上存儲(chǔ)也可以獲取。

該類(lèi)繼承AbstractProtocol，是memcached協(xié)議實(shí)現(xiàn)的核心。

/**
 * 默認(rèn)端口號(hào)
 */
public static final int DEFAULT_PORT = 11211;

@Override
public  Exporter export(final Invoker invoker) throws RpcException {
    // 不支持memcached服務(wù)暴露
    throw new UnsupportedOperationException("Unsupported export memcached service. url: " + invoker.getUrl());
}

可以看到，服務(wù)暴露方法直接拋出異常。

@Override
public  Invoker refer(final Class type, final URL url) throws RpcException {
    try {
        // 獲得地址
        String address = url.getAddress();
        // 獲得備用地址
        String backup = url.getParameter(Constants.BACKUP_KEY);
        // 把備用地址拼接上
        if (backup != null && backup.length() > 0) {
            address += "," + backup;
        }
        // 創(chuàng)建Memcached客戶(hù)端構(gòu)造器
        MemcachedClientBuilder builder = new XMemcachedClientBuilder(AddrUtil.getAddresses(address));
        // 創(chuàng)建客戶(hù)端
        final MemcachedClient memcachedClient = builder.build();
        // 到期時(shí)間參數(shù)配置
        final int expiry = url.getParameter("expiry", 0);
        // 獲得值命令
        final String get = url.getParameter("get", "get");
        // 添加值命令根據(jù)類(lèi)型來(lái)取決是put還是set
        final String set = url.getParameter("set", Map.class.equals(type) ? "put" : "set");
        // 刪除值命令
        final String delete = url.getParameter("delete", Map.class.equals(type) ? "remove" : "delete");
        return new AbstractInvoker(type, url) {
            @Override
            protected Result doInvoke(Invocation invocation) throws Throwable {
                try {
                    // 如果是獲取方法名的值
                    if (get.equals(invocation.getMethodName())) {
                        // 如果參數(shù)長(zhǎng)度不等于1，則拋出異常
                        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);
                        }
                        // 否則調(diào)用get方法來(lái)獲取
                        return new RpcResult(memcachedClient.get(String.valueOf(invocation.getArguments()[0])));
                    } else if (set.equals(invocation.getMethodName())) {
                        // 如果參數(shù)長(zhǎng)度不為2，則拋出異常
                        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);
                        }
                        // 無(wú)論任何現(xiàn)有值如何，都在緩存中設(shè)置一個(gè)對(duì)象
                        memcachedClient.set(String.valueOf(invocation.getArguments()[0]), expiry, invocation.getArguments()[1]);
                        return new RpcResult();
                    } else if (delete.equals(invocation.getMethodName())) {
                        // 刪除操作只有一個(gè)參數(shù)，如果參數(shù)長(zhǎng)度不等于1，則拋出異常
                        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);
                        }
                        // 刪除某個(gè)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 {
                    // 關(guān)閉客戶(hù)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);
    }
}

該方法是服務(wù)引用方法，基于MemcachedClient的get、set、delete方法來(lái)對(duì)應(yīng)Memcached的get、set、delete命令進(jìn)行對(duì)值的操作。

該部分相關(guān)的源碼解析地址：https://github.com/CrazyHZM/i...

該文章講解了遠(yuǎn)程調(diào)用中關(guān)于memcached協(xié)議實(shí)現(xiàn)的部分，邏輯比較簡(jiǎn)單。接下來(lái)我將開(kāi)始對(duì)rpc模塊關(guān)于redis協(xié)議部分進(jìn)行講解。