摘要：前言基于表單的遠(yuǎn)程調(diào)用協(xié)議，采用的實(shí)現(xiàn)，關(guān)于協(xié)議就不用多說了吧。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)議的部分，內(nèi)容比較簡單，可以參考著官方文檔了解一下。

目標(biāo)：介紹遠(yuǎn)程調(diào)用中跟http協(xié)議相關(guān)的設(shè)計(jì)和實(shí)現(xiàn)，介紹dubbo-rpc-http的源碼。

基于HTTP表單的遠(yuǎn)程調(diào)用協(xié)議，采用 Spring 的HttpInvoker實(shí)現(xiàn)，關(guān)于http協(xié)議就不用多說了吧。

該類繼承了RemoteInvocation類，是在RemoteInvocation上增加了泛化調(diào)用的參數(shù)設(shè)置，以及增加了dubbo本身需要的附加值設(shè)置。

public class HttpRemoteInvocation extends RemoteInvocation {

    private static final long serialVersionUID = 1L;
    /**
     * dubbo的附加值名稱
     */
    private static final String dubboAttachmentsAttrName = "dubbo.attachments";

    public HttpRemoteInvocation(MethodInvocation methodInvocation) {
        super(methodInvocation);
        // 把附加值加入到會(huì)話域的屬性里面
        addAttribute(dubboAttachmentsAttrName, new HashMap(RpcContext.getContext().getAttachments()));
    }

    @Override
    public Object invoke(Object targetObject) throws NoSuchMethodException, IllegalAccessException,
            InvocationTargetException {
        // 獲得上下文
        RpcContext context = RpcContext.getContext();
        // 獲得附加值
        context.setAttachments((Map) getAttribute(dubboAttachmentsAttrName));

        // 泛化標(biāo)志
        String generic = (String) getAttribute(Constants.GENERIC_KEY);
        // 如果不為空，則設(shè)置泛化標(biāo)志
        if (StringUtils.isNotEmpty(generic)) {
            context.setAttachment(Constants.GENERIC_KEY, generic);
        }
        try {
            // 調(diào)用下一個(gè)調(diào)用鏈
            return super.invoke(targetObject);
        } finally {
            context.setAttachments(null);

        }
    }
}

該類是http實(shí)現(xiàn)的核心，跟我在《dubbo源碼解析（二十五）遠(yuǎn)程調(diào)用——hessian協(xié)議》中講到的HessianProtocol實(shí)現(xiàn)有很多地方相似。

/**
 * 默認(rèn)的端口號(hào)
 */
public static final int DEFAULT_PORT = 80;

/**
 * http服務(wù)器集合
 */
private final Map serverMap = new ConcurrentHashMap();

/**
 * Spring HttpInvokerServiceExporter 集合
 */
private final Map skeletonMap = new ConcurrentHashMap();

/**
 * HttpBinder對(duì)象
 */
private HttpBinder httpBinder;

@Override
protected  Runnable doExport(final T impl, Class type, URL url) throws RpcException {
    // 獲得ip地址
    String addr = getAddr(url);
    // 獲得http服務(wù)器
    HttpServer server = serverMap.get(addr);
    // 如果服務(wù)器為空，則重新創(chuàng)建服務(wù)器，并且加入到集合
    if (server == null) {
        server = httpBinder.bind(url, new InternalHandler());
        serverMap.put(addr, server);
    }

    // 獲得服務(wù)path
    final String path = url.getAbsolutePath();

    // 加入集合
    skeletonMap.put(path, createExporter(impl, type));

    // 通用path
    final String genericPath = path + "/" + Constants.GENERIC_KEY;

    // 添加泛化的服務(wù)調(diào)用
    skeletonMap.put(genericPath, createExporter(impl, GenericService.class));
    return new Runnable() {
        @Override
        public void run() {
            skeletonMap.remove(path);
            skeletonMap.remove(genericPath);
        }
    };
}

該方法是暴露服務(wù)等邏輯，因?yàn)閐ubbo實(shí)現(xiàn)http協(xié)議采用了Spring 的HttpInvoker實(shí)現(xiàn)，所以調(diào)用了createExporter方法來創(chuàng)建創(chuàng)建HttpInvokerServiceExporter。

private  HttpInvokerServiceExporter createExporter(T impl, Class type) {
    // 創(chuàng)建HttpInvokerServiceExporter
    final HttpInvokerServiceExporter httpServiceExporter = new HttpInvokerServiceExporter();
    // 設(shè)置要訪問的服務(wù)的接口
    httpServiceExporter.setServiceInterface(type);
    // 設(shè)置服務(wù)實(shí)現(xiàn)
    httpServiceExporter.setService(impl);
    try {
        // 在BeanFactory設(shè)置了所有提供的bean屬性，初始化bean的時(shí)候執(zhí)行，可以針對(duì)某個(gè)具體的bean進(jìn)行配
        httpServiceExporter.afterPropertiesSet();
    } catch (Exception e) {
        throw new RpcException(e.getMessage(), e);
    }
    return httpServiceExporter;
}

該方法是創(chuàng)建一個(gè)spring 的HttpInvokerServiceExporter。

@Override
@SuppressWarnings("unchecked")
protected  T doRefer(final Class serviceType, final URL url) throws RpcException {
    // 獲得泛化配置
    final String generic = url.getParameter(Constants.GENERIC_KEY);
    // 是否為泛化調(diào)用
    final boolean isGeneric = ProtocolUtils.isGeneric(generic) || serviceType.equals(GenericService.class);

    // 創(chuàng)建HttpInvokerProxyFactoryBean
    final HttpInvokerProxyFactoryBean httpProxyFactoryBean = new HttpInvokerProxyFactoryBean();
    // 設(shè)置RemoteInvocation的工廠類
    httpProxyFactoryBean.setRemoteInvocationFactory(new RemoteInvocationFactory() {
        /**
         * 為給定的AOP方法調(diào)用創(chuàng)建一個(gè)新的RemoteInvocation對(duì)象。
         * @param methodInvocation
         * @return
         */
        @Override
        public RemoteInvocation createRemoteInvocation(MethodInvocation methodInvocation) {
            // 新建一個(gè)HttpRemoteInvocation
            RemoteInvocation invocation = new HttpRemoteInvocation(methodInvocation);
            // 如果是泛化調(diào)用
            if (isGeneric) {
                // 設(shè)置標(biāo)志
                invocation.addAttribute(Constants.GENERIC_KEY, generic);
            }
            return invocation;
        }
    });
    // 獲得identity message
    String key = url.toIdentityString();
    // 如果是泛化調(diào)用
    if (isGeneric) {
        key = key + "/" + Constants.GENERIC_KEY;
    }
    // 設(shè)置服務(wù)url
    httpProxyFactoryBean.setServiceUrl(key);
    // 設(shè)置服務(wù)接口
    httpProxyFactoryBean.setServiceInterface(serviceType);
    // 獲得客戶端參數(shù)
    String client = url.getParameter(Constants.CLIENT_KEY);
    if (client == null || client.length() == 0 || "simple".equals(client)) {
        // 創(chuàng)建SimpleHttpInvokerRequestExecutor連接池 使用的是JDK HttpClient
        SimpleHttpInvokerRequestExecutor httpInvokerRequestExecutor = new SimpleHttpInvokerRequestExecutor() {
            @Override
            protected void prepareConnection(HttpURLConnection con,
                                             int contentLength) throws IOException {
                super.prepareConnection(con, contentLength);
                // 設(shè)置讀取超時(shí)時(shí)間
                con.setReadTimeout(url.getParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT));
                // 設(shè)置連接超時(shí)時(shí)間
                con.setConnectTimeout(url.getParameter(Constants.CONNECT_TIMEOUT_KEY, Constants.DEFAULT_CONNECT_TIMEOUT));
            }
        };
        httpProxyFactoryBean.setHttpInvokerRequestExecutor(httpInvokerRequestExecutor);
    } else if ("commons".equals(client)) {
        // 創(chuàng)建 HttpComponentsHttpInvokerRequestExecutor連接池 使用的是Apache HttpClient
        HttpComponentsHttpInvokerRequestExecutor httpInvokerRequestExecutor = new HttpComponentsHttpInvokerRequestExecutor();
        // 設(shè)置讀取超時(shí)時(shí)間
        httpInvokerRequestExecutor.setReadTimeout(url.getParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT));
        // 設(shè)置連接超時(shí)時(shí)間
        httpInvokerRequestExecutor.setConnectTimeout(url.getParameter(Constants.CONNECT_TIMEOUT_KEY, Constants.DEFAULT_CONNECT_TIMEOUT));
        httpProxyFactoryBean.setHttpInvokerRequestExecutor(httpInvokerRequestExecutor);
    } else {
        throw new IllegalStateException("Unsupported http protocol client " + client + ", only supported: simple, commons");
    }
    httpProxyFactoryBean.afterPropertiesSet();
    // 返回HttpInvokerProxyFactoryBean對(duì)象
    return (T) httpProxyFactoryBean.getObject();
}

該方法是服務(wù)引用的方法，其中根據(jù)url配置simple還是commons來選擇創(chuàng)建連接池的方式。其中的區(qū)別就是SimpleHttpInvokerRequestExecutor使用的是JDK HttpClient，HttpComponentsHttpInvokerRequestExecutor 使用的是Apache HttpClient。

@Override
protected int getErrorCode(Throwable e) {
    if (e instanceof RemoteAccessException) {
        e = e.getCause();
    }
    if (e != null) {
        Class cls = e.getClass();
        if (SocketTimeoutException.class.equals(cls)) {
            // 返回超時(shí)異常
            return RpcException.TIMEOUT_EXCEPTION;
        } else if (IOException.class.isAssignableFrom(cls)) {
            // 返回網(wǎng)絡(luò)異常
            return RpcException.NETWORK_EXCEPTION;
        } else if (ClassNotFoundException.class.isAssignableFrom(cls)) {
            // 返回序列化異常
            return RpcException.SERIALIZATION_EXCEPTION;
        }
    }
    return super.getErrorCode(e);
}

該方法是處理異常情況，設(shè)置錯(cuò)誤碼。

private class InternalHandler implements HttpHandler {

    @Override
    public void handle(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        // 獲得請(qǐng)求uri
        String uri = request.getRequestURI();
        // 獲得服務(wù)暴露者HttpInvokerServiceExporter對(duì)象
        HttpInvokerServiceExporter skeleton = skeletonMap.get(uri);
        // 如果不是post，則返回碼設(shè)置500
        if (!request.getMethod().equalsIgnoreCase("POST")) {
            response.setStatus(500);
        } else {
            // 遠(yuǎn)程地址放到上下文
            RpcContext.getContext().setRemoteAddress(request.getRemoteAddr(), request.getRemotePort());
            try {
                // 調(diào)用下一個(gè)調(diào)用
                skeleton.handleRequest(request, response);
            } catch (Throwable e) {
                throw new ServletException(e);
            }
        }
    }

}

該內(nèi)部類實(shí)現(xiàn)了HttpHandler，做了設(shè)置遠(yuǎn)程地址的邏輯。

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http協(xié)議的部分，內(nèi)容比較簡單，可以參考著官方文檔了解一下。接下來我將開始對(duì)rpc模塊關(guān)于injvm本地調(diào)用部分進(jìn)行講解。