開發SpringCloud微服務三年,我才知道@EnableEurekaServer注解到底做了什麼（上）

全是幹貨的 Java 技術倉庫：

• https://github.com/Wasabi1234/Java-Interview-Tutorial
• 服務注冊發現示意圖

• 

• 當你在啟動類上添加了啟動 Eureka 服務注冊中心注解時，到底發生了什麼呢？

• 

• 激活eureka伺服器相關配置EurekaServerAutoConfiguration的注解

• 

• EurekaServerMarkerConfiguration

• 

• 點選到這裡，我們發現 spring.factories檔案

• 

• 注意到如下注解

• 

  ​​​​

@ConditionalOnBean - 條件注入

也就是當有EurekaServerMarkerConfiguration.Marker.class時，才會注入

是以@EnableEurekaServer就是個開關，隻要寫了該注解，spring 就會幫你把

EurekaServerAutoConfiguration類注入進來。

那麼為什麼注入他就行了？

EurekaServerAutoConfiguration#jerseyFilterRegistration

注意如下類：

ApplicationResource#addInstance

相當于 MVC 中的 controller

/**
     * Registers information about a particular instance for an
     * {@link com.netflix.discovery.shared.Application}.
     *
     * @param info
     *            {@link InstanceInfo} information of the instance.
     * @param isReplication
     *            a header parameter containing information whether this is
     *            replicated from other nodes.
     */
    @POST
    @Consumes({"application/json", "application/xml"})
    public Response addInstance(InstanceInfo info,
                                @HeaderParam(PeerEurekaNode.HEADER_REPLICATION) String isReplication) {
        logger.debug("Registering instance {} (replication={})", info.getId(), isReplication);
        // validate that the instanceinfo contains all the necessary required fields
        if (isBlank(info.getId())) {
            return Response.status(400).entity("Missing instanceId").build();
        } else if (isBlank(info.getHostName())) {
            return Response.status(400).entity("Missing hostname").build();
        } else if (isBlank(info.getIPAddr())) {
            return Response.status(400).entity("Missing ip address").build();
        } else if (isBlank(info.getAppName())) {
            return Response.status(400).entity("Missing appName").build();
        } else if (!appName.equals(info.getAppName())) {
            return Response.status(400).entity("Mismatched appName, expecting " + appName + " but was " + info.getAppName()).build();
        } else if (info.getDataCenterInfo() == null) {
            return Response.status(400).entity("Missing dataCenterInfo").build();
        } else if (info.getDataCenterInfo().getName() == null) {
            return Response.status(400).entity("Missing dataCenterInfo Name").build();
        }

        // handle cases where clients may be registering with bad DataCenterInfo with missing data
        DataCenterInfo dataCenterInfo = info.getDataCenterInfo();
        if (dataCenterInfo instanceof UniqueIdentifier) {
            String dataCenterInfoId = ((UniqueIdentifier) dataCenterInfo).getId();
            if (isBlank(dataCenterInfoId)) {
                boolean experimental = "true".equalsIgnoreCase(serverConfig.getExperimental("registration.validation.dataCenterInfoId"));
                if (experimental) {
                    String entity = "DataCenterInfo of type " + dataCenterInfo.getClass() + " must contain a valid id";
                    return Response.status(400).entity(entity).build();
                } else if (dataCenterInfo instanceof AmazonInfo) {
                    AmazonInfo amazonInfo = (AmazonInfo) dataCenterInfo;
                    String effectiveId = amazonInfo.get(AmazonInfo.MetaDataKey.instanceId);
                    if (effectiveId == null) {
                        amazonInfo.getMetadata().put(AmazonInfo.MetaDataKey.instanceId.getName(), info.getId());
                    }
                } else {
                    logger.warn("Registering DataCenterInfo of type {} without an appropriate id", dataCenterInfo.getClass());
                }
            }
        }

        registry.register(info, "true".equals(isReplication));
        return Response.status(204).build();  // 204 to be backwards compatible
    }      

注意如下繼承體系圖