SpringCloud源码分析（一）--注册中心搭建

一、前言

目前微服务可以说相当的火，很多公司都开始了拥抱互联网，都开始采用或者计划采用微服务，不管是国内阿里巴巴的开源的dubbo还是spring cloud都是微服务开发中的翘楚，为微服务的流行提供了很好的平台，减少了技术壁垒，就如当年spring兴起一样。本篇系列文章主要记录自己在学习spring cloud过程中的一些知识，包括一些用法、源码解析，作为自己学习记录和知识的总结。但是自己能力有限，不可避免出现各种问题或者理解不对的地方，希望各位可以多多指教。

二、使用的版本

spring cloud的全家桶包括的内容很多，得益于各个社区的支持，其对应的版本更新的也比较快，它是基于spring boot的，本文使用相对较新的spring boot版本是2.0.6.RELEASE，配套的spring-cloud的版本是Finchley.SR1。很有可能各个版本的源码逻辑不太一致。

三、spring cloud的搭建

1、各位可以自行参靠如何搭建spring boot的工程。

2、pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zxy.springcloud</groupId>
    <artifactId>eurekaserver</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>eurekaserver</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.SR1</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>


</project>

3、运行工程

在启动类上加上一个注解@EnableEurekaServer，启动工程就可以将此工程作为一个服务注册中心了，无需添加任何配置

@SpringBootApplication
@EnableEurekaServer
public class EurekaserverApplication {

    public static void main(String[] args) {
        SpringApplication.run(EurekaserverApplication.class, args);
    }
}

4、程序出错

在运行过程中，控制台报了错误

com.sun.jersey.api.client.ClientHandlerException: java.net.ConnectException: Connection refused: connect
    at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.filter.GZIPContentEncodingFilter.handle(GZIPContentEncodingFilter.java:123) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.sun.jersey.api.client.Client.handle(Client.java:652) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.WebResource.handle(WebResource.java:682) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.WebResource$Builder.post(WebResource.java:570) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.netflix.discovery.shared.transport.jersey.AbstractJerseyEurekaHttpClient.register(AbstractJerseyEurekaHttpClient.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.MetricsCollectingEurekaHttpClient.execute(MetricsCollectingEurekaHttpClient.java:73) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.executeOnNewServer(RedirectingEurekaHttpClient.java:118) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.execute(RedirectingEurekaHttpClient.java:79) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:120) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.3.jar:1.9.3]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_144]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_144]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_144]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_144]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_144]
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method) ~[na:1.8.0_144]
    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85) ~[na:1.8.0_144]
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_144]
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_144]
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_144]
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) ~[na:1.8.0_144]
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_144]
    at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_144]
    at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:121) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56) ~[httpclient-4.5.6.jar:4.5.6]
    at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
    ... 30 common frames omitted

2018-11-11 16:40:48.334  WARN 9788 --- [nfoReplicator-0] c.n.d.s.t.d.RetryableEurekaHttpClient    : Request execution failed with message: java.net.ConnectException: Connection refused: connect
2018-11-11 16:40:48.334  WARN 9788 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_UNKNOWN/DESKTOP-SMANTUI.mshome.net - registration failed Cannot execute request on any known server

com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
    at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.3.jar:1.9.3]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_144]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_144]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_144]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_144]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_144]

2018-11-11 16:40:48.334  WARN 9788 --- [nfoReplicator-0] c.n.discovery.InstanceInfoReplicator     : There was a problem with the instance info replicator

com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
    at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.3.jar:1.9.3]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_144]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_144]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_144]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_144]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_144]

2018-11-11 16:41:16.117  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Disable delta property : false
2018-11-11 16:41:16.118  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Single vip registry refresh property : null
2018-11-11 16:41:16.118  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Force full registry fetch : false
2018-11-11 16:41:16.118  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Application is null : false
2018-11-11 16:41:16.118  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Registered Applications size is zero : true
2018-11-11 16:41:16.118  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Application version is -1: true
2018-11-11 16:41:16.118  INFO 9788 --- [freshExecutor-0] com.netflix.discovery.DiscoveryClient    : Getting all instance registry info from the eureka server
2018-11-11 16:41:18.150 ERROR 9788 --- [tbeatExecutor-0] c.n.d.s.t.d.RedirectingEurekaHttpClient  : Request execution error

com.sun.jersey.api.client.ClientHandlerException: java.net.ConnectException: Connection refused: connect
    at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.filter.GZIPContentEncodingFilter.handle(GZIPContentEncodingFilter.java:123) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.sun.jersey.api.client.Client.handle(Client.java:652) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.WebResource.handle(WebResource.java:682) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.sun.jersey.api.client.WebResource$Builder.put(WebResource.java:529) ~[jersey-client-1.19.1.jar:1.19.1]
    at com.netflix.discovery.shared.transport.jersey.AbstractJerseyEurekaHttpClient.sendHeartBeat(AbstractJerseyEurekaHttpClient.java:102) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$3.execute(EurekaHttpClientDecorator.java:92) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.MetricsCollectingEurekaHttpClient.execute(MetricsCollectingEurekaHttpClient.java:73) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.sendHeartBeat(EurekaHttpClientDecorator.java:89) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$3.execute(EurekaHttpClientDecorator.java:92) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.executeOnNewServer(RedirectingEurekaHttpClient.java:118) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.execute(RedirectingEurekaHttpClient.java:79) ~[eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.sendHeartBeat(EurekaHttpClientDecorator.java:89) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$3.execute(EurekaHttpClientDecorator.java:92) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:120) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.sendHeartBeat(EurekaHttpClientDecorator.java:89) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$3.execute(EurekaHttpClientDecorator.java:92) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.sendHeartBeat(EurekaHttpClientDecorator.java:89) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.DiscoveryClient.renew(DiscoveryClient.java:846) [eureka-client-1.9.3.jar:1.9.3]
    at com.netflix.discovery.DiscoveryClient$HeartbeatThread.run(DiscoveryClient.java:1399) [eureka-client-1.9.3.jar:1.9.3]
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_144]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_144]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_144]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_144]
Caused by: java.net.ConnectException: Connection refused: connect
    at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method) ~[na:1.8.0_144]
    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85) ~[na:1.8.0_144]
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_144]
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_144]
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_144]
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) ~[na:1.8.0_144]
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_144]
    at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_144]
    at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:121) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118) ~[httpclient-4.5.6.jar:4.5.6]
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56) ~[httpclient-4.5.6.jar:4.5.6]
    at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
    ... 27 common frames omitted

原因是Eureka的服务本身分为客户端和服务端，对于注册中心的服务端，其本身也是客户端，其默认的配置有检索服务和自己向自己注册的机制，并且默认是开启的。但是在客户端向服务端注册时，发现服务端本身并没有启动。spring cloud已经默认配置了一套配置，我们不用配置就可以使用。但是其服务注册中心是可以使用的，后期会从源码角度分析其原因

5、工程配置文件

#服务注册中心端口号
server:
  port: 8099

eureka:
  instance:
    #服务注册中心实例的主机名
    hostname: localhost
  client:
    #是否检索服务
    fetch-registry: false
    #是否向服务注册中心注册自己
    register-with-eureka: false
    service-url:
      #服务注册中心的配置内容，指定服务注册中心的位置
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

spring:
  application:
    name: eurka-server

 添加配置文件，修改端口程序名和eureka的相关配置，再次启动程序就可以正常运行了。

到目前为止，其实我们就添加了一个注解和几行配置，程序就可以运行了，极其简单和方便。