最近想把項目中的一個功能設(shè)計成一個microservice，降低系統(tǒng)件的耦合度痒谴，方便后期維護(hù)與擴(kuò)展魏蔗。之前沒有接觸過microservice舰绘，只是知道m(xù)icroservice最近兩年比較火虱而。作為技術(shù)人員總喜歡折騰新技術(shù)筏餐，所以決定上網(wǎng)找個quick starter，結(jié)果找到了這篇https://spring.io/blog/2015/07/14/microservices-with-spring牡拇。

按照文中的步驟魁瞪，首先需要創(chuàng)建一個服務(wù)注冊（service registration）項目穆律。文中給出的guide很簡潔，自己新建了一個spring boot project佩番，copy了提供的POM配置众旗，結(jié)果運行時卻碰到了如下錯誤：

java.lang.NoSuchMethodError: org.springframework.boot.builder.SpringApplicationBuilder.<init>([Ljava/lang/Object;)V
    at org.springframework.cloud.bootstrap.BootstrapApplicationListener.bootstrapServiceContext(BootstrapApplicationListener.java:161)
    at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:102)
    at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:68)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)
    at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:74)
    at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:54)
    at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:358)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:317)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243)
    at demo.ms.robossliu.demo.DemoApplication.main(DemoApplication.java:14)

尤其是第一行信息，似乎提示一個莫名其妙的無此方法錯誤趟畏。Spring boot框架很多組件都是基于依賴注入（DI），有些錯誤在編譯時可能無法被檢測出來滩租，只有在運行時才暴露出來赋秀。既然提示無此方法，那么肯定是某個組件（包）有問題：要么未被注入律想；要么版本版本不對猎莲。

也沒有過多考慮，直接bing一下（雖然想用google技即，但確實慢）著洼，看了幾篇stackoverflow上的文章，基本可以斷定是依賴包之間存在的兼容性問題而叼，導(dǎo)致bean未能正確被注入身笤。自己檢查了這份copy出來的POM文件：

<parent>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-parent</artifactId>
       <version>2.0.0.RELEASE</version>
   </parent>

   <dependencies>
       <dependency>
           <!-- Setup Spring Boot -->
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter</artifactId>
       </dependency>

       <dependency>
           <!-- Setup Spring MVC & REST, use Embedded Tomcat -->
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-web</artifactId>
       </dependency>

       <dependency>
           <!-- Spring Cloud starter -->
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-starter</artifactId>
       </dependency>

       <dependency>
           <!-- Eureka for service registration -->
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-starter-eureka-server</artifactId>
       </dependency>
   </dependencies>

  <!-- Spring Cloud dependencies -->
   <dependencyManagement>
       <dependencies>
           <dependency>
               <groupId>org.springframework.cloud</groupId>
               <artifactId>spring-cloud-dependencies</artifactId>
               <version>Edgware.SR3</version>
               <type>pom</type>
               <scope>import</scope>
           </dependency>
       </dependencies>
   </dependencyManagement>

發(fā)現(xiàn)自己使用的是spring boot 2.0.0版本，spring cloud使用是Edgware.SR3版本葵陵，難道是兩者沖突液荸？對于Edgware.SR3是哪個版本的spring cloud以及依賴的spring boot版本，自己不是很清楚脱篙，畢竟之前沒有玩過娇钱。打開了spring cloud官網(wǎng)，發(fā)現(xiàn)Edgware.SR3版本依賴于spring boot 1.5.x绊困。如此看來是這兩個組件的版本發(fā)生了沖突文搂，所以解決方法也比較簡單：要么降級spring boot版本，要么升級spring cloud版本秤朗。內(nèi)心一直秉持著一種理念“新技術(shù)總是更好”煤蹭，于是果斷選擇升級spring cloud至最新版本Finchley。修改POM文件之后川梅，編譯運行一切OK了疯兼。

修改之后的POM文件如下，供大家參考一下：

<?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>demo.ms.robossliu</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath/>
    </parent>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <version>2.0.0.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka-server</artifactId>
            <version>1.4.4.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
            <version>1.4.4.RELEASE</version>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.BUILD-SNAPSHOT</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <repositories>
        <repository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/libs-snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
    </repositories>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>