spring/spring boot 如何解决spring 多版

先看一段官方的说明。
  It is possible to accidentally(意外地) mix different versions of Spring JARs when using Maven. For example, you may find that a third-party(第三方) library, or another Spring project, pulls in atransitive dependency(传递依赖) to an older release. If you forget to explicitly(明确地) declare(声明) a direct(直接) dependency yourself, all sorts of unexpected issues can arise(可能出现各种意想不到的问题).

To overcome(克服) such problems Maven supports the concept of a "bill of materials" (BOM) dependency. You can import the spring-framework-bom in yourdependencyManagement section to ensure(确保) that all spring dependencies (both direct and transitive) are at the same version.

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-framework-bom</artifactId>
            <version>4.2.5.RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

An added benefit of using the BOM(使用BOM的附加好处) is that youno longer need(不再需要) to specify(详细说明) the <version> attribute(属性) when depending on Spring Framework artifacts:

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
    </dependency>
<dependencies

通俗的讲，为了防止用Maven管理Spring项目时，不同的项目依赖了不同版本的Spring，可以使用Maven BOM来解决者一问题。
在依赖管理时，引入spring-framework-bom，即可统一版本，而且，在引入BOM之后，在引入其他Spring依赖时，都无需指定版本。
springboot 使用spring-boot-dependencies、platform-bom来进行配置。

</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>1.5.5.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>
<dependency>
<groupId>io.spring.platform</groupId>
<artifactId>platform-bom</artifactId>
<version>2.0.1.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>