maven bom的作用

作为Java 开发我们经常会遇到

java.lang.NoSuchMethodError
java.lang.ClassNotFoundException

自己定义的一堆依赖会出现版本冲突，导致有些方法、类版本不对。

通常公司会有一个团队专门维护一些通用的依赖版本，将这些版本信息固定到一个pom文件里，后期bom的维护方负责版本升级，确保各个依赖之间没有版本冲突。
本质上bom还是一个普通的pom文件，BOM是（Bill of Materials Dependency）依赖列表。
一个bom例子如下

<?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>com.ydj.qd</groupId>
    <artifactId>inf-bom</artifactId>
    <version>1.0</version>
    <packaging>pom</packaging>

    <name>inf-bom</name>
    <description>第三方jar包统一管理</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring.version>4.3.15.RELEASE</spring.version>
    </properties>
    <dependencyManagement>
        <dependencies>

            <!-- 阿里 -->
            <!-- https://mvnrepository.com/artifact/com.alibaba/druid -->
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid</artifactId>
                <version>1.1.12</version>
            </dependency>
            <!-- https://mvnrepository.com/artifact/com.aliyun.mns/aliyun-sdk-mns -->
            <dependency>
                <groupId>com.aliyun.mns</groupId>
                <artifactId>aliyun-sdk-mns</artifactId>
                <version>1.1.8</version>
                <classifier>jar-with-dependencies</classifier>
            </dependency>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>fastjson</artifactId>
                <version>1.2.29</version>
            </dependency>

            <!-- Apache -->
            <dependency>
                <groupId>org.apache.commons</groupId>
                <artifactId>commons-lang3</artifactId>
                <version>3.3.2</version>
            </dependency>
            <dependency>
                <groupId>commons-collections</groupId>
                <artifactId>commons-collections</artifactId>
                <version>3.2.2</version>
            </dependency>
            <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
            <dependency>
                <groupId>com.google.guava</groupId>
                <artifactId>guava</artifactId>
                <version>27.0.1-jre</version>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

业务方使用姿势

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.ydj.qd</groupId>
            <artifactId>inf-bom</artifactId>
            <version>1.0</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
        </dependency>
    </dependencies>
</dependencyManagement>

用户只需要在dependencyManagement声明对bom的依赖，然后就可以在实际使用的地方去掉version字段就可以了, 如果需要使用不同于bom中的版本直接使用<version>覆盖即可