一、作用

使用dependencyManagement可以统一管理项目中依赖包的版本号，当需要变更版本号时只需在父pom中修改即可；如果某个子项目需要指定一个特殊的版本号时，只需要在自己项目的pom.xml中显示声明一个版本号即可，此时子项目会使用自己声明的版本号，而不继承父项目的版本号

二、dependencyManagement与dependencies的区别

• dependencies相对于dependencyManagement，所有声明在dependencies里的依赖都会自动引入，并默认被所有的子项目继承
• dependencyManagement里只是声明依赖，并不会自动引入，因此子项目需要显示声明依赖。在子项目中声明了依赖项，且没有指定具体版本，才会从父项目中继承该项，并且version和scope都读取自父pom；另外如果子项目中指定了版本号，则会使用子项目中指定的版本

⚠️注意：一个无子工程的独立工程中如果使用dependencyManagement，那么它自己的pom.xml文件引入的依赖也可以不指定版本

<?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.ume.qa</groupId>
    <artifactId>SpringCloudGateway</artifactId>
    <version>1.0-SNAPSHOT</version>

    <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>3.0.1</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
        	<groupId>org.springframework.boot</groupId>
        	<artifactId>spring-boot-starter-actuator</artifactId>
    	</dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-gateway</artifactId>
            <version>3.0.3</version>
        </dependency>
        <!--  SpringCloud alibaba nacos    -->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
            <exclusions>
                <exclusion>
                    <artifactId>spring-cloud-context</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
                <exclusion>
                    <artifactId>spring-cloud-commons</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
                <exclusion>
                    <artifactId>spring-cloud-starter</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-bootstrap</artifactId>
        </dependency>

        <!--fegin组件-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
            <version>3.0.2</version>
            <exclusions>
                <exclusion>
                    <artifactId>spring-cloud-commons</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
                <exclusion>
                    <artifactId>spring-cloud-starter</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
            </exclusions>
        </dependency>
        <!-- Feign Client for loadBalancing -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-loadbalancer</artifactId>
            <version>3.0.2</version>
            <exclusions>
                <exclusion>
                    <artifactId>spring-cloud-commons</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
                <exclusion>
                    <artifactId>spring-cloud-context</artifactId>
                    <groupId>org.springframework.cloud</groupId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.4.2</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>2.2.5.RELEASE</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>