Maven依赖管理

  1. 依赖管理

依赖管理,可以将有关依赖项的所有信息放在共同的POM中,并对子POM中的工件进行更简单的引用。举个例子:

父POM

<project>
    ......
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>group-a</groupId>
                <artifactId>artifact-a</artifactId>
                <version>1.0</version>
                <exclusions>
                    <exclusion>
                        <groupId>group-c</groupId>
                        <artifactId>excluded-artifact</artifactId>
                    </exclusion>
                </exclusions>
            </dependency>
            <dependency>
                <groupId>group-c</groupId>
                <artifactId>artifact-b</artifactId>
                <version>1.0</version>
                <type>war</type>
                <scope>runtime</scope>
            </dependency>
            <dependency>
                <groupId>group-a</groupId>
                <artifactId>artifact-b</artifactId>
                <version>1.0</version>
                <type>bar</type>
                <scope>runtime</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    ......
</project>

两个子POM

<project>
    ...
    <dependencies>
        <dependency>
            <groupId>group-a</groupId>
            <artifactId>artifact-a</artifactId>
        </dependency>

        <dependency>
            <groupId>group-a</groupId>
            <artifactId>artifact-b</artifactId>
            <!-- This is not a jar dependency, so we must specify type. -->
            <type>bar</type>
        </dependency>
    </dependencies>
</project>


<project>
    ...
    <dependencies>
        <dependency>
            <groupId>group-c</groupId>
            <artifactId>artifact-b</artifactId>
            <!-- This is not a jar dependency, so we must specify type. -->
            <type>war</type>
        </dependency>

        <dependency>
            <groupId>group-a</groupId>
            <artifactId>artifact-b</artifactId>
            <!-- This is not a jar dependency, so we must specify type. -->
            <type>bar</type>
        </dependency>
    </dependencies>
</project>

在<dependencyManagement>区域,实际上是根据**{groupId, artifactId, type, classifier}** 来进行依赖匹配的。自从<type>字段的默认值是jar以后,最简单的标识只需要设置**{groupId, artifactId}**即可。

依赖管理的另一个重要的作用是统一管理(控制)依赖的版本。这一点不再赘述。

  1. 导入依赖

依赖可以继承,但是目前只支持单继承,可以通过"import"的方式从其它POM中导入依赖。

下面的例子,Z导入了X和Y管理的依赖。

<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>maven</groupId>
    <artifactId>Z</artifactId>
    <packaging>pom</packaging>
    <version>1.0</version>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>maven</groupId>
                <artifactId>X</artifactId>
                <version>1.0</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>maven</groupId>
                <artifactId>Y</artifactId>
                <version>1.0</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

举个例子

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.example</groupId>
        <artifactId>demo-parent</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo001</artifactId>
    <version>0.0.1-SNAPSHOT</version>

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

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.7.11</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>
  1. 版本管理插件

https://www.mojohaus.org/versions/versions-maven-plugin/index.html

versions插件用于管理、模块、依赖和插件的版。该插件有很多目标,为了统一管理父子项目版本号,我们这里只用其中三个。

操作很简单,首先,在父工程中引入versions插件

<!-- 父POM中增加插件 -->
<build>
    <plugins>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>versions-maven-plugin</artifactId>
            <version>2.16.2</version>
            <configuration>
                <generateBackupPoms>false</generateBackupPoms>
            </configuration>
        </plugin>
    </plugins>
</build>

然后,更新父工程的版本号

mvn versions:set -DnewVersion="2.0.0-SNAPSHOT" //更新整个项目版本

接着,把子模块的版本更新成父工程的版本号

mvn versions:update-child-modules

最后提交

mvn versions:commit
  1. BOM

对于一个项目来说,使用"库"中的一个或多个构件是相当常见的。为了使项目中使用的构件的版本与库中分发的版本保持同步。我们可以创建一个"物料清单"(BOM)以供其它项目使用。

简单的来讲,就是多个项目都需要依赖某些包时,为了方便管理版本,使得多个项目中引用的某个包的版本保持一致,这个时候我们就定义一个"库",在这个库中统一定义包的版本,使用的时候只需要导入这个库即可。

举个例子:

定义一个库(其实就是一个POM)

<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.test</groupId>
    <artifactId>mytest-bom</artifactId>
    <version>1.0.0</version>
    <packaging>pom</packaging>
    <properties>
        <project1Version>1.0.0</project1Version>
        <project2Version>1.0.0</project2Version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.test</groupId>
                <artifactId>project1</artifactId>
                <version>${project1Version}</version>
            </dependency>
            <dependency>
                <groupId>com.test</groupId>
                <artifactId>project2</artifactId>
                <version>${project2Version}</version>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

然后,定义两个项目project1和project2

<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>
    <parent>
        <groupId>com.test</groupId>
        <artifactId>mytest-bom</artifactId>
        <version>1.0.0</version>
    </parent>

    <groupId>com.test</groupId>
    <artifactId>parent</artifactId>
    <version>1.0.0</version>
    <packaging>pom</packaging>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.apache.logging.log4j</groupId>
                <artifactId>log4j-core</artifactId>
                <version>2.22.0</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

</project>

project1

<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>
    <parent>
        <groupId>com.test</groupId>
        <artifactId>parent</artifactId>
        <version>1.0.0</version>
    </parent>
    <groupId>com.test</groupId>
    <artifactId>project1</artifactId>
    <version>${project1Version}</version>
    <packaging>jar</packaging>

    <dependencies>
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
        </dependency>
    </dependencies>
</project>

project2

<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>
    <parent>
        <groupId>com.test</groupId>
        <artifactId>parent</artifactId>
        <version>1.0.0</version>
    </parent>
    <groupId>com.test</groupId>
    <artifactId>project2</artifactId>
    <version>${project2Version}</version>
    <packaging>jar</packaging>
</project>

最后,在其它项目中引用project1和project2

<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.test</groupId>
	<artifactId>use</artifactId>
	<version>1.0.0</version>
	<packaging>jar</packaging>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>com.test</groupId>
				<artifactId>mytest-bom</artifactId>
				<version>1.0.0</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>com.test</groupId>
			<artifactId>project1</artifactId>
		</dependency>
		<dependency>
			<groupId>com.test</groupId>
			<artifactId>project2</artifactId>
		</dependency>
	</dependencies>
</project>

可以看到,使用的时候,直接导入这个POM,然后按需引用

核心就是在一个公共的pom中定义包的版本和依赖管理,然后在使用的时候导入公共pom

假设现在在做一个项目,其中有两个子项目,在cjs-store-service中需要引用cjs-workflow-provider-api

先定义一个公共的pom

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>cjs-dependencies-bom</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <properties>
        <store.version>0.0.4-SNAPSHOT</store.version>
        <workflow.version>0.0.3-SNAPSHOT</workflow.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.example</groupId>
                <artifactId>cjs-store-provider-api</artifactId>
                <version>${store.version}</version>
            </dependency>
            <dependency>
                <groupId>com.example</groupId>
                <artifactId>cjs-workflow-provider-api</artifactId>
                <version>${workflow.version}</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

</project>

项目中引用

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>com.example</groupId>
        <artifactId>cjs-store</artifactId>
        <version>0.0.4-SNATHOST</version>
    </parent>
    <groupId>com.example</groupId>
    <artifactId>cjs-store-service</artifactId>
    <version>0.0.4-SNATHOST</version>
    
    <dependencies>
        <dependency>
            <groupId>com.example</groupId>
            <artifactId>cjs-store-dto</artifactId>
            <version>${project.parent.version}</version>
        </dependency>
        <dependency>
            <groupId>com.example</groupId>
            <artifactId>cjs-workflow-provider-api</artifactId>
        </dependency>
    </dependencies>

    <!-- 如果父工程cjs-store的parent不是cjs-dependencies-bom,则这里需要import,否则不需要,因为可以直接通过继承得到 -->
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.example</groupId>
                <artifactId>cjs-dependencies-bom</artifactId>
                <version>1.0.0-SNAPSHOT</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
</project>

其实,这种依赖包管理可以学习一下dubbo

  1. 项目启动问题

如果你的springboot项目起不来,控制台也不打印任何报错信息,就像这样

那么,你可以在SpringApplication.run()这一行打断点

然后,就可以看到报错了

  1. 演示

Maven -- Settings Reference (apache.org)

Maven -- Guide to Mirror Settings (apache.org)

Maven -- POM Reference (apache.org)

Maven -- Best Practice - Using a Repository Manager (apache.org)