dependencyManagement

作者: hehehehe | 来源:发表于2020-05-25 11:50 被阅读0次

dependencyManagement 和 dependencies 区别

dependencyManagement：

只是声明依赖，并不实现引入，因此子项目需要显示的声明需要用的依赖。如果不在子项目中声明依赖，是不会从父项目中继承下来的；只有在子项目中写了该依赖项，并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，那么会使用子项目中指定的jar版本

dependencies：

相对于dependencyManagement，所有生命在dependencies里的依赖都会自动引入，并默认被所有的子项目继承。
原来dependencyManagement 只是申明依赖，并不实现引入。问题就在这里了，把依赖放到dependencies里面

1.在同一个pom文件下，如果<dependencies>和<dependencyManagement>中都对该jar做了依赖，以<dependencies>的为准，优先级高于<dependencyManagement>。若前者没有对其依赖，而后者对其有依赖，则以后者为准。<dependencyManagement>里只是声明依赖，并不实现引入.

2.在不同的pom文件中，存在父子相互依赖关系的，父项目的pom中<dependencyManagement>中对该jar做了依赖，而子项目中<dependencies>又依赖了该jar，如果子项目中没有指定<version>和<scope>，则继承父项目中该jar的<version>和<scope>。如果子项目中指定了<version>和<scope>，以子项目的为准。

引入SpringBoot的两种方法

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <!-- Import dependency management from Spring Boot -->
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.0.4.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

demo0

简单分析一下，最外层是pf-login，下面有client、server、dao三个模块：
①、client模块用于注册服务，提供服务的调用接口，是调用login服务的入口。
②、server模块用于处理业务逻辑。
③、dao模块用于数据持久，和数据库打交道。
我们还可以加一些其他的模块，比如common,base之类的用来存放公共工具等等。
模块间的依赖关系：client 依赖 server ，server 依赖 dao。

1、pf-login的pom.xml（最外层，也是父目录）

<?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>cn.pw</groupId>
    <artifactId>pf-login</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>
    <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>Dalston.SR4</spring-cloud.version>
        <fastjson-version>1.2.15</fastjson-version>
    </properties>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.8.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>${fastjson-version}</version>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <modules>
        <module>pf-login-client</module>
        <module>pf-login-dao</module>
        <module>pf-login-server</module>
    </modules>
</project>

所有关于pf-login模块的依赖都统一写在了这里，为了方便管理和避免重复依赖。与之前略有不同的是，我们加入了数据库的依赖组件，jpa和mysql。
我们也注意到了pom中引入了阿里巴巴的fastjson，这个与其他依赖写法不同，也就证明SpringBoot是支持第三方依赖，也支持自定义依赖的。
<modules>是多模块项目的关键，模块简的关系正是通过父pom添加<modules>，子pom添加<parent>来建立的。

2、pf-login-client的pom.xml

<?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>
    <parent>
        <groupId>cn.pw</groupId>
        <artifactId>pf-login</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>
 
    <artifactId>pf-login-client</artifactId>
    <name>pf-login-client</name>
    <dependencies>
        <dependency>
            <groupId>cn.pw</groupId>
            <artifactId>pf-login-server</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

上面我们设计了client 依赖 server，所以pom中添加了对 server的dependency。

3、pf-login-server的pom.xml

<?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>
    <parent>
        <groupId>cn.pw</groupId>
        <artifactId>pf-login</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>
 
    <artifactId>pf-login-server</artifactId>
    <dependencies>
        <dependency>
            <groupId>cn.pw</groupId>
            <artifactId>pf-login-dao</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>
</project>

4、pf-login-dao的pom.xml

<?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>
    <parent>
        <groupId>cn.pw</groupId>
        <artifactId>pf-login</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>
 
    <artifactId>pf-login-dao</artifactId>
</project>

demo1

parent

<?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.demo</groupId>
    <artifactId>demo-parent</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>pom</packaging>

    <name>demo-parent</name>
    <description>Demo project for Spring Boot</description>

    <!-- 删除 -->
    <!--<parent>-->
        <!--<groupId>org.springframework.boot</groupId>-->
        <!--<artifactId>spring-boot-starter-parent</artifactId>-->
        <!--<version>2.0.5.RELEASE</version>-->
        <!--<relativePath/> &lt;!&ndash; lookup parent from repository &ndash;&gt;-->
    <!--</parent>-->

    <modules>
        <module>demo-apply</module>
        <module>demo-common</module>
        <module>demo-static</module>
    </modules>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

<!--
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter</artifactId>
                <version>2.0.5.RELEASE</version>
            </dependency>

            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
                <version>2.0.5.RELEASE</version>
            </dependency>

            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <version>2.0.5.RELEASE</version>
                <scope>test</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
-->

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-dependencies</artifactId>
            <version>1.5.1.RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>${java.version}</source>
                    <target>${java.version}</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

children

<?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>

    <artifactId>demo-apply</artifactId>
    <packaging>jar</packaging>

    <name>demo-apply</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>com.demo</groupId>
        <artifactId>demo-parent</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <relativePath>../pom.xml</relativePath><!-- lookup parent from repository -->
    </parent>

    <dependencies>
        <!-- 加入其余模块的依赖 -->
        <dependency>
            <groupId>com.demo</groupId>
            <artifactId>demo-common</artifactId>
            <version>0.0.1-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>com.demo</groupId>
            <artifactId>demo-static</artifactId>
            <version>0.0.1-SNAPSHOT</version>
            <type>war</type>
        </dependency>

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

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

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <!-- 当所依赖的其他模块，有启动类的时候，需要以下配置，指定唯一启动类，
                        本次事例未涉及其他模块有启动类，可自行测试 -->
                <configuration>
                    <!-- 指定该Main Class为全局的唯一入口 -->
                    <mainClass>com.demo.demoapply.DemoApplyApplication</mainClass>
                    <layout>ZIP</layout>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal><!--可以把依赖的包都打包到生成的Jar包中-->
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

demo2

当我们的项目模块很多的时候，我们使用Maven管理项目非常方便，帮助我们管理构建、文档、报告、依赖、scms、发布、分发的方法。可以方便的编译代码、进行依赖管理、管理二进制库等等。
由于我们的模块很多，所以我们又抽象了一层，如下图抽出一个femicro来管理子项目的公共的依赖。为了项目的正确运行，必须让所有的子项目使用依赖项的统一版本，必须确保应用的各个项目的依赖项和版本一致，才能保证测试的和发布的是相同的结果。
在我们项目顶层的POM文件中，我们会看到dependencyManagement元素。通过它元素来管理jar包的版本，让子项目中引用一个依赖而不用显示的列出版本号。Maven会沿着父子层次向上走，直到找到一个拥有dependencyManagement元素的项目，然后它就会使用在这个dependencyManagement元素中指定的版本号。

本项目中，父类 femicro pom中dependencyManagement配置

    <!--依赖管理，用于管理spring-cloud的依赖-->
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.M8</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>fastjson</artifactId>
                <version>1.2.33</version>
            </dependency>
            <dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>druid</artifactId>
                <version>1.0.11</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

<?xml version="1.0"?>
<project
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
    xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>io.fredia</groupId>
        <artifactId>femicro</artifactId>
        <version>1.0.0-SNAPSHOT</version>
    </parent>
    <artifactId>femicro-cache</artifactId>
    <name>femicro-cache</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
        </dependency>
        <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/log4j-over-slf4j -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>log4j-over-slf4j</artifactId>
            <version>1.7.7</version>
        </dependency>
    </dependencies>
</project>

dependencyManagement