{"id":492,"date":"2019-07-13T12:30:47","date_gmt":"2019-07-13T19:30:47","guid":{"rendered":"http:\/\/35.243.195.209\/?p=492"},"modified":"2021-04-19T19:18:47","modified_gmt":"2021-04-20T02:18:47","slug":"dependencymanagement-and-dependencies-in-maven","status":"publish","type":"post","link":"https:\/\/nanzhou.cc\/index.php\/2019\/07\/13\/dependencymanagement-and-dependencies-in-maven\/","title":{"rendered":"DependencyManagement and Dependencies in Maven"},"content":{"rendered":"

Summary<\/h2>\n

In this post, I will introduce the key difference between Maven’s <dependencyManagement><\/code> and <dependencies><\/code>.<\/p>\n

Conclusion<\/h2>\n
    \n
  1. In pom inheritance, artifacts specified <dependencies><\/code> will ALWAYS<\/strong> be included as a dependency of the child module(s). However, artifacts specified in <dependencyManagement><\/code> will only be included if child modules explicitly specify them in <dependencies><\/code>.<\/li>\n
  2. <dependencyManagement><\/code> is good for centralized version control.<\/li>\n
  3. <dependencyManagement><\/code> is good for import managed dependencies from other projects.<\/li>\n<\/ol>\n

    Details<\/h2>\n

    We are always curious to dive deeper and examples are more intuitive than theory. We build a parent pom and a child pom to explain the above conclusions. We install the parent pom into local repo by sudo mvn clean install<\/code>.<\/p>\n

    <!--  Parent pom  -->\n    <groupId>edu.fighternan.java<\/groupId>\n    <artifactId>review<\/artifactId>\n    <version>1.0-SNAPSHOT<\/version>\n    <packaging>pom<\/packaging>\n\n    <dependencies>\n        <dependency>\n            <artifactId>lambda<\/artifactId>\n            <groupId>software.amazon.awssdk<\/groupId>\n        <\/dependency>\n    <\/dependencies>\n\n    <dependencyManagement>\n        <dependencies>\n            <dependency>\n                <groupId>software.amazon.awssdk<\/groupId>\n                <artifactId>bom<\/artifactId>\n                <version>2.3.9<\/version>\n                <type>pom<\/type>\n                <scope>import<\/scope>\n            <\/dependency>\n        <\/dependencies>\n    <\/dependencyManagement>\n\n    <build>\n        <pluginManagement>\n            <plugins>\n                <plugin>\n                    <artifactId>maven-compiler-plugin<\/artifactId>\n                    <version>3.8.0<\/version>\n                    <configuration>\n                        <source>1.8<\/source>\n                        <target>1.8<\/target>\n                    <\/configuration>\n                <\/plugin>\n            <\/plugins>\n        <\/pluginManagement>\n    <\/build><\/code><\/pre>\n
    <!--  Child pom  -->\n    <parent>\n        <groupId>edu.fighternan.java<\/groupId>\n        <artifactId>review<\/artifactId>\n        <version>1.0-SNAPSHOT<\/version>\n    <\/parent>\n\n    <groupId>edu.fighternan.java<\/groupId>\n    <artifactId>review2<\/artifactId>\n    <version>1.0-SNAPSHOT<\/version><\/code><\/pre>\n
    1. Inheritance<\/h3>\n
    The parent pom imports another <dependencyManagement><\/code>, which will be explained later. What we know for now is that the parent pom specifies a dependency explicitly.<\/p>\n
    By execute mvn dependency:tree<\/code>, we can see the denpendency tree.<\/p>\n
    [INFO] edu.fighternan<\/code>.java:review:pom:1.0-SNAPSHOT [INFO] \\- software.amazon.awssdk:lambda:jar:2.3.9:compile<\/code><\/pre>\n
    In the child pom, we do not have any explicit dependencies. However, it has a transitive dependency inherited from its parent.<\/p>\n
    [INFO] edu.fighternan<\/code>.java:review2:jar:1.0-SNAPSHOT [INFO] \\- software.amazon.awssdk:lambda:jar:2.3.9:compile<\/code><\/pre>\n
    If we remove the explicit dependency in parent pom by removing the whole <dependencies><\/code> element. There will be no dependencies for both parent and child anymore.<\/p>\n
    2. Centralized Version Control<\/h3>\n
    In the parent pom, we explicitly declare a AWS lambda<\/code> artifact without version. Actually software.amazon.awssdk.aws-sdk-java-pom<\/code> which is the parent of software.amazon.awssdk.bom<\/code> defines the version. BOM stands for bill of materials<\/code>, which centralizes the version control for any other artifact which imports the BOM.<\/p>\n
    3. Multiple Inheritance<\/h3>\n
    You cannot have a pom-type project as a simple dependency<\/code> in another project. There can only be a parent-child relationship. However, a project can only inherit from a single parent.<\/p>\n
    Import<\/code> scope for pom<\/code> type dependency in <dependencyManagement><\/code> section allows you to achieve the equivalent of multiple inheritances<\/code>. Also, you can leverage the centralized control of <dependencyManagement><\/code>.<\/p>\n
    Reference<\/h2>\n
    Maven’s Official Guide<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
    Summary In this post, I will introduce the key difference between Maven’s <dependencyManagement> and <dependencies>. Conclusion In pom inheritance, artifacts specified <dependencies> will ALWAYS be included as a dependency of the child module(s). However, artifacts specified in <dependencyManagement> will only be included if child modules explicitly specify them in <dependencies>. <dependencyManagement> is good for centralized…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[33,5,25],"tags":[],"class_list":["post-492","post","type-post","status-publish","format-standard","hentry","category-java","category-proglang","category-software-engineering"],"_links":{"self":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/492","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/comments?post=492"}],"version-history":[{"count":5,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/492\/revisions"}],"predecessor-version":[{"id":1581,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/posts\/492\/revisions\/1581"}],"wp:attachment":[{"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/media?parent=492"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/categories?post=492"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/nanzhou.cc\/index.php\/wp-json\/wp\/v2\/tags?post=492"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}