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Maven Things

Missing pom.xml version

If version in pom.xml isnt mentioned, then how does spring boot know which version to use ?

The version belonging the parent module will be referenced. Spring Boot starter comes with a lot of libraries in-built, with is referenced as a parent in the pom.xml file of your project 

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
  • Click on spring-boot-starter-parent and to open its' pom.xml and then open spring-boot-dependencies and you will find the list of version of each dependencies mentioned in it, used the specific spring-boot version you are using.

Now, if we have a child module in our spring application, and if we dont specify the version number, we either need to mention the parent pom or specify the version there.

<!-- referencing parent pom.xml -->
        <parent>
        <groupId>com.example</groupId>
        <artifactId>spring-demo</artifactId>
        <version>0.0.1</version>
        <relativePath>../pom.xml</relativePath>
    </parent>

or you can the specify the version inside the dependency tag or in the properties tag

    <properties>
        <java.version>17</java.version>
        <lombok.version>1.18.18</lombok.version> <!-- example -->
    </properties>

You can also exclude the child module ( if you want to use another implementation ) from the parent pom.

Example : Excluding the artifactedId hamcrest-core from junit.

<dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
                <scope>test</scope>
                <exclusions>
                    <exclusion>
                        <groupId>org.hamcrest</groupId>
                        <artifactId>hamcrest-core</artifactId>
                    </exclusion>
                </exclusions>
            </dependency>
        </dependencies>
    </dependencyManagement>
  • Check the maven tab, you will find that hamcrest-core is no longer a sub-dependency of junit and will also find the exact version.

Maven Build Phases

  • validate - validate the project is correct and all necessary information is available
  • compile - compile the source code of the project
  • test - test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed
  • package - take the compiled code and package it in its distributed format, such as a JAR.
  • verify - run any checks on results of integration tests to ensure quality criteria are met
  • install - install the package into the local repository, for use as a dependency in other projects locally
  • deploy - done in the build environment, copies the final package to the remote repository for sharing with other developers and projects.