Using Settings.xml to handle Multiple Mirrors in Maven

The goal of having an internal artifactory is to host library for maven, so everytime we do java build, we dont need to pull the whole libraries from internet. Usally we have something like Nexus or JFrog for this.

But the thing is, sometimes we already have a working application that is running well when pulling libraries from online before, and now we need to change it into pointing into our artifact repository without have to change the maven’s pom.xml configuration.

for example, we have some pom.xml file which is pointing to a specific online repository like the sample below,

<?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>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.7.4</version>
		<relativePath /> 
	</parent>
	<groupId>com.something</groupId>
	<artifactId>some-java-app</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>some-java-app</name>
	<description>some java app</description>
	<properties>
		<java.version>17</java.version>
		<tomcat.version>9.0.68</tomcat.version>
	</properties>
	<repositories>
		<repository>
			<id>splunk-releases</id>
			<name>Splunk Releases</name>
			<url>https://splunk.jfrog.io/splunk/ext-releases-local</url>
		</repository>
		<repository>
			<id>spring-releases</id>
			<name>Spring Releases</name>
			<url>https://repo.spring.io/libs-release</url>
		</repository>
	</repositories>
	...
</project>

We can see that application is connecting to multiple maven repositories, such as Splunk JFrog and Spring Repository, other than the default Maven Central.

For this approach, we can create a custom settings.xml and implement a multiple mirror approach for handling to this problem. The result is looks like below xml,

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
    <servers>
        <server>
            <id>default</id>
            <username>username</username>
            <password>password</password>
        </server>
        <server>
            <id>splunk-releases</id>
            <username>username</username>
            <password>password</password>
        </server>
		<server>
            <id>spring-releases</id>
            <username>username</username>
            <password>password</password>
        </server>
    </servers>

    <mirrors>
        <mirror>
            <id>default</id>
            <name>Default Repository</name>
            <url>https://my-artifact-repository/default/maven2/</url>
            <mirrorOf>*, !splunk-releases, !spring-releases</mirrorOf>
        </mirror>
        <mirror>
            <id>splunk-releases</id>
            <name>Splunk Local Repository</name>
            <url>https://my-artifact-repository/splunk/maven2/</url>
            <mirrorOf>splunk-releases</mirrorOf>
        </mirror>
		<mirror>
            <id>spring-releases</id>
            <name>Spring Local Repository</name>
            <url>https://my-artifact-repository/spring/maven2/</url>
            <mirrorOf>spring-releases</mirrorOf>
        </mirror>
    </mirrors>
</settings>

As we can see on above, we have multiple mirror of repositories with each pointing to different local artifact repository endpoints. We can run maven build with having this configuration as parameter.

$ mvn clean package -s settings.xml