java - Parent pom and microservices

Question

• We have several projects that are microservices, every project is independent (running on separate spring boot server, exposing rest services, using separate DB schema...)
• We use maven to manage the dependencies.

Is it a good idea to have a parent pom declaring each microservices as modules? And so helping to manage the common dependencies (like the lib servlet-api witch is used in every project, to remove it of all of them and declare it in only the parent pom)

Answer 1

The 'problem' with a multi-module parent pom is that, without complicated profiles, it locks the modules in the same release cycle (assuming you're using the Release Plugin, which you should be).

The way I work with Maven is to have a parent pom that declares:

• common dependencies (logging APIs, JUnit, etc).
• common plugins.
• all dependencies in the dependencyManagement section.
• all plugins in the pluginManagement section.

Each module delcares the parent pom as its parent but the parent knows nothing about the modules.

The benefit of this comes from the last to two bullets above, the 'management' sections. Anything contained in a 'management' section needs to be redeclared in a module that wants to use a particular dependency or plugin.

For example the parent might look like this:

<project>

  <groupId>com.example</groupId>
  <artifactId>parent</artifactId>
  <version>1.0.00-SNAPSHOT</version>

  ...

  <dependencies>

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.7.7</version>
    </dependency>

    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>            

  </dependencies>

  <dependencyManagement>

    <dependency>
      <groupId>commons-lang</groupId>
      <artifactId>commons-lang</artifactId>
      <version>2.6</version>
    </dependency>        

    <dependency>
      <groupId>commons-collections</groupId>
      <artifactId>commons-collections</artifactId>
      <version>2.1</version>
    </dependency>

  </dependencyManagement>

  <plugins>

    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.1</version>
      <configuration>
        <source>1.8</source>
        <target>1.8</target>
      </configuration>
    </plugin>

  <plugins>

  <pluginManagement>

    <plugins>

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>2.4</version>
        <configuration>
          <appendAssemblyId>false</appendAssemblyId>
          <descriptors>
            <descriptor>src/main/assembly/assembly.xml</descriptor>
          </descriptors>
        </configuration>
        <executions>
          <execution>
            <id>make-assembly</id>
            <phase>package</phase>
            <goals>
              <goal>single</goal>
            </goals>
          </execution>
        </executions>
      </plugin>

    </plugins>

  </pluginManagement>

</project>

And the module might look like this:

<project>

  <parent>
    <groupId>com.example</groupId>
    <artifactId>parent</artifactId>
    <version>1.0.00-SNAPSHOT</version>
  </parent>

  <groupId>com.example</groupId>
  <artifactId>module</artifactId>
  <version>1.0.00-SNAPSHOT</version>

  <dependencies>

    <dependency>
      <groupId>commons-lang</groupId>
      <artifactId>commons-lang</artifactId>          
    </dependency>        

  </dependencies>

  <plugins>

    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-assembly-plugin</artifactId>
    </plugin>

  </plugins>

</project>

The module would:

• have dependencies on org.slf4j:slf4j-api:1.7.7:compile, junit:junit:4.11:test and commons-lang:commons-lang:2.6:compile.
• has the plugin org.apache.maven.plugins:maven-assembly-plugin:2.4