Page Comparison

The only real reason I authored this page was to say that where possible, it will be best to store all of the version numbers of the various jars your project depends on in your base pom. Properties look like this:

<project>
  <groupId>acme.com</groupId>
  <artifactId>acme-pom</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  ...
  <properties>
    <propertyname>propertyvalue</propertyname>
    <spring-portlet.version>2.0.3</spring-portlet.version>
    <portlet-api.version>1.0</portlet-api.version>
  </properties>
  ...
</project>

Properties are arbitrary key/value pairs. They can store anything, including version numbers. They are interpolated (ie. variable substitution is performed).

You can use a property anywhere in your pom.xml file, or in filtered resources (again the Maven docs will tell it better than I), or in aggregated (sub-project) pom.xml files.

When you enclose a property name with a dollar-sign and curly braces - ${propertyname} - it will be substituted with the actual value. Below the <version> used for the Spring Portlet MVC jar will be the value of the property spring-portlet.version which - as defined above - is 2.0.3. When you want to upgrade Spring, just change the value of the property and re-compile.

<project>
  <parent>
    <groupId>acme.com</groupId>
    <artifactId>acme-pom</artifactId>
    <version>1.0-SNAPSHOT</version>
  </parent>
  <groupId>acme.com</groupId>
  <artifactId>acme-portlet</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>
  ...
  <dependencies>
    <dependency>
      <groupId>org.springframwork</groupId>
      <artifactId>spring-portlet</artifactId>
      <version>${spring-portlet.version}</version>
    </dependency>
  </dependencies>
</project>

The point being that the property spring-portlet.version is defined in the base pom, and its value can be interpolated in sub-project poms.