Why does resolved dependencies differ between Java 8 and Java 11?

Question

Given a very simple Maven project with a single pom-file containing a single dependency:

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.example</groupId>
  <artifactId>maven-test</artifactId>
  <version>1.0-SNAPSHOT</version>

  <dependencies>
    <dependency>
      <groupId>org.apache.cxf.xjc-utils</groupId>
      <artifactId>cxf-xjc-runtime</artifactId>
      <version>3.3.0</version>
    </dependency>
  </dependencies>

</project>

When running mvn dependency:tree different results are given depending on Java version.

With Java 8:

[INFO] Scanning for projects...
[INFO] 
[INFO] -----------------------< org.example:maven-test >-----------------------
[INFO] Building maven-test 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ maven-test ---
[INFO] org.example:maven-test:jar:1.0-SNAPSHOT
[INFO] \- org.apache.cxf.xjc-utils:cxf-xjc-runtime:jar:3.3.0:compile
[INFO]    \- jakarta.xml.bind:jakarta.xml.bind-api:jar:2.3.2:compile
[INFO]       \- jakarta.activation:jakarta.activation-api:jar:1.2.1:compile
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  0.982 s
[INFO] Finished at: 2020-06-22T15:05:56+02:00
[INFO] ------------------------------------------------------------------------

With Java 11:

[INFO] Scanning for projects...
[INFO] 
[INFO] -----------------------< org.example:maven-test >-----------------------
[INFO] Building maven-test 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ maven-test ---
[INFO] org.example:maven-test:jar:1.0-SNAPSHOT
[INFO] \- org.apache.cxf.xjc-utils:cxf-xjc-runtime:jar:3.3.0:compile
[INFO]    +- jakarta.xml.bind:jakarta.xml.bind-api:jar:2.3.2:compile
[INFO]    |  \- jakarta.activation:jakarta.activation-api:jar:1.2.1:compile
[INFO]    +- javax.annotation:javax.annotation-api:jar:1.3.1:compile           <-- This and below only with Java 11
[INFO]    +- javax.xml.ws:jaxws-api:jar:2.3.0:compile
[INFO]    |  +- javax.xml.bind:jaxb-api:jar:2.3.0:compile
[INFO]    |  \- javax.xml.soap:javax.xml.soap-api:jar:1.4.0:compile
[INFO]    \- javax.activation:activation:jar:1.1.1:compile
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  1.261 s
[INFO] Finished at: 2020-06-22T15:05:51+02:00
[INFO] ------------------------------------------------------------------------

I would have expected the trees to be the same under the two Java versions.

Maven version is 3.6.0.

Why do the resolved dependencies differ between the Java versions?

Answer 1

The reason why the dependency tree differs between the Java versions is found in the dependency:

<dependency>
  <groupId>org.apache.cxf.xjc-utils</groupId>
  <artifactId>cxf-xjc-runtime</artifactId>
  <version>3.3.0</version>
</dependency>

This in turn has xjc-utils as its parent:

<parent>
    <groupId>org.apache.cxf.xjc-utils</groupId>
    <artifactId>xjc-utils</artifactId>
    <version>3.3.0</version>
</parent>

In this POM file, we find the dependencies that are excluded when building with Java 8:

<profile>
    <id>java9-plus</id>
    <activation>
        <jdk>[9,)</jdk>
    </activation>
    <dependencies>
        <dependency>
            <groupId>javax.annotation</groupId>
            <artifactId>javax.annotation-api</artifactId>
            <version>1.3.1</version>
        </dependency>
        <dependency>
            <groupId>javax.xml.ws</groupId>
            <artifactId>jaxws-api</artifactId>
            <version>2.3.0</version>
        </dependency>
        <dependency>
            <groupId>javax.activation</groupId>
            <artifactId>activation</artifactId>
            <version>1.1.1</version>
        </dependency>
    </dependencies>
 </profile>

This pretty much speacks for itself, the dependencies will only be included if Java 9 or above is used, as stated in this range: <jdk>[9,)</jdk>. The documentation for the tag states:

Specifies that this profile will be activated when a matching JDK is detected. For example, 1.4 only activates on JDKs versioned 1.4, while !1.4 matches any JDK that is not version 1.4.

This activation profile makes sure these dependencies are included when Java 11 is used:

[INFO]    +- javax.annotation:javax.annotation-api:jar:1.3.1:compile
[INFO]    +- javax.xml.ws:jaxws-api:jar:2.3.0:compile
[INFO]    |  +- javax.xml.bind:jaxb-api:jar:2.3.0:compile
[INFO]    |  \- javax.xml.soap:javax.xml.soap-api:jar:1.4.0:compile
[INFO]    \- javax.activation:activation:jar:1.1.1:compile

---

More info about activation can be found in the official Maven documentation:

Activations are the key of a profile. The power of a profile comes from its ability to modify the basic POM only under certain circumstances. Those circumstances are specified via an activation element.

Together with another example of activation based on Java version:

<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">
  ...
  <profiles>
    <profile>
      <id>test</id>
      <activation>
        <activeByDefault>false</activeByDefault>
        <jdk>1.5</jdk>
        <os>
          <name>Windows XP</name>
          <family>Windows</family>
          <arch>x86</arch>
          <version>5.1.2600</version>
        </os>
        <property>
          <name>sparrow-type</name>
          <value>African</value>
        </property>
        <file>
          <exists>${basedir}/file2.properties</exists>
          <missing>${basedir}/file1.properties</missing>
        </file>
      </activation>
      ...
    </profile>
  </profiles>
</project>

Answer 2

Dependency tree mojo trims lower level dependencies if the dependency is already present higher in the tree.

We can use verbose flag (-Dverbose) to show the excluded dependencies.

To find a specific artifact : mvn dependency:tree -Dverbose -Dincludes=[groupId]:[artifactId]:[type]:[version]

Please visit Maven Dependency Tree to know more.