Maven cannot resolve dependency for module in same multi-module project

74
votes

When running commands such as 

mvn dependency:build-classpath

or

mvn exec:java

Maven is unable to resolve a dependency of one of my modules on another.

[ERROR] Failed to execute goal on project parser-app: Could not resolve dependencies for project project_group:A:jar:0.1-SNAPSHOT: Could not find artifact project_group:B:jar:0.1-SNAPSHOT

The project structure is as follows:

/pom.xml
/A/pom.xml
/B/pom.xml

The parent pom is as follows:

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>project_group</groupId>
  <artifactId>parent</artifactId>
  <packaging>pom</packaging>
  <version>0.1-SNAPSHOT</version>
  <name>parent</name>

  <modules>
    <module>A</module>
    <module>B</module>
  </modules>

The first child module (the one failing to resolve the dependency):

    <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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>parent_group</groupId>
    <artifactId>parent</artifactId>
    <version>0.1-SNAPSHOT</version>
  </parent>
  <artifactId>A</artifactId>
  <packaging>jar</packaging>
  <name>A</name>

  <dependencies>
    <dependency>
      <groupId>parent_group</groupId>
      <artifactId>B</artifactId>
      <version>0.1-SNAPSHOT</version>
    </dependency>

The second child module (the dependency):

  <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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>parent_group</groupId>
    <artifactId>parent</artifactId>
    <version>0.1-SNAPSHOT</version>
  </parent>
  <artifactId>B</artifactId>
  <packaging>jar</packaging>
  <name>B</name>
4
javamavenjarclasspathpom.xml
try interchanging the build structure, I mean rewrite your pom.xml to have <module>B</module> <module>A</module>. classes in module A needs classes from module B, then B has to be built first – Saurabh Jhunjhunwala
no change, as far as I knew the reactor should work out the order from the dependencies – Benjamin George Roberts
Correct the reactor should handle the order of building. No manuall handling needed nor should it be done. – khmarbaise
Possible duplicate of Maven doesn't recognize sibling modules when running mvn dependency:tree – sschuberth

4 Answers

88
votes

Have you run mvn clean install at least once on the project to install the dependencies within your local repository?

20
votes

The Maven reactor is weird that way, it keeps modules around only for certain tasks. When running a build target that only does something for one subproject, then even if Maven builds dependencies first, it does not keep them around in the reactor (sometimes).

Installing to the local repository is a workaround, but it is horrible and should be avoided when possible, because you can easily end up with outdated build results.

A slightly less ugly workaround is to combine two build targets, where the second build target does something harmless, but triggers addition to reactor in all subprojects.

As an example you can combine the task you want with the 'compile' or 'package' tasks.

Also see highest voted answer at Maven doesn't recognize sibling modules when running mvn dependency:tree

1
votes

This error might also be caused by Maven being in offline mode.

Sometimes I seem to accidentally enable offline mode in IntelliJ IDEA. To disable it, toggle the Toggle Offline Mode toggle in the Maven Toolbar

enter image description here

or uncheck the Work Offline checkbox in the settings under Build, Execution, Deployment > Build Tools > Maven.

enter image description here

0
votes

Configuring test-jar in the jar plugin resolved the issue for me:

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.2.0</version>
        <executions>
          <execution>
            <goals>
              <goal>test-jar</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

Afterwards, running mvn clean install works.