Best practice for multiple project setup with m2eclipse

Question

Example scenario: I have 2 projects, "common-project" and "application-project". The application-project depends on the API provided by common-project. There are also 3rd party jars (example guava) used by both projects.

I am trying convert to using maven and m2eclipse, but am unclear on the best approach. Currently, my maven-free setup has the 3rd party jars added as libraries on common-project, and marked as "exported". This way they are inherited by application-project, and I don't have to explicitly add them as libraries on application project. Both projects are under active development, so I would prefer not to have to build a jar of common-project first, then "install" that to my local repository before I can use the new features in application-project.

What is the recommended approach for this type of project layout? I see the following thread touches roughly on the topic: Project in Eclipse that builds a jar used by another project in Eclipse

Thanks

Answer 1

Example scenario: I have 2 projects, "common-project" and "application-project". The application-project depends on the API provided by common-project. There are also 3rd party jars (example guava) used by both projects.

I would create 3 maven projects: a parent aggregating module, a common-project module and an application-project module depending on common-project and declare guava as dependency in the parent module (so that child project will inherit it). Something like this:

$ tree Q3337426
Q3337426
├── application-project
│   ├── pom.xml
│   └── src
│       ├── main
│           └── ...
│       └── test
│           └── ...
├── common-project
│   ├── pom.xml
│   └── src
│       ├── main
│           └── ...
│       └── test
│           └── ...
└── pom.xml

Where the parent pom.xml looks like this:

<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>com.stackoverflow.Q3337426</groupId>
  <artifactId>Q3337426</artifactId>
  <packaging>pom</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>Q3337426 - Root</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>com.google.guava</groupId>
      <artifactId>guava</artifactId>
      <version>r05</version>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  <modules>
    <module>common-project</module>
    <module>application-project</module>
  </modules>
</project>

The pom.xml for the common-project:

<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>
  <parent>
    <artifactId>Q3337426</artifactId>
    <groupId>com.stackoverflow.Q3337426</groupId>
    <version>1.0-SNAPSHOT</version>
  </parent>
  <artifactId>common-project</artifactId>
  <name>Q3337426 - Common Project</name>
  <dependencies/>
</project>

The pom.xml for the application-project:

<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>
  <parent>
    <artifactId>Q3337426</artifactId>
    <groupId>com.stackoverflow.Q3337426</groupId>
    <version>1.0-SNAPSHOT</version>
  </parent>
  <artifactId>application-project</artifactId>
  <name>Q3337426 - Application Project</name>
  <dependencies>
    <dependency>
      <groupId>${project.groupId}</groupId>
      <artifactId>common-project</artifactId>
      <version>${project.version}</version>
    </dependency>
  </dependencies>
</project>

This is the Maven way to organize such a project and will allow to trigger a reactor build from the root project to build everything.

(...) Both projects are under active development, so I would prefer not to have to build a jar of common-project first, then "install" that to my local repository before I can use the new features in application-project.

The m2eclipse plugin can Resolve dependencies from Workspace projects (this is actually the default behavior). So if you import both application-project and common-project, the former would be configured to depend on the sources of common-project (instead of depending on the jar). Changes made to common-project will be immediately visible when using this setup.

This should solve your concern inside the IDE. Outside the IDE, run a reactor build on the top project.