Re: How to deal with transitive maven dependencies?

Hello Thomas,

thank you very much, but I only understand parts of your posts, because maven is still new to me...

Actually, nothing. Nothing on the Maven side though.

Yes, I can validate this by doing mvn gwt:devmode and the app works, nevertheless what eclipse thinks is wrong...

 

The problem is with M2Eclipse, but I don't know it enough to know how you're supposed to work with it and give you any guidance here.

Well, I was used to do everything in eclipse: create gwt project, compile, run, debug, ... I just migrated one general library (pure java and gwt code) and two apps (which I recreated with webAppCreator -templates maven) to maven.

When I make changes to the library, I execute mvn clean compile package install. I feel that some of these goals should be triggered by others, but I call them all to make sure to end up in a defined state.

When I make changes to one of the apps, I execute mvn clean compile package gwt:devmode.

I know that all these goals must be redundant and triggered by each other somehow, but during the migration of my projects I have seen many problems that disappeared when repeating the different maven goals...

The problem is that "mvn war:war" is somehow invoked (do you invoke it yourself manually, from within Eclipse? possibly as "mvn package") and it resolves its dependencies from the workspace (by default at least), similar to a reactor build.

To reproduce the problem I don't need to call anything: I simply open the pom.xml in eclipse, remove the "provided" scope, and save the pom.xml file. Then, immediately, the error marker appears.

BTW: I don't know "reactor builds", so I cannot follow your additional words:

 

But when resolving the library, it won't build/package it! and Maven's default behavior when trying to resolve unpackaged dependencies from a reactor build, is to take target/classes if the dependency has <packaging>jar</packaging>

This can happen in regular reactor builds when you e.g. run "mvn test": it'll run "mvn test" on the first submodule, then "mvn test" on the second submodule, and if the second submodule depends on the first one, then its target/classes is used (because "test" comes before "package" in the lifecycle). This is a design flaw in Maven (if you ask me), and one of the reasons I generally recommend using other builds tools (e.g. Gradle) instead.

If you disable resolution of dependencies from the workspace in Eclipse, then the "mvn war:war" will resolve the library from the local repository instead (which means you'd have to "mvn install" the library to have the app see the changes).

The only thing I understand in this paragraph is that I have to "mvn install" the library, what I am actually doing, so that the apps can see it.

Since my app works when doing everything on the command line, the only thing I want is that the error markers disappear (assuming that they are false positives)...

 

My (personal) recommendation is to work with reactor (multi-module) builds, to only ever execute Maven commands on the root module, and to only ever use the "package" and "verify" lifecycle phases (and possibly "install" and/or "deploy" if you really need them).

I would like to follow this recommendation, but what exactly do I have to do?

This is one reason I built the net.ltgt.gwt.maven:gwt-maven-plugin, because the old org.codehaus.mojo:gwt-maven-plugin could work that way.

This is one big questionmark for me! I am evaluating the different GWT maven plugins for a while, and I learned that yours is the one that is recommended. Then, I found that webAppCreator -templates maven creates a project template that I can work with. And I noticed net.ltgt.gwt.maven in the pom.xml. Therefore, I thought that I am using your plugin. But the error message discussed here is a "MojoExecutionException". The word "Mojo" seems to refer to the other plugin. That's confusing to me. Can you resolve this?

Magnus

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