Custom maven assembly

Question

I\'m starting to work with Maven but am not yet successfully thinking in Maven\'s terms. I have a specific requirement and the docs aren\'t giving me enough clues, so I coul

Answer 1

I'm starting to work with Maven but am not yet successfully thinking in Maven's terms.

Welcome on board, Carl! :D

I want to fire this assembly up from the command line (only), hence no need to tie to a phase (or goal? mojo?). Preferrably using either assembly:assembly or assembly:single.

Just to clarify: the build lifecycle itself is made of phases (compile, test, package, etc) and plugin goals (technically Mojos) are bound on phases. You then either invoke a phase... or just a specific plugin goal.

Do I need a custom assembly descriptor for this?

Well, since you want behavior that the pre-defined descriptors don't cover, yes. You'll even need two of them (of for the uberjar, one for the zip).

And is it true I can't nest it in the pom.xml? So it goes in src/assembly/something.xml and gets referenced with a descriptorRef?

Yes, that's true (descriptors use a custom format) and they usually go into src/main/assembly. And no, descriptorRef is for the built-in descriptors, you'll have to use descriptor here.

Can I code this as two relatively simple assemblies, of which one builds on the other (i.e. the .Zip assembly uses the .Jar assembly) or do I have to do everything in one assembly?

As hinted, you'll need two assembly descriptors. Let me help a bit...

Let's assume you have the following project structure:

$ tree .
.
├── pom.xml
└── src
    ├── main
    │   ├── assembly
    │   │   ├── jar.xml
    │   │   └── zip.xml
    │   ├── java
    │   │   └── com
    │   │       └── stackoverflow
    │   │           └── App.java
    │   └── resources
    │       └── log4j.properties
    └── test
        └── java
            └── com
                └── stackoverflow
                    └── AppTest.java

Where the pom.xml contains the following configuration for the assembly plugin:

  ...
  
    ...
  
  ...
  
    
      
        maven-assembly-plugin
        2.2-beta-5
        
          
            src/main/assembly/jar.xml
            src/main/assembly/zip.xml
          
        
      
    
  

The descriptor for the "filtered" uberjar (jar.xml) looks like this:

  uberjar
  
    jar
  
  false
  
    
      true
      runtime
      false
    
  
  
    
      ${project.build.outputDirectory}
      /
      
        log4j.properties
      
    
  

What this descriptor does is (in short):

• include the dependencies, unpack them, but exclude the project itself (yes, this is counter intuitive but this weird default behavior has been kept for backward compatibility)
• include the project files but exclude some of them.

And the descriptor for the zip (zip.xml) looks like this:

  bin
  
    zip
  
  false
  
    
      ${project.basedir}/src/main/resources
      
      
        log4j.properties
      
    
    
      ${project.build.directory}
      
      
        *-uberjar.jar
      
    
  

Which is (somehow) self explaining :)

• it includes the configuration files (relatively to ) at the root of the assembly
• it includes the uberjar (relatively to ) at the root of the assembly

Finally, just run mvn assembly:assembly (that's the goal intended to be used on the CLI).

---

I didn't (knowingly) include META-INF/maven/** in the assembly for the uberjar. Is there a simple way to prevent inclusion of these?

These are coming from the libraries that are unpacked. You can exclude them using unpackOptions. Here is a modified version of the jar.xml:

  uberjar
  
    jar
  
  false
  
    
      true
      runtime
      
        
          META-INF/maven/**
        
      
      false
    
  
  
    
      ${project.build.outputDirectory}
      /
      
        log4j.properties