Missing builder(org.maven.ide.eclipse.maven2Builder)

Question

I'm using Eclipse Indigo and have the following in my .project file:

<?xml version="1.0" encoding="UTF-8"?> 
  <projectDescription> 
    <name>new project</name> 
    <buildSpec> 
      <buildCommand> 
        <name>org.eclipse.jdt.core.javabuilder</name> 
      </buildCommand> 
      <buildCommand> 
        <name>org.maven.ide.eclipse.maven2Builder</name> 
      </buildCommand> 
    </buildSpec>
    <natures> 
      <nature>org.eclipse.jdt.core.javanature</nature>       
      <nature>org.maven.ide.eclipse.maven2Nature</nature> 
    </natures> 
  </projectDescription>

I have the m2e - Maven Integration for Eclipse installed. But I am getting Missing builder(org.maven.ide.eclipse.maven2Builder) under the Builders properties and I am getting a java.lang.ClassNotFoundException: when I try to running a class file from my project.

I guess I am missing something in the config somewhere or a plugin?

Thanks

Answer 1

It is most likely a mismatch between the declared builder class and your m2e plugin. Try this:

<?xml version="1.0" encoding="UTF-8"?> 
<projectDescription> 
    <name>new project</name> 
    <buildSpec> 
        <buildCommand> 
            <name>org.eclipse.jdt.core.javabuilder</name> 
        </buildCommand> 
        <buildCommand> 
            <name>org.eclipse.m2e.core.maven2Builder</name> 
        </buildCommand> 
    </buildSpec> 
    <natures> 
        <nature>org.eclipse.jdt.core.javanature</nature> 
        <nature>org.eclipse.m2e.core.maven2Nature</nature> 
    </natures> 
</projectDescription>

Please note the different org.eclipse.m2e.core namespace.

Answer 2

While changing to the newer m2e plugin might work, it may not. You can install the older m2e plugin version which uses the old tag in Indigo. See http://m2eclipse.sonatype.org/installing-m2eclipse.html. Unfortunately, you can't have both the old and new installed at once, so if you managed to install the new one, you will have to uninstall it before installing the older version.

Answer 3

@LucaGeretti's answer was exactly my problem, fixing it in Eclipse Indigo can be done easily from the IDE:

1. Right click on your project.
2. Select 'Configure'.
3. Click 'Convert to Maven Project'.