java.lang.ClassNotFoundException: org.slf4j.LoggerFactory Maven - eclipse

Question

I just installed Maven on Eclipse. If I run the pom.xml, I get the error below.
People who use Windows don't get this error. I have Mac OS X.
When I add slf4j-simple-1.7.5.jr and slf4j-api-1.7.5.jar to the build path, it works.
Is there a way NOT to add external jars?
EDIT 2:
I used Maven clean via Terminal and that worked. I think the problem is Maven internal in Eclipse.
EDIT 3:
I deleted the projects and checked out it all from SVN and it worked somehow.
[INFO] Scanning for projects...
[ERROR] Internal error: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException: org/slf4j/LoggerFactory: org.slf4j.LoggerFactory -> [Help 1]
org.apache.maven.InternalErrorException: Internal error: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:168)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:534)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:196)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:141)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at org.eclipse.tycho.core.maven.utils.MavenCompatiblityHelper.getPluginDescriptor(MavenCompatiblityHelper.java:86)
at org.eclipse.tycho.core.maven.utils.PluginRealmHelper.execute(PluginRealmHelper.java:95)
at org.eclipse.tycho.p2.resolver.P2TargetPlatformResolver.getDependencyMetadata(P2TargetPlatformResolver.java:144)
at org.eclipse.tycho.p2.resolver.P2TargetPlatformResolver.setupProjects(P2TargetPlatformResolver.java:126)
at org.eclipse.tycho.core.resolver.DefaultTychoDependencyResolver.setupProject(DefaultTychoDependencyResolver.java:87)
at org.eclipse.tycho.core.maven.TychoMavenLifecycleParticipant.afterProjectsRead(TychoMavenLifecycleParticipant.java:77)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:273)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
... 11 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.eclipse.tycho.core.maven.utils.MavenCompatiblityHelper.getPluginDescriptor(MavenCompatiblityHelper.java:68)
... 18 more
Caused by: java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
at com.ning.http.client.AsyncHttpClient.<clinit>(AsyncHttpClient.java:147)
at org.sonatype.aether.connector.async.AsyncRepositoryConnector.<init>(AsyncRepositoryConnector.java:150)
at org.sonatype.aether.connector.async.AsyncRepositoryConnectorFactory.newInstance(AsyncRepositoryConnectorFactory.java:110)
at org.sonatype.aether.impl.internal.DefaultRemoteRepositoryManager.getRepositoryConnector(DefaultRemoteRepositoryManager.java:333)
at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:456)
at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:220)
at org.sonatype.aether.impl.internal.DefaultArtifactResolver.resolveArtifact(DefaultArtifactResolver.java:197)
at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:268)
at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor(DefaultArtifactDescriptorReader.java:173)
at org.sonatype.aether.impl.internal.DefaultRepositorySystem.readArtifactDescriptor(DefaultRepositorySystem.java:316)
at org.apache.maven.plugin.internal.DefaultPluginDependenciesResolver.resolve(DefaultPluginDependenciesResolver.java:108)
at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getPluginDescriptor(DefaultMavenPluginManager.java:143)
... 23 more
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:50)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:244)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:230)
... 35 more
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/InternalErrorException

Answer 1

If your code makes use of slf4j, you'll also have to add the API and one of the implementation jars to your project. So the answer is: no.