import org.sonatype.aether.AbstractRepositoryListener; //导入依赖的package包/类
/**
 * Returns a repository listener with no overrides.
 */
@Override
public AbstractRepositoryListener listener() {
  return new AbstractRepositoryListener() {};
}
 

import org.sonatype.aether.AbstractRepositoryListener; //导入依赖的package包/类
/**
 * Returns a repository listener that prints message on artifact resolution
 * and download.
 */
@Override
public AbstractRepositoryListener listener() {
  return listener;
}
 

import org.sonatype.aether.AbstractRepositoryListener; //导入依赖的package包/类
/**
 * Returns a repository listener which will receive artifact resolution
 * progress.
 */
public abstract AbstractRepositoryListener listener();