In order for the code bellow to work:

► Make sure to update the variables ("solrUrl", "collectionName", ...) with your information.

final String[] solrUrl = { "http://localhost:8983/solr" };

final CloudSolrClient cloudSolrClient = new CloudSolrClient.Builder(Arrays.asList(solrUrl)).build();

final String aliasName = "alias1";
final String aliasedCollections = "collection1,collection2";

// create alias
{
    final CollectionAdminRequest.CreateAlias adminRequest = CollectionAdminRequest.CreateAlias.createAlias(aliasName, aliasedCollections);

    CollectionAdminResponse adminResponse = adminRequest.process(cloudSolrClient);

    System.out.println(adminResponse);
}

cloudSolrClient.close();

final String[] solrUrl = { "http://localhost:8983/solr" };

final CloudSolrClient cloudSolrClient = new CloudSolrClient.Builder(Arrays.asList(solrUrl)).build();

final String aliasName = "alias1";

// delete alias
{
    final CollectionAdminRequest.DeleteAlias adminRequest = CollectionAdminRequest.DeleteAlias.deleteAlias(aliasName);

    CollectionAdminResponse adminResponse = adminRequest.process(cloudSolrClient);

    System.out.println(adminResponse);
}

cloudSolrClient.close();