/**
 * Represents a set of Sitemaps, which can be either a UrlSet or an Index.
 * This class provides methods to manage a list of Sitemap objects and determine the type of the SitemapSet.
 *
 */
public class SitemapSet implements Serializable {

    private static final long serialVersionUID = 1L;

    /** Constant for UrlSet type. */
    public static final String URLSET = "UrlSet";

    /** Constant for Index type. */

### Build and Test
```bash
# Clean build and run tests
mvn clean test

# Full build with packaging
mvn clean package

# Run tests only
mvn test

# Run specific tests
mvn test -Dtest=CurlTest
mvn test -Dtest=CurlRequestTest
mvn test -Dtest=CurlResponseTest
mvn test -Dtest=CurlExceptionTest
```

### Code Quality
```bash
# Format code (using external formatter config)
mvn formatter:format

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
   <url>
      <loc>http://www.example.com/</loc>
      <lastmod>2005-01-01</lastmod>
      <changefreq>monthly</changefreq>
      <priority>0.8</priority>
   </url>
   <url>
      <loc>http://www.example.com/catalog?item=12&amp;desc=vacation_hawaii</loc>
      <changefreq>weekly</changefreq>
   </url>
   <url>

            robotTxtFile.deleteOnExit();

            // sitemaps.xml
            buf = new StringBuilder();
            buf.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>").append('\n');
            buf.append("<urlset ").append("xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">").append('\n');
            buf.append("<url>").append('\n');
            buf.append("<loc>http://localhost:7070/index.html</loc>").append('\n');

            robotTxtFile.deleteOnExit();

            // sitemaps.xml
            buf = new StringBuilder();
            buf.append("<?xml version=\"1.0\" encoding=\"UTF-8\"?>").append('\n');
            buf.append("<urlset ").append("xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">").append('\n');
            buf.append("<url>").append('\n');
            buf.append("<loc>http://localhost:7070/index.html</loc>").append('\n');