Write empty sitemap and index files (#23)

* Allow SitemapGenerators to write an empty sitemap.

* Allow SitemapIndexGenerators to write an empty sitemap index.

src/main/java/com/redfin/sitemapgenerator/AbstractSitemapGeneratorOptions.java

@@ -9,6 +9,7 @@ abstract class AbstractSitemapGeneratorOptions<THIS extends AbstractSitemapGener
 	File baseDir;
 	URL baseUrl;
 	String fileNamePrefix = "sitemap";
+	boolean allowEmptySitemap = false;
 	boolean allowMultipleSitemaps = true;
 	String suffixStringPattern; // this will store some type of string pattern suitable per needs.
 	W3CDateFormat dateFormat;
@@ -38,6 +39,17 @@ abstract class AbstractSitemapGeneratorOptions<THIS extends AbstractSitemapGener
 		return getThis();
 	}
 
+	/**
+	 * Permit writing a sitemap that contains no URLs.
+	 *
+	 * @param allowEmpty {@code true} if an empty sitemap is permissible
+	 * @return this instance, for chaining
+	 */
+	public THIS allowEmptySitemap(boolean allowEmpty) {
+		this.allowEmptySitemap = allowEmpty;
+		return getThis();
+	}
+
 	/** When more than the maximum number of URLs are passed in, should we split into multiple sitemaps automatically, or just throw an exception? */
 	public THIS allowMultipleSitemaps(boolean allowMultipleSitemaps) {
 		this.allowMultipleSitemaps = allowMultipleSitemaps;

src/main/java/com/redfin/sitemapgenerator/SitemapGenerator.java

@@ -21,6 +21,7 @@ abstract class SitemapGenerator<U extends ISitemapUrl, THIS extends SitemapGener
 	private final File baseDir;
 	private final String fileNamePrefix;
 	private final String fileNameSuffix;
+	private final boolean allowEmptySitemap;
 	private final boolean allowMultipleSitemaps;
 	private final ArrayList<U> urls = new ArrayList<U>();
 	private final W3CDateFormat dateFormat;
@@ -40,6 +41,7 @@ abstract class SitemapGenerator<U extends ISitemapUrl, THIS extends SitemapGener
 		W3CDateFormat dateFormat = options.dateFormat;
 		if (dateFormat == null) dateFormat = new W3CDateFormat();
 		this.dateFormat = dateFormat;
+		allowEmptySitemap = options.allowEmptySitemap;
 		allowMultipleSitemaps = options.allowMultipleSitemaps;
 		maxUrls = options.maxUrls;
 		autoValidate = options.autoValidate;
@@ -165,7 +167,7 @@ abstract class SitemapGenerator<U extends ISitemapUrl, THIS extends SitemapGener
 	 */
 	public List<File> write() {
 		if (finished) throw new RuntimeException("Sitemap already printed; you must create a new generator to make more sitemaps");
-		if (urls.size() == 0 && mapCount == 0) throw new RuntimeException("No URLs added, sitemap would be empty; you must add some URLs with addUrls");
+		if (!allowEmptySitemap && urls.isEmpty() && mapCount == 0) throw new RuntimeException("No URLs added, sitemap would be empty; you must add some URLs with addUrls");
 		writeSiteMap();
 		finished = true;
 		return outFiles;
@@ -221,7 +223,7 @@ abstract class SitemapGenerator<U extends ISitemapUrl, THIS extends SitemapGener
 		if (baseDir == null) {
 			throw new NullPointerException("To write to files, baseDir must not be null");
 		}
-		if (urls.size() == 0) return;
+		if (urls.isEmpty() && (mapCount > 0 || !allowEmptySitemap)) return;
 		String fileNamePrefix;
 		if (mapCount > 0) {
 			fileNamePrefix = this.fileNamePrefix + mapCount;

src/main/java/com/redfin/sitemapgenerator/SitemapIndexGenerator.java

@@ -19,6 +19,7 @@ import org.xml.sax.SAXException;
 public class SitemapIndexGenerator {
 	private final URL baseUrl;	
 	private final File outFile;
+	private final boolean allowEmptyIndex;
 	private final ArrayList<SitemapIndexUrl> urls = new ArrayList<SitemapIndexUrl>();
 	private final int maxUrls;
 	private final W3CDateFormat dateFormat;
@@ -32,6 +33,7 @@ public class SitemapIndexGenerator {
 		private URL baseUrl;
 		private File outFile;
 		private W3CDateFormat dateFormat = null;
+		private boolean allowEmptyIndex = false;
 		private int maxUrls = MAX_SITEMAPS_PER_INDEX;
 		private Date defaultLastMod = new Date();
 		private boolean autoValidate = false;
@@ -59,6 +61,18 @@ public class SitemapIndexGenerator {
 			this.dateFormat = dateFormat;
 			return this;
 		}
+
+		/**
+		 * Permit writing an index that contains no URLs.
+		 *
+		 * @param allowEmptyIndex {@code true} if an empty index is permissible
+		 * @return this instance, for chaining
+		 */
+		public Options allowEmptyIndex(boolean allowEmptyIndex) {
+			this.allowEmptyIndex = allowEmptyIndex;
+			return this;
+		}
+
 		/**
 		 * The maximum number of sitemaps to allow per sitemap index; the default is the
 		 * maximum allowed (1,000), but you can decrease it if you wish (for testing)
@@ -116,6 +130,7 @@ public class SitemapIndexGenerator {
 	private SitemapIndexGenerator(Options options) {
 		this.baseUrl = options.baseUrl;		
 		this.outFile = options.outFile;
+		this.allowEmptyIndex = options.allowEmptyIndex;
 		this.maxUrls = options.maxUrls;
 		W3CDateFormat dateFormat = options.dateFormat;
 		if (dateFormat == null) dateFormat = new W3CDateFormat();
@@ -206,7 +221,7 @@ public class SitemapIndexGenerator {
 	
 	/** Writes out the sitemap index */
 	public void write() {
-		if (urls.size() == 0) throw new RuntimeException("No URLs added, sitemap index would be empty; you must add some URLs with addUrls");
+		if (!allowEmptyIndex && urls.isEmpty()) throw new RuntimeException("No URLs added, sitemap index would be empty; you must add some URLs with addUrls");
 		try {
 			// TODO gzip? is that legal for a sitemap index?
 			FileWriter out = new FileWriter(outFile);

src/test/java/com/redfin/sitemapgenerator/SitemapGeneratorTest.java

@@ -348,6 +348,24 @@ public class SitemapGeneratorTest extends TestCase {
 		assertEquals("Second string didn't match", SITEMAP_PLUS_ONE, siteMapsAsStrings.get(1));
 	}
 
+	public void testWriteEmptySitemap() throws Exception {
+		wsg = WebSitemapGenerator.builder("http://www.example.com", dir).allowEmptySitemap(true).build();
+		String expected = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
+				"<urlset xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\" >\n" +
+				"</urlset>";
+		String sitemap = writeSingleSiteMap(wsg);
+		assertEquals(expected, sitemap);
+	}
+
+	public void testMaxUrlsAllowingEmptyDoesNotWriteExtraSitemap() throws Exception {
+		wsg = WebSitemapGenerator.builder("http://www.example.com", dir).allowEmptySitemap(true).maxUrls(10).build();
+		for (int i = 0; i < 10; i++) {
+			wsg.addUrl("http://www.example.com/"+i);
+		}
+		String sitemap = writeSingleSiteMap(wsg);
+		assertEquals(SITEMAP1, sitemap);
+	}
+	
 	private String writeSingleSiteMap(WebSitemapGenerator wsg) {
 		List<File> files = wsg.write();
 		assertEquals("Too many files: " + files.toString(), 1, files.size());

src/test/java/com/redfin/sitemapgenerator/SitemapIndexGeneratorTest.java

@@ -87,6 +87,16 @@ public class SitemapIndexGeneratorTest extends TestCase {
 		} catch (RuntimeException e) {}
 	}
 
+	public void testNoUrlsEmptyIndexAllowed() throws Exception {
+		sig = new SitemapIndexGenerator.Options(EXAMPLE, outFile).allowEmptyIndex(true).build();
+		sig.write();
+		String expected = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
+				"<sitemapindex xmlns=\"http://www.sitemaps.org/schemas/sitemap/0.9\">\n" +
+				"</sitemapindex>";
+		String actual = TestUtil.slurpFileAndDelete(outFile);
+		assertEquals(expected, actual);
+	}
+	
 	public void testMaxUrls() throws Exception {
 		sig = new SitemapIndexGenerator.Options(EXAMPLE, outFile).autoValidate(true)
 			.maxUrls(10).defaultLastMod(new Date(0)).dateFormat(ZULU).build();