add alternate links support

src/main/java/cz/jiripinkas/jsitemapgenerator/WebPage.java

@@ -6,6 +6,7 @@
 
 public class WebPage implements Comparable<WebPage> {
     private String name;
+    private Map<String, String> alternateNames;
     private Date lastMod;
     private ChangeFreq changeFreq;
     private Double priority;
@@ -22,6 +23,14 @@ public WebPage addImage(Image image) {
         return this;
     }
 
+    public WebPage addAlternateName(String language, String name) {
+        if (alternateNames == null) {
+            alternateNames = new HashMap<>();
+        }
+        alternateNames.put(language, name);
+        return this;
+    }
+
     public List<Image> getImages() {
         return images;
     }
@@ -50,6 +59,10 @@ public void setName(String name) {
         this.name = name;
     }
 
+    public void setAlternateNames(Map<String, String> alternateNames) {
+        this.alternateNames = alternateNames;
+    }
+
     public void setLastMod(Date lastMod) {
         this.lastMod = lastMod;
     }
@@ -69,6 +82,10 @@ public String getName() {
         return name;
     }
 
+    public Map<String, String> getAlternateNames() {
+        return alternateNames;
+    }
+
     public Date getLastMod() {
         return lastMod;
     }
@@ -152,6 +169,18 @@ public WebPageBuilder name(String ... nameAndDirs) {
             return this;
         }
 
+        /**
+         * Sets WebPage alternate name
+         *
+         * @param language Alternate language
+         * @param name     Name
+         * @return this
+         */
+        public WebPageBuilder alternateName(String language, String name) {
+            webPage.addAlternateName(language, name);
+            return this;
+        }
+
         /**
          * Sets prefix dir to name. Final name will be "dirName/name"
          * @param dirName Dir name

src/main/java/cz/jiripinkas/jsitemapgenerator/generator/SitemapGenerator.java

@@ -9,16 +9,13 @@
 
 import java.net.MalformedURLException;
 import java.net.URL;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.Collections;
+import java.util.*;
 import java.util.function.Function;
 
 public class SitemapGenerator extends AbstractSitemapGenerator {
 
     public enum AdditionalNamespace {
-        IMAGE
+        IMAGE, XHTML
     }
 
     private StringBuilder additionalNamespacesStringBuilder = new StringBuilder();
@@ -48,9 +45,14 @@ public SitemapGenerator(String baseUrl) {
     @Deprecated
     public SitemapGenerator(String baseUrl, AdditionalNamespace[] additionalNamespaces) {
         this(baseUrl);
-        if (Arrays.asList(additionalNamespaces).contains(AdditionalNamespace.IMAGE)) {
+
+        List<AdditionalNamespace> additionalNamespaceList = Arrays.asList(additionalNamespaces);
+        if (additionalNamespaceList.contains(AdditionalNamespace.IMAGE)) {
             additionalNamespacesStringBuilder.append(" xmlns:image=\"http://www.google.com/schemas/sitemap-image/1.1\" ");
         }
+        if (additionalNamespaceList.contains(AdditionalNamespace.XHTML)) {
+            additionalNamespacesStringBuilder.append(" xmlns:xhtml=\"http://www.w3.org/1999/xhtml\" ");
+        }
     }
 
     /**
@@ -148,21 +150,24 @@ String constructUrl(WebPage webPage) {
         StringBuilder out = new StringBuilder();
         out.append("<loc>");
         try {
-            if (webPage.getName() != null) {
-                String wpName = webPage.getName();
-                if (baseUrl.endsWith("/")) {
-                    while (wpName.startsWith("/")) {
-                        wpName = wpName.substring(1);
-                    }
-                }
-                out.append(escapeXmlSpecialCharacters(new URL(baseUrl + wpName).toString()));
-            } else {
-                out.append(escapeXmlSpecialCharacters(new URL(baseUrl).toString()));
-            }
+            out.append(toUrl(baseUrl, webPage.getName()));
         } catch (MalformedURLException e) {
             throw new InvalidUrlException(e);
         }
         out.append("</loc>\n");
+        if (webPage.getAlternateNames() != null) {
+            try {
+                for (Map.Entry<String, String> entry : webPage.getAlternateNames().entrySet()) {
+                    out.append("<xhtml:link rel=\"alternate\" hreflang=\"");
+                    out.append(escapeXmlSpecialCharacters(entry.getKey()));
+                    out.append("\" href=\"");
+                    out.append(toUrl(baseUrl, entry.getValue()));
+                    out.append("\"/>\n");
+                }
+            } catch (MalformedURLException e) {
+                throw new InvalidUrlException(e);
+            }
+        }
         if (webPage.getLastMod() != null) {
             out.append("<lastmod>");
             out.append(dateFormat.format(webPage.getLastMod()));
@@ -181,6 +186,18 @@ String constructUrl(WebPage webPage) {
         return out.toString();
     }
 
+    private String toUrl(String baseUrl, String name) throws MalformedURLException {
+        if (name == null) {
+            return escapeXmlSpecialCharacters(new URL(baseUrl).toString());
+        }
+        if (baseUrl.endsWith("/")) {
+            while (name.startsWith("/")) {
+                name = name.substring(1);
+            }
+        }
+        return escapeXmlSpecialCharacters(new URL(baseUrl + name).toString());
+    }
+
     /**
      * Add single page to sitemap
      *

src/test/java/cz/jiripinkas/jsitemapgenerator/generator/SitemapGeneratorTest.java

@@ -62,6 +62,14 @@ public void testConstructUrlNotEmptyPage() {
 		Assert.assertEquals("<loc>http://www.javavids.com/latest.php</loc>\n", url);
 	}
 
+	@Test
+	public void testConstructAlternateUrls() {
+		String url = sitemapGenerator.constructUrl(WebPage.builder().name("latest.php").alternateName("de", "latest-de.php")
+				.alternateName("es", "latest-es.php").build());
+		Assert.assertEquals("<loc>http://www.javavids.com/latest.php</loc>\n<xhtml:link rel=\"alternate\" hreflang=\"de\" href=\"http://www.javavids.com/latest-de.php\"/>\n" +
+				"<xhtml:link rel=\"alternate\" hreflang=\"es\" href=\"http://www.javavids.com/latest-es.php\"/>\n", url);
+	}
+
 	@Test
 	public void testConstructSitemap() throws Exception {
 		String sitemap = sitemapGenerator.constructSitemapString();