added Gravatar api class

src/zutil/api/Gravatar.java

@@ -0,0 +1,57 @@
+package zutil.api;
+
+import zutil.Hasher;
+
+/**
+ * This class generate Gravatar image urls
+ */
+public class Gravatar {
+    private static final String GRAVATAR_IMG_PREFIX = "https://www.gravatar.com/avatar/";
+
+
+    /**
+     * @param   email   the email assosicated with the avatar
+     * @return a http url as a String that points to a avatar image
+     */
+    public static String getImageUrl(String email){
+        return getImageUrl(email, null, -1);
+    }
+    /**
+     * @param   email   the email assosicated with the avatar
+     * @param   size    the requested image size. default is 80px
+     * @return a http url as a String that points to a avatar image
+     */
+    public static String getImageUrl(String email, int size){
+        return getImageUrl(email, null, size);
+    }
+    /**
+     * @param   email   the email assosicated with the avatar
+     * @param   format  the picture file format. e.g. "jpg", "png"
+     * @return a http url as a String that points to a avatar image
+     */
+    public static String getImageUrl(String email, String format){
+        return getImageUrl(email, format, -1);
+    }
+    /**
+     * @param   email   the email assosicated with the avatar
+     * @param   format  the picture file format. e.g. "jpg", "png"
+     * @param   size    the requested image size. default is 80px
+     * @return a http url as a String that points to a avatar image
+     */
+    public static String getImageUrl(String email, String format, int size){
+        String formatStr = (format!=null ? "."+format : "");
+        String sizeStr   = (size > 0     ? "?size="+size : "");
+        return new StringBuilder(GRAVATAR_IMG_PREFIX)
+                .append(getHash(email))
+                .append(formatStr)
+                .append(sizeStr)
+                .toString();
+    }
+
+
+    private static String getHash(String email){
+        email = (""+email).trim();
+        email = email.toLowerCase();
+        return Hasher.MD5(email);
+    }
+}