Replaced String concatenation in loop

Replaced String concatenation in loop with StringBuilder
Unit test added

Signed-off-by: Laszlo Hornyak <laszlo.hornyak@gmail.com>

utils/src/com/cloud/utils/StringUtils.java

@@ -95,17 +95,17 @@ public class StringUtils {
      */
 
     public static String listToCsvTags(List<String> tagsList) {
-        String tags = "";
+        StringBuilder tags = new StringBuilder();
         if (tagsList.size() > 0) {
             for (int i = 0; i < tagsList.size(); i++) {
-                tags += tagsList.get(i);
+                tags.append(tagsList.get(i));
                 if (i != tagsList.size() - 1) {
-                    tags += ",";
+                    tags.append(',');
                 }
             }
         }
 
-        return tags;
+        return tags.toString();
     }
 
     public static String getExceptionStackInfo(Throwable e) {

utils/test/com/cloud/utils/StringUtilsTest.java

@@ -18,6 +18,11 @@ package com.cloud.utils;
 
 import static org.junit.Assert.assertEquals;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import junit.framework.Assert;
+
 import org.junit.Test;
 
 public class StringUtilsTest {
@@ -216,4 +221,10 @@ public class StringUtilsTest {
         String result = StringUtils.cleanString(input);
         assertEquals(result, expected);
     }
+
+    @Test
+    public void listToCsvTags() {
+        Assert.assertEquals("a,b,c", StringUtils.listToCsvTags(Arrays.asList("a","b", "c")));
+        Assert.assertEquals("", StringUtils.listToCsvTags(new ArrayList<String>()));
+    }
 }