Use StringBuffer to assemble String.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@271614 13f79535-47bb-0310-9956-ffa450edef68

proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/util/ChainReaderHelper.java

@@ -211,16 +211,21 @@ public final class ChainReaderHelper {
         final char[] buffer = new char[bufferSize];
         int bufferLength = 0;
         String text = null;
+        StringBuffer textBuffer = null;
         while (bufferLength != -1) {
             bufferLength = rdr.read(buffer);
             if (bufferLength != -1) {
-                if (text == null) {
-                    text = new String(buffer, 0, bufferLength);
+                if (textBuffer == null) {
+                    textBuffer = new StringBuffer(
+                                    new String(buffer, 0, bufferLength));
                 } else {
-                    text += new String(buffer, 0, bufferLength);
+                    textBuffer.append(new String(buffer, 0, bufferLength));
                 }
             }
         }
+        if (textBuffer != null) {
+            text = textBuffer.toString();
+        }
         return text;
     }
 }