Initially discussed in #178.

Allows adding an already encoded UTF-8 string directly without
having to convert to a ``String`` first.

Change-Id: I23f9c738eec18fd35f4c14f58dbd0f6cf0970dc7

java/com/google/flatbuffers/FlatBufferBuilder.java

@@ -262,6 +262,21 @@ public class FlatBufferBuilder {
         return endVector();
     }
 
+   /**
+    * Encode the string {@code s} in the buffer using UTF-8.
+    *
+    * @param s An already encoded UTF-8 string
+    * @return The offset in the buffer where the encoded string starts
+    */
+    public int createString(ByteBuffer s) {
+        int length = s.remaining();
+        addByte((byte)0);
+        startVector(1, length, 1);
+        bb.position(space -= length);
+        bb.put(s);
+        return endVector();
+    }
+
    /**
     * Should not be creating any other object, string or vector
     * while an object is being constructed