ADDITIONAL SYSTEM INFORMATION :
java version "1.8.0_201"
Java(TM) SE Runtime Environment (build 1.8.0_201-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.201-b09, mixed mode)

A DESCRIPTION OF THE PROBLEM :
PlusSign Use URLDecoder Class Return Black Space
But Browse Decoder PlusSign Return PlusSign

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Main the run this code

String decodeStr = URLDecoder.decode("+", "UTF-8");
System.out.println(decodeStr.equals("+"));

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
plus sign
ACTUAL -
blank space

---------- BEGIN SOURCE ----------
String decodeStr = URLDecoder.decode("+", "UTF-8");
System.out.println(decodeStr.equals("+"));
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
find java.net.URLDecoder
150 row
editor sb.append(' '); modify to sb.append('+');