docs: public static boolean isCharsetSupported (String charset){
          Boolean supported = (Boolean) supportedEncodingsCache.get(charset);
          if(supported != null){
              return supported.booleanValue();
          }
          try{
              new String (TEST_CHAR, charset);
              supportedEncodingsCache.put(charset, Boolean.TRUE);
          }catch (UnsupportedEncodingException e){
              if (com.ibm.ejs.ras.TraceComponent.isAnyTracingEnabled()&&logger.isLoggable (Level.FINE)) {
                  logger.logp(Level.FINE, CLASS_NAME,"isCharsetSupported", "Encountered UnsupportedEncoding charset [" + charset +"]");
              }
              supportedEncodingsCache.put(charset, Boolean.FALSE);
              return false;
          }
          return true;
      }