code: @Override
      public boolean isCharsetSupported(String charset) {
          if (null == charset) {
              return false;
          }
          Boolean supported = this.supportedEncodingsCache.get(charset);
          if (supported != null) {
              return supported.booleanValue();
          }
          try {
              new String(TEST_CHAR, charset);
              supported = Boolean.TRUE;
          } catch (UnsupportedEncodingException e) {
              supported = Boolean.FALSE;
          }
          this.supportedEncodingsCache.put(charset, supported);
          return supported.booleanValue();
      }
docs: /*
  @see com.ibm.websphere.http.EncodingUtils#isCharsetSupported(java.lang.String)