docs: public int getIsolationLevel(int preferred) {
          int isolationLevel;
          final boolean isTraceOn = TraceComponent.isAnyTracingEnabled(); // d532639.2
  
          if (isTraceOn && tc.isEntryEnabled())
              Tr.entry(tc, "getIsolationLevel: " + preferred);
  
          // First, go get the ContainerTx for the current transaction.
  
          ContainerTx ctx = null;
          try {
              ctx = getCurrentTx(false);//d171654
          } catch (CSITransactionRolledbackException ex) {
              // This would be a Container internal error. Log it and continue.
              FFDCFilter.processException(ex, CLASS_NAME + ".getIsolationLevel",
                                          "1614");
              Tr.error(tc, "IGNORING_UNEXPECTED_EXCEPTION_CNTR0033E", ex);
          }
  
          if (ctx == null) {
              // The Container is not involved in the specified transaction.
              // The call is probably for a JSP/Servlet, so just return the
              // specified defrault.
              if (isTraceOn && tc.isEventEnabled())
                  Tr.event(tc, "ContainerTx is null, returning specified default");
              isolationLevel = preferred;
          } else {
              // The Container is involved in the specified tranaction.
              // Get the isolation level from the ContainerTx object. And, if
              // the value is NONE (either not set yet, or was not specified
              // for the bean method), then set the specified default for the
              // transaction.
              isolationLevel = ctx.getIsolationLevel();
  
              if (isolationLevel == java.sql.Connection.TRANSACTION_NONE) {
                  if (isTraceOn && tc.isEventEnabled())
                      Tr.event(tc, "Using specified default");
  
                  isolationLevel = preferred;
                  try {
                      ctx.setIsolationLevel(isolationLevel);
                  } catch (IsolationLevelChangeException ex) {
                      // This would be a Container internal error.  It would seem to
                      // only be possible if another thread were modifying the
                      // ContainerTx at the same time.  Log it and continue.
                      FFDCFilter.processException(ex, CLASS_NAME + ".getIsolationLevel",
                                                  "1645");
                      Tr.error(tc, "IGNORING_UNEXPECTED_EXCEPTION_CNTR0033E", ex);
                  }
              }
          }
  
          if (isTraceOn && tc.isEntryEnabled())
              Tr.exit(tc, "getIsolationLevel: " +
                          MethodAttribUtils.getIsolationLevelString(isolationLevel));
  
          return isolationLevel;
      }