使用JSONObject.optString作为JSON清理程序时是否安全？

Question

    @Test
    public void test() throws Exception{
        ScriptEngineManager  manager =  new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("JavaScript");

        JSONObject json = new org.json.JSONObject(org.apache.commons.io.FileUtils.readFileToString(new File("c:\\temp\\json.txt")));
        String xx= json.optString("xx");
        engine.eval("var yy = " + xx + ".yy;");
        Object output = engine.get("yy");
    }

json.txt喜欢

{
  xx: {
    inject1: "(function(){java.lang.Runtime.getRuntime().exit(0)})()",
    yy: {
       inject1: "something injected"
    }
  }
}

optString将返回双引号字符串，因此它对于eval函数是否绝对安全？