Question

我正在创建一个简单的应用程序，由于某种原因，我一直得到空指针异常。我的猜测是它与我的session.open在if语句中有关？我得到的错误是在finally块上，它表示session.close（）;

<link href="http://freelancezonebd.com/sb-web/3/css/bootstrap.css" rel="stylesheet"/>
<nav class="navbar navbar-inverse navbar-fixed-top">

		<div class="container">
			<div class="navbar-header">
				<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-nav-demo" aria-expanded="false">
					<span class="sr-only">Toggle navigation</span>
					<span class="icon-bar"></span>
					<span class="icon-bar"></span>
					<span class="icon-bar"></span>
				</button>
				<a href="#" class="navbar-brand"><span class="glyphicon glyphicon-picture" aria-hidden="true"></span> IMGS</a>
			</div>
			<div class="collapse navbar-collapse" id="bs-nav-demo">
				<ul class="nav navbar-nav">
					<li><a href="#">About</a></li>
					<li><a href="#">Contact</a></li>
				</ul>
				<ul class="nav navbar-nav navbar-right">
					<li><a href="#">Sign Up</a></li>
					<li><a href="#">Login</a></li>
				</ul>
			</div>
		</div>

	</nav>

....
....


	<script src="https://code.jquery.com/jquery-2.2.1.js"></script>
	<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>

错误：

$("#dragme").draggable({
  // You still need to set a value for containment
  // else it won't be checked when evaluating the position
  containment: 'document',
  start: function(e, ui) {
    // You simply set a left, top, right, bottom coordinates.
    // You need to set it on start so if the elements have been
    // resized, the containment follows.
    var cont = [
      $('#topleft').offset().left + $('#topleft').outerWidth(),
      $('#toprow').offset().top,
      $('#toprow').offset().left + $('#toprow').outerWidth() - ui.helper.width(),
      $('#bottomrow').offset().top + $('#bottomrow').outerHeight() - ui.helper.height(),
    ]

    $(this).draggable('instance').containment = cont;
  }
});

Answer 1

该行上的> pollutantmean <- function(directory, pollutant, id = 1:332) { sum = 0 length = 0 listCSV <- list.files()[id] for (i in listCSV) { data <- read.csv(i) no_missing <- data[!is.na(data$pollutant),] sum = sum + sum(no_missing$pollutant) length = length + length(no_missing$pollulant) } sum/length }，堆栈跟踪中没有其他内容，只能表示NullPointerException为空。据我所知，唯一可能发生的方法是，session赋值是否永远不会执行 - 这意味着session = sessionFactory.openSession();或sessionFactory.openSession()中发生异常，该异常被HibernateUtil.getSessionFactory()块中引发的后一个异常隐藏。

我希望如果您在调试器中单步调试此代码，您会看到执行流程从这两行中的一行跳转到finally块，然后在catch上点击NullPointerException （因为事务分配从未发生过）并跳转到transaction.rollback()块，在那里它命中另一个finally并挽救。

Answer 2

由于session和sessionFactory都在try / catch块之外被初始化为null，所以永远不要假设它们在finally子句中不会为空并且调用{{1直接。将其更改为以下内容：

close()

Hibernate Java中会话的空指针异常

2 个答案: