MyClass.class.getClassLoader（）。getResource（""）。getPath（）抛出NullPointerException [英] MyClass.class.getClassLoader().getResource("").getPath() throws NullPointerException

问题描述

我的代码在开发计算机上正常运行，但在生产环境中安装时会抛出NullPointerException。抛出异常的行如下：

I have code that is running correctly on a development machine but throws a NullPointerException when installed in a production environment. The line that throws the exception is the following:

MyClass.class.getClassLoader().getResource("").getPath();

所以我把它分成多行代码，看看究竟哪个调用返回null，如下所示：

So I split this into multiple lines of code to see exactly which call was returning null, like this:

ClassLoader cl = MyClass.class.getClassLoader();
URL url = cl.getResource("");
String path = url.getPath();

现在url.getPath（）调用抛出NullPointerException，意味着cl.getResource（ ）返回null。

Now the url.getPath() call is throwing the NullPointerException, meaning that cl.getResource("") is returning null.

有谁能告诉我这个调用怎么会返回null？

Can anyone tell me how this call can ever return null?

推荐答案

对于不同的 ClassLoader 实现， getResource 的实现是不同的。

The implementation of getResource is different for different ClassLoader implementations.

虽然这可能在本地机器上可靠地工作，但不能保证在其他ClassLoader实现上成功。

While this might reliably work on your local machine, it is not guaranteed to be successful on other ClassLoader implementations.

所以期待其他ClassLoader表现不同（特别是如果您在Application Server，WebStart Launcher或任何具有某些安全限制的环境中执行该代码）。

So expect other ClassLoaders to behave differently (especially if you execute that code inside a Application Server, WebStart Launcher or any environment that has some security restrictions).

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