需要帮助解决奇怪的 Class#getResource() 问题 [英] Need help with strange Class#getResource() issue

问题描述

我有一些从现有 jar 读取配置文件的遗留代码，例如:

I have some legacy code that reads a configuration file from an existing jar, like:

URL url = SomeClass.class.getResource("/configuration.properties");
// some more code here using url variable
InputStream in = url.openStream();

显然它以前工作过，但是当我执行此代码时，URL 有效，但我在第三行收到 IOException，说它找不到该文件.该 url 类似于file:jar:c:/path/to/jar/somejar.jar!configuration.properties"，因此它看起来不像是类路径问题 - java 很清楚在哪里可以找到文件..

Obviously it worked before but when I execute this code, the URL is valid but I get an IOException on the third line, saying it can't find the file. The url is something like "file:jar:c:/path/to/jar/somejar.jar!configuration.properties" so it doesn't look like a classpath issue - java knows pretty well where the file can be found..

以上代码是蚂蚁任务的一部分，在任务执行时失败.

The above code is part of an ant task and it fails while the task is executed.

奇怪 - 我将代码和 jar 文件复制到一个单独的类中，它按预期工作，属性文件是可读的.

Strange enough - I copied the code and the jar file into a separate class and it works as expected, the properties file is readable.

在某些时候我将蚂蚁任务的代码更改为

At some point I changed the code of the ant task to

URL url = SomeClass.class.getResource("/configuration.properties");
// some more code here using url variable
InputStream in = SomeClass.class.getResourceAsStream("/configuration.properties");

现在它可以工作了 - 直到它在另一个实现了类似访问模式的类中崩溃..

and now it works - just until it crashes in another class where a similiar access pattern is implemented..

为什么它以前可以工作，为什么现在失败了?我目前看到的唯一区别是，旧版本是使用 Java 1.4 完成的，而我现在正在尝试使用 Java 6.

Why could it have worked before, why does it fail now? The only difference I see at the moment is, that the old build was done with java 1.4 while I'm trying it with Java 6 now.

解决方法

今天我在构建服务器上安装了 Java 1.4.2_19 并让 ant 使用它.令我完全沮丧的惊讶:问题消失了.在我看来，Java 1.4.2 可以处理这种类型的 URL，而 Java 1.6 不能(至少在我的上下文/环境中).

Today I installed Java 1.4.2_19 on the build server and made ant to use it. To my totally frustrating surprise: The problem is gone. It looks to me, that java 1.4.2 can handle URLs of this type while Java 1.6 can't (at least in my context/environment).

我仍然希望得到一个解释，尽管我面临着重写部分代码以使用表现更稳定的 Class#getRessourceAsStream 的工作......

I'm still hoping for an explanation although I'm facing the work to rewrite parts of the code to use Class#getRessourceAsStream which behaved much more stable...

推荐答案

ClassLoader.getResourceAsStream 的典型实现是:

public InputStream getResourceAsStream(String name) {
    URL url = getResource(name);
    try {
        return url != null ? url.openStream() : null;
    } catch (IOException e) {
        return null;
    }
}

Class.getResource 和 getResourceAsStream 的行为彼此相同.

Class.getResource and getResourceAsStream behave the same as each other.

所以看起来要么您使用了一个奇怪且损坏的 ClassLoader 子类，要么您这边的测试中存在一些错误.

So it looks like either you are using a strange and broken subclass of ClassLoader, or there is some mistake in the tests on your side.

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