将文件加载为InputStream的不同方法 [英] Different ways of loading a file as an InputStream

问题描述

有什么区别：

InputStream is = this.getClass().getClassLoader().getResourceAsStream(fileName)

和

InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName)

and

InputStream is = this.getClass().getResourceAsStream(fileName)

每个人哪一个比其他人更适合使用？

When are each one more appropriate to use than the others?

我想读的文件在类路径中作为我的类读取文件。我的类和文件在同一个jar中并打包在一个EAR文件中，并部署在WebSphere 6.1中。

The file that I want to read is in the classpath as my class that reads the file. My class and the file are in the same jar and packaged up in an EAR file, and deployed in WebSphere 6.1.

推荐答案

那里关于如何解释你传递的 fileName 的细微差别。基本上，您有两种不同的方法： ClassLoader.getResourceAsStream（）和 Class.getResourceAsStream（）。这两种方法将以不同的方式定位资源。

There are subtle differences as to how the fileName you are passing is interpreted. Basically, you have 2 different methods: ClassLoader.getResourceAsStream() and Class.getResourceAsStream(). These two methods will locate the resource differently.

在 Class.getResourceAsStream（path）中，路径被解释为您调用它的类的包本地路径。例如，调用 String.getResourceAsStream（myfile.txt）将在以下位置的类路径中查找文件：java / lang /myfile.txt。如果您的路径以 / 开头，那么它将被视为绝对路径，并将从类路径的根开始搜索。所以调用 String.getResourceAsStream（/ myfile.txt）将查看类路径中的以下位置 ./ myfile.txt 。

In Class.getResourceAsStream(path), the path is interpreted as a path local to the package of the class you are calling it from. For example calling, String.getResourceAsStream("myfile.txt") will look for a file in your classpath at the following location: "java/lang/myfile.txt". If your path starts with a /, then it will be considered an absolute path, and will start searching from the root of the classpath. So calling String.getResourceAsStream("/myfile.txt") will look at the following location in your class path ./myfile.txt.

ClassLoader.getResourceAsStream（path）将所有路径视为绝对路径。所以调用 String.getClassLoader（）。getResourceAsStream（myfile.txt）和 String.getClassLoader（）。getResourceAsStream（/ myfile.txt ）将在以下位置的类路径中查找文件： ./ myfile.txt 。

ClassLoader.getResourceAsStream(path) will consider all paths to be absolute paths. So calling String.getClassLoader().getResourceAsStream("myfile.txt") and String.getClassLoader().getResourceAsStream("/myfile.txt") will both look for a file in your classpath at the following location: ./myfile.txt.

每当我在这篇文章中提到一个位置时，它可能是你文件系统本身的一个位置，或者在相应的jar文件中，取决于你从中加载资源的Class和/或ClassLoader。

Everytime I mention a location in this post, it could be a location in your filesystem itself, or inside the corresponding jar file, depending on the Class and/or ClassLoader you are loading the resource from.

在您的情况下，您从Application Server加载类，因此您应该使用 Thread.currentThread（）。getContextClassLoader（）。getResourceAsStream（fileName） 而不是 this.getClass（）。getClassLoader（）。getResourceAsStream（fileName）。 this.getClass（）。getResourceAsStream（）也可以。

In your case, you are loading the class from an Application Server, so your should use Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName) instead of this.getClass().getClassLoader().getResourceAsStream(fileName). this.getClass().getResourceAsStream() will also work.

读本文有关该特定问题的更多详细信息。

Read this article for more detailed information about that particular problem.

其中一个答案是这个问题表明我对Tomcat 7的解释似乎不正确。我试着四处看看为什么会出现这种情况。

One of the answers to this question states that my explanation seems to be incorrect for Tomcat 7. I've tried to look around to see why that would be the case.

所以我看了在Tomcat的 WebAppClassLoader 的源代码中，有几个版本的Tomcat。 findResource（String name）（它对生成所请求资源的URL非常负责）的实现在Tomcat 6和Tomcat 7中几乎完全相同，但在Tomcat中有所不同8。

So I've looked at the source code of Tomcat's WebAppClassLoader for several versions of Tomcat. The implementation of findResource(String name) (which is utimately responsible for producing the URL to the requested resource) is virtually identical in Tomcat 6 and Tomcat 7, but is different in Tomcat 8.

在版本6和7中，实现不会尝试规范化资源名称。这意味着在这些版本中， classLoader.getResourceAsStream（/ resource.txt）可能不会产生与 classLoader.getResourceAsStream（resource相同的结果.txt）虽然它应该是事件（因为那是Javadoc指定的）。 [源代码]

In versions 6 and 7, the implementation does not attempt to normalize the resource name. This means that in these versions, classLoader.getResourceAsStream("/resource.txt") may not produce the same result as classLoader.getResourceAsStream("resource.txt") event though it should (since that what the Javadoc specifies). [source code]

在版本8中，资源名称已规范化，以保证资源名称的绝对版本是使用的名称。因此，在Tomcat 8中，上述两个调用应始终返回相同的结果。 [源代码]

In version 8 though, the resource name is normalized to guarantee that the absolute version of the resource name is the one that is used. Therefore, in Tomcat 8, the two calls described above should always return the same result. [source code]

因此，在使用 ClassLoader.getResourceAsStream（）或 Class.getResourceAsStream（）。您还必须记住 class.getResourceAsStream（/ resource.txt）实际上调用 classLoader.getResourceAsStream（resource.txt）（领先的 / 被剥离了。

As a result, you have to be extra careful when using ClassLoader.getResourceAsStream() or Class.getResourceAsStream() on Tomcat versions earlier than 8. And you must also keep in mind that class.getResourceAsStream("/resource.txt") actually calls classLoader.getResourceAsStream("resource.txt") (the leading / is stripped).

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