在嵌套JAR内的文件夹中查找文件名

问题描述：

当我的应用程序打包为JAR时，我无法到达目标文件夹"images". 我得到的不是单个文件，我想要的是图像"文件夹中所有.jpg文件的列表.

I'm having trouble reaching a target folder "images" when my application is packaged as a JAR. I am not after getting a single file, what I want is a list of all the .jpg files in the "images" folder.

我已经尝试过了: URI uri = getClass().getClassLoader.getResource("images").toURI();

这将返回:jar:file:/C:/test-1.0-SNAPSHOT.jar!/BOOT-INF/lib/core-1.0-SNAPSHOT.jar!/images

然后，我尝试创建一个流来迭代这样的文件:

Then i tried to create a stream to iterate over the files like this:

FileSystem fs = FileSystems.newFilesSystem(uri, Collections.emptyMap());
Path p = fs.getPath("images");
Files.walk(p).forEach(path -> System.out.println(path));

这只是给med一个FileNotFoundException.

This just gives med a FileNotFoundException.

那么，如何访问嵌套JAR内的"images"文件夹?

So, how can I access the "images" folder inside my nested JARs?

这不是以下内容的重复:如何列出JAR文件中的文件?.我已经尝试了所有的东西.不同之处在于我在另一个JAR(嵌套JAR)中有一个JAR.这就是造成我相信的问题的原因.

This is not duplicate of: How to list the files inside a JAR file?. I have tried every thing in there. The difference is that i have a JAR INSIDE another JAR, nested JARs. This is what is creating the issue i believe.

答

在JDK 12之前，完全不支持内置ZipFileSystem中的嵌套jar文件.

Prior to JDK 12, there is no support for nested jar files in the builtin ZipFileSystem at all.

例如，ZipFileSystemProvider接受Path的newFileSystem方法具有类似

E.g., the newFileSystem method of ZipFileSystemProvider accepting a Path has a statement like

if (path.getFileSystem() != FileSystems.getDefault()) {
    throw new UnsupportedOperationException();
}

即使对于JDK 12，由于对jar: URL的持续误操作，获取嵌套zip文件系统也不容易.

Even for JDK 12, getting hands on nested zip filesystems is not easy due to a consistent mistreatment of jar: URLs.

jar: URL的语法已指定为:

jar:<url>!/{entry}

这意味着您资源的正确URL将是

which implies that the correct URL for your resource would be

outer file                file:/C:/test-1.0-SNAPSHOT.jar
nested jar file       jar:file:/C:/test-1.0-SNAPSHOT.jar!/BOOT-INF/lib/core-1.0-SNAPSHOT.jar
entry of nested   jar:jar:file:/C:/test-1.0-SNAPSHOT.jar!/BOOT-INF/lib/core-1.0-SNAPSHOT.jar!/images

要解析这样的URL，您必须使用第一个jar:和最后一个!/之间的部分提取jar文件的位置，然后递归地对其进行解析. 但是，我见过的所有JDK代码，无论是支持URL API还是FileSystem API都始终失败，使用indexOf("!/")而不是lastIndexOf("!/"). 因此，嵌套的jar: URI/URL根本不起作用.

To parse such a URL, you would have to extract the location of the jar file using the part between the first jar: and the last !/ and recursively parse that. However, all JDK code I’ve seen, regardless of backing the URL API or the FileSystem API consistently fails to do so, using indexOf("!/") rather then lastIndexOf("!/"). So nested jar: URIs/URLs simply don’t work.

使用嵌套文件系统的唯一方法是使用已经与FileSystem关联的Path实例打开它们:

The only way to get hands on a nested file system is to open them using Path instances already associated with a FileSystem:

Path outer = Paths.get("C:", "test-1.0-SNAPSHOT.jar");
ClassLoader cl = null;
try(FileSystem outerFs = FileSystems.newFileSystem(outer, cl);
    FileSystem innerFs = FileSystems.newFileSystem(
        outerFs.getPath("/BOOT-INF/lib/core-1.0-SNAPSHOT.jar"), cl) ) {

    Path p = innerFs.getPath("images");
    Files.walk(p).forEach(path -> System.out.println(path));
}

这适用于JDK12或更高版本.

This works with JDK12 or newer.

在嵌套JAR内的文件夹中查找文件名

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