从jar包中读取资源文件

Rather than trying to address the resource as a File just ask the ClassLoader to return an InputStream for the resource instead via getResourceAsStream:

InputStream in = getClass().getResourceAsStream("/file.txt"); 
BufferedReader reader = new BufferedReader(new InputStreamReader(in));

As long as the file.txt resource is available on the classpath then this approach will work the same way regardless of whether the file.txt resource is in a classes/ directory or inside a jar.

The URI is not hierarchical occurs because the URI for a resource within a jar file is going to look like something like this: file:/example.jar!/file.txt. You cannot read the entries within a jar (a zip file) like it was a plain old File.

This is explained well by the answers to:

• How do I read a resource file from a Java jar file?
• Java Jar file: use resource errors: URI is not hierarchical

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指定编码

InputStreams don't have encodings. They're just streams of bytes. Readers are for text with an encoding. You can create a Reader with a specific charset from an InputStream like this:

Reader reader = new InputStreamReader(inputStream, "UTF-8");

If you're using a charset that's guaranteed to be supported on all Java platforms like UTF-8, you can avoid having to deal with impossible UnsupportedEncodingExceptions by using a constant from Guava's Charsets class like Charsets.UTF_8.