How to work with file path when addressing project folders content?

Let's say I have a structure

-bin/com/abc/开发者_JAVA技巧A.class
-src/com/abc/A.java
-config/info.txt

How to address the file info.txt from A class? Should we use "user.dir" property or "config/info.txt" so that it would work ? I'll compile this into the jar and after that the jar will be used from the servlet, but I don't think that's important cause this file is written and read from internal jar's methods only.

Just put it in the runtime classpath and use ClassLoader#getResourceAsStream() to get an InputStream of it. Putting it in the JAR file among the classes, or adding its (JAR-relative) path to the Class-Path entry of the JAR's manifest.mf file is more than sufficient.

ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
InputStream input = classLoader.getResourceAsStream("config/info.txt");
// Do your thing to read it.

Or if you actually want to get it in flavor of a java.io.File, then make use of ClassLoader#getResource(), URL#toURI() and the File constructor taking an URI:

ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
URL url = classLoader.getResource("config/info.txt");
File file = new File(url.toURI());
// Do your thing with it.

Do not use relative paths in java.io stuff. It would be dependent on the current working directory which you have no control over at any way. It's simply receipt for portability trouble. Just make use of the classpath.

That said, are you aware of the java.util.Properties API? It namely look like you're trying to achieve the same thing which is more easy to be done with propertiesfiles.