如何从依赖的jar访问资源文件？

Question

I have an android application that has a dependent library I created, referenced in build.gradle via compile {artifact_name}. The library needs to access a resource file in its resources dir(src/main/resources). Here is what I want to accomplish, but can't:

URL url = helper.class.getClassLoader().getResource("myfile.json");
FileReader fr = new FileReader(url.getPath());

myfile.json is in src/main/java/resources of my library. this led to an app crash saying "jar:file:/data/app/com.my.app/base.apk!/myfile.json" not found when trying to create the FileReader.

However, it can be found if I run it in a client class in the library itself.

Answer 1

Updated (I have some more time to give full answer)

In your case ClassLoader of helper class have an access to your file (there are why you get "jar:file:/data/app/com.my.app/base.apk!/myfile.json" in your FileReader instance).

But FileReader don't understand full-qualified URL s (only URL s with scheme file: or without any scheme, but you have outer scheme jar: - file accessible from jar file).

To read data in this case you should1 use combination of InputStreamReader and Class.getResourceAsStream :

ClassLoader cl = helper.class.getClassLoader();
InputStream is = cl.getResourceAsStream("myfile.json");
Reader r = new InputStreamReader(is);

PS in common situations you don't need access ClassLoader directly - Class will access it by itself. Only rare cases should use access to ClassLoader and in this situations you should really understand Class es and ClassLoader s very clear. I found out some usefull information: Class es method (both getResource and getResourceAsStream ) checks file only in same package while ClassLoader s methods checks (additionally) at root path (as I remember some of them checks in both places and today I checked that Class don't check root of jar file).