How to copy file inside jar to outside the jar?

Question

I want to copy a file from a jar. The file that I am copying is going to be copied outside the working directory. I have done some tests and all methods I try end up with 0

Answer 1

Java 8 (actually FileSystem is there since 1.7) comes with some cool new classes/methods to deal with this. As somebody already mentioned that JAR is basically ZIP file, you could use

final URI jarFileUril = URI.create("jar:file:" + file.toURI().getPath());
final FileSystem fs = FileSystems.newFileSystem(jarFileUri, env);

(See Zip File)

Then you can use one of the convenient methods like:

fs.getPath("filename");

Then you can use Files class

try (final Stream sources = Files.walk(from)) {
     sources.forEach(src -> {
         final Path dest = to.resolve(from.relativize(src).toString());
         try {
            if (Files.isDirectory(from)) {
               if (Files.notExists(to)) {
                   log.trace("Creating directory {}", to);
                   Files.createDirectories(to);
               }
            } else {
                log.trace("Extracting file {} to {}", from, to);
                Files.copy(from, to, StandardCopyOption.REPLACE_EXISTING);
            }
       } catch (IOException e) {
           throw new RuntimeException("Failed to unzip file.", e);
       }
     });
}

Note: I tried that to unpack JAR files for testing