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

To copy a file from your jar, to the outside, you need to use the following approach:

1. Get a InputStream to a the file inside your jar file using getResourceAsStream()
2. We open our target file using a FileOutputStream
3. We copy bytes from the input to the output stream
4. We close our streams to prevent resource leaks

Example code that also contains a variable to not replace the existing values:

public File saveResource(String name) throws IOException {
    return saveResource(name, true);
}

public File saveResource(String name, boolean replace) throws IOException {
    return saveResource(new File("."), name, replace)
}

public File saveResource(File outputDirectory, String name) throws IOException {
    return saveResource(outputDirectory, name, true);
}

public File saveResource(File outputDirectory, String name, boolean replace)
       throws IOException {
    File out = new File(outputDirectory, name);
    if (!replace && out.exists()) 
        return out;
    // Step 1:
    InputStream resource = this.getClass().getResourceAsStream(name);
    if (resource == null)
       throw new FileNotFoundException(name + " (resource not found)");
    // Step 2 and automatic step 4
    try(InputStream in = resource;
        OutputStream writer = new BufferedOutputStream(
            new FileOutputStream(out))) {
         // Step 3
         byte[] buffer = new byte[1024 * 4];
         int length;
         while((length = in.read(buffer)) >= 0) {
             writer.write(buffer, 0, length);
         }
     }
     return out;
}